Do Smart People Live Longer?

Posted on October 10, 2026 by Mahesh

Understanding IQ

Do Smart People Live Longer? What IQ and Mortality Studies Show

Do smart people live longer? On average, modestly: 16 studies of 1,107,022 people found a 24% lower risk of death per standard deviation of early-life intelligence. In 65,765 Scots the link was strongest for respiratory disease, heart disease and stroke. Here are the numbers.

By Arjun Vardhan, News & Research WriterPublished October 10, 2026 · 7 min readReviewed by Aarav Vardhan, Editor-in-Chief

Bars showing how much lower the risk of death from each cause was per one standard deviation higher childhood intelligence in 65,765 Scots followed for 68 years: respiratory disease 28 percent, coronary heart disease 25 percent, stroke 24 percent, injury 19 percent, dementia 16 percent and cancers not related to smoking 4 percent.

Do smart people live longer? On average, yes, but modestly. A meta-analysis of 16 studies covering 1,107,022 people and 22,453 deaths found that each 1 standard deviation (about 15 points) of higher intelligence in childhood or youth went with a 24% lower risk of death over 17 to 69 years of follow-up. The link is strongest for respiratory disease, heart disease and stroke, and weak for cancers unrelated to smoking. It is a population average built on early-life scores, and education, adult social class and smoking explain part of it. This guide sets out the three landmark studies, the numbers by cause of death, what a risk ratio does and does not tell one person, and what the explanations are. It is general information, not medical advice.

All causes: 24% lower risk of death per 1 SD higher score (95% CI 23% to 25%), pooled from 16 cohorts.
A whole country: in 65,765 Scots tested at age 11 and followed for 68 years, the hazard ratio per SD was 0.72 for respiratory disease, 0.75 for coronary heart disease and 0.76 for stroke.
Weakest links: cancers not related to smoking (0.96) and suicide (0.87, interval including 1.00).
What explains it: adjusting for education cut the link by 54% and for adult social class by 34% in the meta-analysis; childhood social class made almost no difference.
The catch: the scores were measured in childhood or youth, not as adults, and the studies report relative risks, not years of life.

Our news desk has covered the Scottish survey cohorts as a measurement story (childhood IQ scores and later-life health). This guide adds the numbers behind the headline. For related questions, see can an IQ test detect dementia, PTSD and IQ (another condition studied in the same kind of cohorts), and does IQ predict school success.

What the big studies measured

These studies share a design that matters for the answer: a cognitive test taken early in life, then records of who died and when. Testing early avoids a trap. Serious illness lowers test performance in later life, so an adult score could reflect a person who was already ill rather than one who was brighter (our reading). Population surveys such as the Scottish Mental Surveys of 1932 and 1947, which tested almost every 11-year-old in Scotland on a single day, provide the scores, and decades later they were linked to death records.

Whalley and Deary (2001) studied all 2,792 children in Aberdeen born in 1921 who sat the 1932 survey. They traced 79.9% (2,230) and checked survival to 1 January 1997. A 15-point disadvantage in mental ability at age 11 conferred a relative risk of 0.79 of being alive 65 years later (95% CI 0.75 to 0.84), and a 30-point disadvantage a relative risk of 0.63 (0.56 to 0.71). Men who died on active service in the Second World War had a relatively high IQ, an exception that suggests the pattern concerns ordinary causes of death (our reading). Overcrowding in the school catchment area was weakly related to death, and controlling for it did not alter the result.

Calvin and colleagues (2011) pooled 16 unrelated studies: 22,453 deaths among 1,107,022 participants. A 1 SD advantage in cognitive test scores went with a 24% (23% to 25%) lower risk of death over follow-up of 17 to 69 years. They found little sign of publication bias, and the association was similar for men and women.

Calvin and colleagues (2017) followed 33,536 men and 32,229 women born in Scotland in 1936 who took the 1947 survey, linking them to cause-of-death records through December 2015. This is the study that lets us split “risk of death” into causes.

Three landmark studies of early-life intelligence and mortality
Study	Who	Result
Whalley and Deary, 2001	2,230 traced from 2,792 Aberdeen children tested in 1932	Relative risk of survival to 76: 0.79 per 15-point disadvantage
Calvin et al., 2011	16 studies, 1,107,022 people, 22,453 deaths	24% lower risk of death per 1 SD advantage
Calvin et al., 2017	65,765 Scots tested in 1947, followed 68 years	Inverse link with every major cause of death, strongest for respiratory disease

Which causes of death? The numbers per standard deviation

Childhood intelligence was inversely associated with all major causes of death in the 2017 study. The table gives the age- and sex-adjusted hazard ratio per 1 SD (about 15 points) advantage; a ratio of 0.72 means 28% lower risk at a given age.

Hazard ratio per 1 SD higher childhood intelligence, by cause of death (Calvin et al., 2017)
Cause of death	Hazard ratio	95% interval
Respiratory disease	0.72	0.70 to 0.74
Coronary heart disease	0.75	0.73 to 0.77
Stroke	0.76	0.73 to 0.79
Injury	0.81	0.75 to 0.86
Smoking-related cancers	0.82	0.80 to 0.84
Digestive disease	0.82	0.79 to 0.86
Dementia	0.84	0.78 to 0.90
Suicide	0.87	0.74 to 1.02
Cancers not related to smoking	0.96	0.93 to 1.00

Two patterns stand out. The links were strongest for causes tied to smoking, lungs and the heart, and weak for suicide and for cancers not related to smoking, where the intervals include 1.00 (no difference). Among individual cancers the ratios ranged from 0.75 for lung cancer to 0.91 for hematopoietic cancers. The authors also report that the associations with coronary heart disease, smoking-related cancers, respiratory disease and dementia were somewhat stronger in women than in men.

What a hazard ratio means for one person

A hazard ratio of 0.76 per standard deviation does not mean a person lives 24% longer. It compares the chance of dying between groups: on average, a group 15 points higher has a 24% lower risk of death over the follow-up period (the 2011 pooled figure). If the ratio is the same at each step (an assumption), a 30-point advantage would give about 0.58 (0.76 x 0.76, our arithmetic). The Aberdeen study reports a different measure, the relative chance of being alive at 76 (0.63 for a 30-point disadvantage), so the two are not interchangeable. Converting these ratios into years of life needs life tables and an assumed baseline, and the studies above do not report it, so we do not put a number on it.

Individual scatter is large: these are averages across tens of thousands of people, and a ratio of 0.76 still leaves heavy overlap between groups (our reading). Use the IQ percentile calculator or the IQ bell curve to see how far 1 SD is, and note that scales differ: see standard deviation 15 versus 16.

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Why would intelligence relate to how long people live?

The studies show an association, and the more interesting question is why. The numbers that can be checked:

Education. In six studies that adjusted for it, education attenuated the hazard ratios by 54%.
Adult social class. In five studies, adjusting for adult socio-economic position attenuated them by 34%.
Childhood social class. In nine studies with the data, adjustment had almost no effect, so it does not look like a simple confounder.
Smoking and adult class in the 2017 replication sample. Together they partially attenuated the link, by 16% to 58%.
Other childhood confounders. In a representative subsample, adjusting for confounders including three childhood socio-economic indicators reduced the effect by only 10% to 26%.

Calvin and colleagues caution that attenuation can mean mediation (education is a step on the path), over-adjustment or confounding, and the data cannot tell these apart. Our news report sets out four candidate explanations: education and income, health behavior and health literacy (smoking is the clearest mediator), “system integrity” (the score as a marker of bodily robustness) and shared genetics, and concludes that none is sufficient alone. Related lifestyle questions appear in sleep and IQ, exercise and IQ, nutrition and IQ and IQ and alcohol; and for the education pathway, does school raise IQ.

What these studies cannot tell you

They are not about a score you take as an adult. The scores came from childhood or youth group tests, so an adult online result is not a forecast of lifespan (our reading).
They describe particular generations. The Scottish cohorts were born in 1921 and 1936, when smoking was more widespread than it is now; because smoking is a major pathway, the strength of the link today may differ (our reading).
They show association, not cause. Raising a score would not necessarily change longevity; education and health behavior are the stronger candidates for levers (our reading).
They report averages. Nothing here predicts a given person’s lifespan, and a lower score is not a medical risk factor on its own.

Quick answers

Do smart people live longer? On average, modestly: 24% lower risk of death per 1 SD higher early-life intelligence in 16 studies.
Which causes of death does it affect most? Respiratory disease (hazard ratio 0.72), coronary heart disease (0.75) and stroke (0.76).
Is it because smart people are richer? Partly: adjusting for adult social class and education shrinks the link by about a third to a half, and some remains.
Does a higher adult IQ add years? These studies did not test that; they used childhood scores.
Does a higher IQ protect against dementia? The hazard ratio for dementia death was 0.84 per SD, a modest link.

Sources

Whalley, L.J. and Deary, I.J. (2001): Longitudinal cohort study of childhood IQ and survival up to age 76, BMJ, 322(7290), 819.
Calvin, C.M. et al. (2011): Intelligence in youth and all-cause-mortality: systematic review with meta-analysis, International Journal of Epidemiology, 40(3), 626-644.
Calvin, C.M. et al. (2017): Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study, BMJ, 357, j2708.

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Bars showing odds ratios per one standard deviation lower cognitive ability in 3,258 US veterans: alcohol abuse or dependence 1.20, depression 1.32, PTSD 1.39, generalized anxiety disorder 1.43 and PTSD plus generalized anxiety disorder 2.50.

Understanding IQ

PTSD and IQ

PTSD and IQ: does PTSD lower intelligence? The best evidence says lower ability before a trauma raises the risk, with the top quarter at 48% lower risk in a 2,386-twin study. After PTSD, gaps appear in verbal learning and speed. Here is what the studies show.

October 10, 202610 min read

Research & Evidence

Does IQ Predict School Success?

IQ predicts school achievement better than any other single measure psychologists have found, and still leaves roughly three-quarters of the variation unexplained. Both halves of that sentence get ignored by somebody. Here are the actual correlations, what they mean for one child, and what accounts for the rest.

August 31, 20266 min read

Research & Evidence

Socioeconomic Status and IQ

Family circumstances track IQ scores, and the relationship is stranger than a simple gap. In the poorest families studied, genes explained almost none of the variation in childhood scores and shared environment explained most of it. In affluent families the pattern reversed. Here is what that finding does and does not support.

September 7, 20266 min read

Williams Syndrome and IQ

Posted on October 10, 2026 by Mahesh

Understanding IQ

Williams Syndrome and IQ: Average Scores, Range and the Uneven Profile

Williams syndrome and IQ: mean full-scale IQ was 61 in 62 adults, and 292 children averaged in the borderline range on the KBIT-2, stable from age 4 to 17. Language is a relative strength and visuospatial construction an extreme weakness. Here is what the studies show.

By Leon Falkner, Data & Research AnalystPublished October 10, 2026 · 9 min readReviewed by Aarav Vardhan, Editor-in-Chief

Bars showing anxiety in 45 children with Williams syndrome followed over time: 60 percent had an anxiety diagnosis at the first assessment, 82.2 percent at some point in the study and 51.1 percent had chronic, persistent anxiety.

Williams syndrome and IQ: the syndrome typically comes with a mild to moderate intellectual disability, but the numbers depend on the test and the age. In a study of 62 adults the mean full-scale IQ was 61. In 292 children tested on the Kaufman Brief Intelligence Test-2, the mean composite and both subscores fell in the borderline range, and on average scores stayed stable from age 4 to 17. The profile is uneven: language and auditory memory are relative strengths, while visuospatial construction is an extreme weakness. This guide explains how common Williams syndrome is, what the IQ studies report, why one total score hides the pattern, and what the research says about anxiety and reading. It is general information, not medical advice.

Rare: about 1 in 7,500 people, caused by the loss of one copy of 25 to 27 genes on chromosome 7.
Adults: mean full-scale IQ of 61 in 62 adults (average age 26).
Children: mean KBIT-2 composite in the borderline range in 292 children aged 4 to 17, with variability similar to the general population.
Stable: on average, standard scores did not change from age 4 to 17 in a longitudinal study.
Uneven: relative strengths in language and auditory rote memory; extreme weakness in visuospatial construction.
Anxiety: 82.2% of 45 children had an anxiety diagnosis at some point.

Williams syndrome is one of several genetic conditions where IQ research is common. Compare Down syndrome and IQ and fragile X and IQ, and for the wider question of when a score reflects intellectual disability, see low IQ versus learning disability.

What is Williams syndrome, and how common is it?

Williams syndrome is a microdeletion disorder: in most people with it, one copy of 25 to 27 genes on chromosome 7q11.23 is missing. A 2021 review in Nature Reviews Disease Primers lists cardiovascular disease (characteristically narrowing of the great arteries), a distinctive facial appearance and a specific cognitive and behavioral profile with intellectual disability and hypersociability as the cardinal features. The elastin gene (ELN) is behind the vascular and connective tissue features, while the transcription factor genes GTF2I and GTF2IRD1 are known to affect intellectual ability, social functioning and anxiety.

Prevalence rests on a small study. Strømme and colleagues (2002) studied 30,037 Norwegian children born between 1980 and 1985 in one county, in a survey of intellectual disability, and found three with Williams syndrome. Adding one case from a national survey who met their criteria gave an estimate of 1 in 7,500; all had the typical 7q11.23 deletion. They also reported that Williams syndrome accounted for about 6% of patients with a genetic cause of mental retardation (their term). With only a handful of cases behind it, treat 1 in 7,500 as an approximation, which is how the 2021 review writes it (“as many as” 1 in 7,500).

What is the average IQ in Williams syndrome?

Two studies give a feel for the numbers, and they are not directly comparable. Howlin, Davies and Udwin (1998) assessed a representative sample of 62 adults with Williams syndrome, average age 26, and reported a mean full-scale IQ of 61. Differences between verbal and performance IQ were smaller than in children, yet the subtest profile was almost identical. Reading, spelling, arithmetic and social adaptation were at a low level, generally around a 6 to 8 year age equivalent.

Pitts and Mervis (2016) described 292 children aged 4 to 17 on the Kaufman Brief Intelligence Test-2, a brief test (see KBIT-2). The mean IQ Composite, Verbal and Nonverbal standard scores were all in the borderline range relative to the general population, with variability similar to the general population. Scores did not track age (correlations close to 0), and there were no significant sex differences. Different tests, ages, eras and samples mean the two sets of means should not be lined up as a trend (our reading). Mervis and Klein-Tasman’s review (2000) puts the overall picture as mild to moderate intellectual disability or learning disability; in UK usage “learning disability” means intellectual disability.

What two studies report about IQ in Williams syndrome
Study	Who	Result
Howlin, Davies and Udwin, 1998	62 adults, average age 26	Mean full-scale IQ 61; reading, spelling and arithmetic around a 6 to 8 year age equivalent
Pitts and Mervis, 2016	292 children aged 4 to 17, KBIT-2	Mean composite, verbal and nonverbal scores in the borderline range; variability like the general population
Mervis et al., 2012	40 children tested 4 to 7 times over a mean of 5.06 years	On average stable from age 4 to 17, with large individual differences

Two practical limits apply. The KBIT-2 captures the full range of performance of 8- to 17-year-olds with Williams syndrome, but the authors say it lacks easy enough items for the lowest-scoring quarter of 4-year-olds, so floor effects are possible at the youngest ages. And the group is varied: “borderline” describes the mean, not each person. To see where a given number sits, use the IQ percentile calculator or the IQ bell curve page.

Does IQ change with age in Williams syndrome?

On average, little. Mervis, Kistler, John and Morris (2012) followed 40 children with genetically confirmed Williams syndrome who took the KBIT-2 four to seven times over a mean of about five years (mean age at first assessment 7.44). Composite IQ, Verbal and Nonverbal standard scores were stable on average from 4 to 17, although there were significant individual differences in starting level and, for Composite IQ and Nonverbal scores, in slope. In the larger cross-sectional sample, standard scores also showed close to zero correlation with age. A standard score compares a child with same-age peers, so a stable score means the child is gaining skills at roughly the same pace as peers (our reading). Maternal education was related to the Verbal standard score in both studies; that is an association, and could reflect genes, home environment or both (our reading).

The uneven profile: why one IQ number hides the pattern

Mervis and Klein-Tasman (2000) summarize the typical cognitive profile this way: relative to overall level, a clear strength in auditory rote memory, a strength in language, and an extreme weakness in visuospatial construction (building patterns or copying shapes). The personality profile involves high sociability, overfriendliness and empathy with an undercurrent of anxiety about social situations. Everyday skills show strength in socialization and communication and weakness in daily living and motor skills.

A single full-scale score averages a relative strength with an extreme weakness, so it describes neither well. That is why clinicians report subscores, and why our guides on verbal versus non-verbal IQ scores and reading an IQ test report matter here. You can see the contrast in the verbal and spatial formats. For other uneven profiles see savant syndrome and IQ tests.

A caution about the strengths. Martens, Wilson and Reutens (2008) reviewed 178 published studies and flagged small samples, the use and type of control groups, and multiple measures per task as methodological problems. They closely examined previously described “peaks” in the cognitive profile to test whether they hold up, so treat popular claims of special talents with care.

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Anxiety and IQ in Williams syndrome

Anxiety is one of the best-documented co-occurring issues. Woodruff-Borden and colleagues (2010) followed 45 children, aged 4 to 13 at the start, with repeated parent interviews: 60% had at least one anxiety diagnosis at the first assessment, 82.2% received one at some time, and 51.1% of the whole sample had chronic, persistent anxiety. Specific phobias and generalized anxiety disorder were the most common. IQ was not significantly related to having an anxiety disorder, but executive functioning was. In a larger sample of 194 children aged 6 to 17, Pitts and colleagues (2016) found that as IQ increased the probability of a specific phobia decreased, and that behavior regulation difficulties were the strongest predictor; the authors give a range of 37% to 56% for specific phobia across diagnostic interview studies. The studies measure different outcomes (any anxiety disorder versus specific phobia), which may explain the difference. For the general-population picture, see anxiety and IQ.

Learning to read with Williams syndrome

Richter, Cardoso-Martins and Mervis (2023) followed 69 children with Williams syndrome from age 6 to 7 to about age 9 to 10. Word reading at the second time point ranged from none to slightly above the level expected for age. Early phonological awareness and visual-spatial perception each explained unique variance, and children who had received systematic phonics instruction did significantly better than those taught other ways. The instruction type was classified rather than assigned, so this is an association, but it supports teaching sounds directly. It also fits the profile above, where language strengths can be put to work and visuospatial demands need extra support.

How to use an IQ score for someone with Williams syndrome

Ask for the profile. Verbal and nonverbal standard scores, plus working memory and processing speed where available, are more useful than the total.
Use the right test for the age. Brief tests may not separate low scores in young children; see WPPSI-IV and IQ testing for children.
Pair IQ with adaptive skills. Daily living and motor skills can lag behind verbal ability.
Remember the limits. An online test such as the IQ Metrics test is not a clinical assessment and is not designed for diagnosis.

Quick answers

What is the IQ of someone with Williams syndrome? A mean of 61 in one adult study; the mean was in the borderline range for children on the KBIT-2. Individuals vary widely.
Is Williams syndrome an intellectual disability? It typically comes with mild to moderate intellectual disability or learning disability, but the range is wide.
Do people with Williams syndrome have high verbal ability? Language is a relative strength compared with their own overall level, not compared with the general population.
Does IQ get lower with age? On average, standard scores were stable from age 4 to 17.
How common is it? About 1 in 7,500.

Sources

Kozel, B.A. et al. (2021): Williams syndrome, Nature Reviews Disease Primers, 7, 42.
Strømme, P., Bjørnstad, P.G. and Ramstad, K. (2002): Prevalence estimation of Williams syndrome, Journal of Child Neurology, 17(4), 269-271.
Howlin, P., Davies, M. and Udwin, O. (1998): Cognitive functioning in adults with Williams syndrome, Journal of Child Psychology and Psychiatry, 39(2), 183-189.
Pitts, C.H. and Mervis, C.B. (2016): Performance on the Kaufman Brief Intelligence Test-2 by children with Williams syndrome, American Journal on Intellectual and Developmental Disabilities, 121(1), 33-47.
Mervis, C.B., Kistler, D.J., John, A.E. and Morris, C.A. (2012): Longitudinal assessment of intellectual abilities of children with Williams syndrome: multilevel modeling of performance on the Kaufman Brief Intelligence Test-Second Edition, American Journal on Intellectual and Developmental Disabilities, 117(2), 134-155.
Mervis, C.B. and Klein-Tasman, B.P. (2000): Williams syndrome: cognition, personality, and adaptive behavior, Mental Retardation and Developmental Disabilities Research Reviews, 6(2), 148-158.
Martens, M.A., Wilson, S.J. and Reutens, D.C. (2008): Research review: Williams syndrome: a critical review of the cognitive, behavioral, and neuroanatomical phenotype, Journal of Child Psychology and Psychiatry, 49(6), 576-608.
Woodruff-Borden, J. et al. (2010): Longitudinal course of anxiety in children and adolescents with Williams syndrome, American Journal of Medical Genetics Part C, 154C(2), 277-290.
Pitts, C.H., Klein-Tasman, B.P., Osborne, J.W. and Mervis, C.B. (2016): Predictors of specific phobia in children with Williams syndrome, Journal of Intellectual Disability Research, 60(10), 1031-1042.
Richter, C.G., Cardoso-Martins, C. and Mervis, C.B. (2023): Longitudinal predictors of word reading for children with Williams syndrome, Reading and Writing, 36(8), 2119-2145.

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Bars showing the correlation between FMRP protein level and full-scale deviation IQ in fragile X syndrome: 0.73 across all 143 people, 0.45 in 44 females, 0.22 in 99 males and below 0.06 in 66 fully methylated full-mutation males.

Understanding IQ

Fragile X and IQ

Fragile X and IQ: fully methylated full-mutation males are described as moderate to severe intellectual disability, while females vary widely. A 2024 study of 143 people found a near-normal IQ curve shifted down, and FMRP protein level mattered except in fully methylated males.

October 10, 20269 min read

Understanding IQ

Down Syndrome and IQ

Most people with Down syndrome score in the mild to moderate range of intellectual disability, with an average IQ of around 50 and a typical range of about 30 to 70. The number hides a wide spread, a consistent profile of strengths, and test limits that matter more here than almost anywhere else.

September 16, 20267 min read

Scores & Scales

KBIT-2 Test

The KBIT-2 is a 20-minute IQ screen for ages 4 to 90 with three subtests: Verbal Knowledge, Riddles and Matrices. See how its scores work, what the 2022 KBIT-2 Revised changed, how closely it matches the WISC-V and KABC-II, and why it is a screen rather than a full evaluation.

October 5, 20268 min read

Fragile X and IQ

Posted on October 10, 2026 by Mahesh

Understanding IQ

Fragile X and IQ: What IQ Scores Look Like in Males and Females

By Alden Cross, Intelligence Research WriterPublished October 10, 2026 · 9 min readReviewed by Aarav Vardhan, Editor-in-Chief

Fragile X and IQ: males with a fully methylated full mutation are described as having a moderate to severe intellectual disability, while females vary far more, and about half fall in the borderline to intellectual disability range in one review. In a 2024 study of 143 people with fragile X syndrome (99 males, 44 females), IQ scores formed a near-normal bell curve shifted downward, not a single low cluster. Sex, mosaicism and how much of the FMRP protein the body still makes all move a person along that curve. This guide covers how common fragile X is, what the studies report for males and females, why scores differ so much, whether IQ declines with age, and what the premutation does and does not do. It is general information, not medical advice.

Common: the full mutation occurs in about 1 in 7,143 males and 1 in 11,111 females, from a pooled estimate with wide uncertainty.
Males: described as moderate to severe intellectual disability in the fully methylated full-mutation group, with scores spread out in a near-normal curve.
Females: milder and more variable; in one review about half were borderline or in the intellectual disability range and the rest average.
Mosaics: people with a mix of cell types had better intellectual functioning than matched people with the full mutation only.
Premutation carriers: no global change in general intelligence, memory or executive function in adults under 50.

Fragile X sits next to several conditions we have covered. Down syndrome is the other well-known genetic syndrome in this area (Down syndrome and IQ), and a companion guide covers the chromosome 7 condition (Williams syndrome and IQ). Fragile X also overlaps with autism, epilepsy and anxiety.

What is fragile X syndrome, and how common is it?

Fragile X syndrome is caused by a change in the FMR1 gene on the X chromosome. A stretch of DNA made of repeating CGG units grows; when it passes 200 repeats (the “full mutation”), the gene is silenced and the body stops making fragile X messenger ribonucleoprotein, or FMRP. A review in Nature Reviews Disease Primers calls it the leading inherited form of intellectual disability and autism spectrum disorder, with hyperactivity, impulsivity, anxiety, poor language development and seizures among the features. Repeat counts of roughly 55 to 199 are called a premutation.

Hunter and colleagues (2014) pooled 68 observations in a systematic review and meta-analysis. They estimated the full mutation at 1.4 per 10,000 males (95% CI 0.1 to 3.1) and 0.9 per 10,000 females (0.0 to 2.9), which they express as 1 in 7,143 and 1 in 11,111. The premutation was far more common: 11.7 per 10,000 males (1 in 855) and 34.4 per 10,000 females (1 in 291). The authors note that the full-mutation estimates are lower than in earlier reviews, and the wide intervals show how uncertain they remain. Because the gene is on the X chromosome, a male has one copy and a female has two, which is one reason the sexes differ (see is intelligence inherited from the mother or father for the wider picture of X-linked genes and IQ).

What IQ do males with fragile X have?

The most recent large look at IQ in fragile X is Schmitt and colleagues (2024), who tested 143 people aged 8 to 50 (99 males and 44 females). The paper describes fully methylated full-mutation males, the classic form, as marked by moderate to severe intellectual disability. What it adds is a picture of the spread. Using an abbreviated deviation IQ, the distribution of scores in the full male sample, and separately in the 66 fully methylated full-mutation males, was near-normal on skewness, kurtosis and a Shapiro-Wilk test: shifted below the general-population average, but shaped like an ordinary bell curve. The authors propose that fragile X has its own “standard curve” with its own mean and spread, and illustrate it with a male whose IQ of 45 would sit 1 standard deviation above the fragile X mean on that curve.

Two cautions come with such low scores. First, many standard tests have a floor, and the authors point to floor effects on standardized IQ measures as a limit on earlier research. The deviation-based score they used can fall below that floor: among fully methylated full-mutation males in the original samples, values ranged from -20 to 47 (our reading: these numbers describe relative standing, not a literal IQ on a standard test). Second, a single number says little about what a person can do day to day; see low IQ versus learning disability and what an IQ of 70 means for how scores and support needs relate.

What about females with fragile X?

Females have a second X chromosome, and in each cell one X is switched off at random, so some cells use the working copy of FMR1 and some the silenced one. That variation in FMR1 and FMRP expression is why the presentation in females is more variable and often milder, as Schmitt and colleagues explain. Keysor and Mazzocco’s developmental review (2002) found that approximately half of females with the syndrome had cognitive abilities in the borderline to intellectual disability range. The rest had average intellectual functioning but could still show relative deficits in math achievement, attention and executive function. Baker and colleagues (2019) compared 90 males and 36 females and found males had poorer intellectual functioning on all domains (p < 0.0001).

Why scores vary: mosaicism and the FMRP protein

Two molecular details explain a good part of the spread. Mosaicism means a person has a mix of cells, some with a full mutation and some with a smaller premutation-sized repeat (or different methylation). In Baker’s international cohort of 126 people aged 1 to 43, those with this mix had better intellectual functioning and fewer maladaptive behaviors than age- and sex-matched people with the full mutation only. Autism features were similar between the groups once intellectual functioning was taken into account.

FMRP level matters too. In the Schmitt sample, higher FMRP went with higher full-scale deviation IQ across everyone (r = .73), in females (r = .45) and in males (r = .22). But among the 66 fully methylated full-mutation males there was no relationship (all r below .06). Earlier work by the same group found that 40% to 50% of such males still express trace levels of FMRP, and they suggest that at very low levels other genetic, epigenetic and environmental factors may matter more, while saying that has not been directly tested. The pooled r = .73 is much larger than either sex alone, which is what you would expect if males and females differ on both FMRP and IQ (our reading), so do not read it as the strength of the link inside any one group.

What five studies report about IQ and the FMR1 gene
Study	Sample	Main finding
Schmitt et al., 2024	143 people aged 8 to 50 (99 males, 44 females)	IQ near-normally distributed but shifted down; FMRP linked to IQ except in fully methylated males
Baker et al., 2019	126 people aged 1 to 43 (90 males, 36 females)	Males lower than females; mosaics higher than full mutation only
Keysor and Mazzocco, 2002	Review of females with the full mutation	About half borderline to intellectual disability range
Wright-Talamante et al., 1996	35 males and 16 females (chart review)	IQ decline in 28% of males and 36% of females
Hunter et al., 2008	138 males and 506 females aged 18 to 50	No global neuropsychological effect of the premutation

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Does IQ decline with age in fragile X?

An often-quoted older study may be the source. Wright-Talamante and colleagues (1996) reviewed hospital records of 35 males with fragile X and 16 females with the full mutation, plus 9 male and 9 female controls, who had repeated IQ tests between 7 months and 13 years apart. A significant decline appeared in 10 of the 35 males (28%), 6 of the 16 females (36%), none of the 9 control males and 1 of the 9 control females. After taking starting IQ into account, the decline was greater in males with fragile X than in control males. The authors list limitations, including the use of the same IQ test over time, and the sample was small and retrospective.

Be careful with the word “decline”. An IQ is a comparison with same-age norms, so a person who keeps learning but more slowly than same-age peers can see the score fall without losing any skill (our reading; the abstract does not say which happened). We did not review later longitudinal work, so treat the question as open.

Premutation carriers: is IQ affected?

Hunter and colleagues (2008) tested 138 males and 506 females aged 18 to 50, from the general population and from families with a history of fragile X, on measures of general intelligence, memory and executive functioning. Among males, no association with repeat length was found for any factor. Among females, the only significant link was with self-reported attention problems, which were higher in premutation carriers. The authors concluded there is no global neuropsychological impact of carrying a premutation allele among adults under 50. The premutation is tied to other conditions, such as a tremor and ataxia syndrome mostly in older males and primary ovarian insufficiency in females, but those are not IQ effects.

How IQ is measured in fragile X, and what to keep in mind

Test choice matters. Young children are assessed with age-appropriate developmental or intelligence tests (see WPPSI-IV and the brief KBIT-2), and tests with high floors cannot separate low scores well.
Look at the profile, not only the total. Processing speed, working memory, cognitive flexibility and inhibitory control are described as especially affected.
Other conditions travel with it. Anxiety, hyperactivity (compare ADHD and IQ) and seizures can all affect how a child performs on test day.
Context for support decisions. For how scores are used in disability rules, see our report on low IQ and disability benefits; to place a number on a bell curve, use the IQ percentile calculator. An online test such as the IQ Metrics test is not a clinical assessment.

Quick answers

What is the IQ of someone with fragile X? There is no single IQ. Fully methylated full-mutation males are described as moderate to severe intellectual disability, with a spread of scores; females vary more.
Is fragile X an intellectual disability? It is the leading inherited cause of intellectual disability, but not every person with the gene change has one, especially among females and mosaics.
Do girls with fragile X have lower IQ? On average they score higher than males, and about half were borderline or in the intellectual disability range in one review.
Does the fragile X premutation lower IQ? Not globally, in adults under 50.
Does IQ get worse with age? An older chart review reported declines in about 3 in 10, with important limits; it may reflect slower gains than peers.

Sources

Hunter, J. et al. (2014): Epidemiology of fragile X syndrome: a systematic review and meta-analysis, American Journal of Medical Genetics Part A, 164A(7), 1648-1658.
Hagerman, R.J. et al. (2017): Fragile X syndrome, Nature Reviews Disease Primers, 3, 17065.
Schmitt, L.M., Nelson, M., Shaffer, R.C. and Erickson, C.A. (2024): A near normal distribution of IQ in fragile X syndrome, Scientific Reports, 14, 23058.
Baker, E.K. et al. (2019): Intellectual functioning and behavioural features associated with mosaicism in fragile X syndrome, Journal of Neurodevelopmental Disorders, 11, 41.
Keysor, C.S. and Mazzocco, M.M. (2002): A developmental approach to understanding fragile X syndrome in females, Microscopy Research and Technique, 57(3), 179-186.
Wright-Talamante, C. et al. (1996): A controlled study of longitudinal IQ changes in females and males with fragile X syndrome, American Journal of Medical Genetics, 64(2), 350-355.
Hunter, J.E. et al. (2008): No evidence for a difference in neuropsychological profile among carriers and noncarriers of the FMR1 premutation in adults under the age of 50, American Journal of Human Genetics, 83(6), 692-702.

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PTSD and IQ

Posted on October 10, 2026 by Mahesh

Understanding IQ

PTSD and IQ: Does PTSD Lower Intelligence, or Does Lower IQ Raise the Risk?

By Arjun Vardhan, News & Research WriterPublished October 10, 2026 · 10 min readReviewed by Aarav Vardhan, Editor-in-Chief

PTSD and IQ are linked, but the best evidence points mostly one way: a lower IQ before a trauma goes with a higher risk of developing PTSD, rather than PTSD mainly lowering IQ. Among 2,386 Vietnam-era twin veterans tested at about age 20, the top quarter on cognitive ability had a 48% lower risk of PTSD than the bottom quarter. After PTSD develops, studies do find weaker verbal learning, processing speed and attention (group gaps of about 0.5 to 0.6 standard deviations), but those are averages from 60 studies, not a number of IQ points lost. This guide sets out what the studies that tested people before and after trauma found, what the twin studies add, what childhood trauma changes, and how to read an IQ score when PTSD is part of the picture. It is general information, not medical advice.

Before the trauma: in 3,258 US veterans, each 1 standard deviation lower cognitive ability at enlistment went with an odds ratio of 1.39 for PTSD about 18 years later (unadjusted).
Twins: pairs with no PTSD scored highest, pairs where both twins had PTSD scored lowest, and the link ran through shared genes.
After the trauma: a meta-analysis of 60 studies (4,108 people) found the largest gaps in verbal learning (d = -0.62), processing speed (-0.59), attention and working memory (-0.50) and verbal memory (-0.46).
Children: on the WISC-III, children with PTSD scored lower on verbal subtests, while trauma-exposed children without PTSD did not differ from unexposed children.
Childhood violence: in two birth cohorts (2,232 and 1,037 people), the lower scores of victimized children were largely explained by deficits that predated the victimization.

PTSD rarely appears alone in this research. The same enlistment data link lower scores to anxiety and depression, and after a head injury the question changes shape again (can a concussion lower your IQ). For the long-term effects of early stress on scores, see toxic stress and IQ, and for a condition where thinking changes begin before diagnosis, see schizophrenia and IQ.

What is the PTSD and IQ question really asking?

Post-traumatic stress disorder is a condition that can follow exposure to a traumatic event. People with PTSD, as a group, tend to score lower on thinking tests than people without it. That fact has three possible explanations, and they lead to very different conclusions:

Trauma or PTSD lowers scores. The illness (or the stress it brings) interferes with attention and memory, so scores fall after the event.
Lower scores raise the risk. People who start with weaker thinking skills are more likely to develop PTSD after the same event, so the difference was already there.
A third factor drives both. Shared genes or a difficult childhood could affect scores and PTSD risk independently.

Only a design that measures people before the event can tell these apart, and such data are rare. Military induction testing provides it: recruits sit an aptitude test at about age 18 to 20, years before anyone knows who will see combat. Much of the strongest PTSD and IQ evidence comes from that source, which also means it concerns mostly men, the United States and one war era (our reading of the samples below).

Does a lower IQ raise the risk of PTSD? The studies that tested people first

Macklin and colleagues (1998) obtained military aptitude test results for 59 Vietnam combat veterans with PTSD and 31 without, and then tested their intelligence again. People with lower precombat intelligence were more likely to develop PTSD symptoms, even after adjusting for how much combat they saw. The link between current intelligence and PTSD stopped being significant once precombat intelligence was accounted for. The authors concluded that lower pretrauma intelligence increases risk, rather than PTSD lowering performance on intelligence tests.

Gale and colleagues (2008) followed 3,258 male veterans in the Vietnam Experience Study. Cognitive ability was measured at enlistment (mean age 20.4) and psychiatric disorders by structured interview at mean age 38.3. For each 1 standard deviation (about 15 IQ points on most scales) lower, the unadjusted odds ratio for current PTSD was 1.39 (95% CI 1.18 to 1.67), against 1.43 for generalized anxiety disorder, 1.32 for depression and 1.20 for alcohol abuse or dependence. PTSD together with generalized anxiety disorder had an odds ratio of 2.50 (1.41 to 4.55). If the effect were the same at each step (an assumption), two standard deviations lower would multiply the odds by about 1.9 (1.39 x 1.39, our arithmetic). That is a real but modest shift, and an odds ratio is not a probability.

Parslow and Jorm (2007) took a different route. They tested a random sample of 2,097 young adults on word recall, digit span, coding speed and vocabulary in 1999–2000, then retested them in 2003–2004 after a major fire in their region. Among the 1,599 who were exposed, higher reexperiencing and arousal symptoms were more consistently linked to poorer pretrauma scores on all five measures than to later change.

Four studies that measured thinking skills before trauma exposure
Study	Who	Main finding
Macklin et al., 1998	59 PTSD and 31 non-PTSD combat veterans	Lower precombat intelligence predicted PTSD symptoms after adjusting for combat exposure
Kremen et al., 2007	2,386 male Vietnam-era twin veterans	Top ability quartile had 48% lower PTSD risk than the bottom quartile
Gale et al., 2008	3,258 male veterans, tested at mean age 20.4 and interviewed at 38.3	Odds ratio 1.39 for PTSD per 1 SD lower ability (unadjusted)
Parslow and Jorm, 2007	1,599 young adults exposed to a major fire	Poorer pretrauma scores on all five measures went with more PTSD symptoms

What the twin studies add

Twins let researchers separate genes from the event itself. Kremen and colleagues (2007) studied the 2,386 twin veterans using their Armed Forces Qualification Test percentile before induction. There was a dose-response pattern: the higher the pre-exposure ability, the lower the PTSD risk. Pairs in which neither twin had PTSD had the highest scores, pairs in which both had it had the lowest, and discordant pairs fell in between. In the authors’ analysis, genetic influences on pre-exposure cognitive ability explained 5% of the variation in PTSD, and all of that relationship was explained by common genes.

Gilbertson and colleagues (2006) went further with identical twin pairs in which only one brother was exposed to combat. When the exposed brother developed PTSD, his unexposed twin largely performed the same on the cognitive tests, and both did worse than non-PTSD veterans and their brothers. A twin who never saw combat cannot have been affected by combat, so the lower performance looks like a pre-existing characteristic rather than a result of the trauma (the authors’ interpretation: such functions may be premorbid risk or protective factors).

Does PTSD itself change thinking test results?

Probably a little, in specific domains, which is a different claim from lowering IQ. Scott and colleagues (2015) pooled 60 studies with 4,108 participants: 1,779 with PTSD, 1,446 trauma-exposed comparison participants and 895 healthy comparison participants with no trauma exposure. The effects ranged widely. The largest were in verbal learning (d = -0.62), speed of information processing (-0.59), attention and working memory (-0.50) and verbal memory (-0.46). Gaps were larger in treatment-seeking than community samples, and they were affected by IQ differences between the groups being compared. For scale: a gap of -0.6 standard deviations would be about 9 points if it were expressed on an IQ-style scale with a standard deviation of 15 (our arithmetic), but these are single-skill tests, so that is a yardstick for size, not a measured loss of IQ.

The same pattern shows up in smaller studies. In Parslow and Jorm’s fire sample, higher reexperiencing and arousal symptoms went with less improvement in word recall at the second interview. The authors suggest that PTSD symptoms may cause a relative decline in some measures of verbal memory, but call the vulnerability finding the more robust one. Saigh and colleagues (2006) compared WISC-III scores in traumatized youth with PTSD, trauma-exposed youth without PTSD and nonexposed controls, none of whom had other major childhood psychiatric disorders. The PTSD group scored lower on verbal subtests but not on performance subtests, and the trauma-exposed group without PTSD did not differ from controls. Trauma exposure alone was not what went with lower verbal IQ; PTSD was. A single comparison like that cannot show which came first (our reading), which is why the before-and-after designs above carry more weight.

Speed, attention and working memory are among the skills a timed test samples, so a person with active symptoms may score lower on a given day than their usual level (our reading, not a finding of these studies). See our guides on processing speed and IQ and executive function versus IQ for how those skills relate to the score.

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Childhood trauma and IQ: a separate question

Danese and colleagues (2017) used two population cohorts: the E-Risk Study (2,232 children followed to age 18) and the Dunedin Study (1,037 people followed to age 38). Children exposed to violence had pervasive impairments in general intelligence, executive function, processing speed, memory, perceptual reasoning and verbal comprehension. However, those deficits were largely explained by cognitive deficits that predated the victimization and by confounding genetic and environmental risks; the design included comparisons of twins discordant for victimization. The authors call the association largely noncausal and suggest that cognitive deficits are individual risk factors for victimization as well as complicating features during treatment. “Largely” is not “entirely”, and the study does not say that severe, prolonged adversity never affects a child.

Our news desk covered the brain-scan side in a PNAS study on adversity and cognition, where the links were small and one did not replicate. Koenen and colleagues (2009) add that in Dunedin, lower childhood IQ predicted adult depression and anxiety, which fits the wider pattern of lower scores marking vulnerability to several conditions.

What these findings do not mean

They do not mean PTSD reflects low intelligence. The effect is a shift in average risk, and people across the whole range of scores develop PTSD.
They do not mean a score can predict PTSD in one person. An odds ratio of 1.39 per standard deviation is a population statistic, and an IQ score is not a screening tool for PTSD (our reading).
They do not apply to everyone. The core samples are male veterans or a regional fire sample; whether the pattern is the same for other traumas and groups is less certain (our reading).
They do not show what recovery does to scores. The studies described here do not tell us whether treatment or symptom relief changes test results.

Taking an IQ test when you have PTSD

Treat any single score as a snapshot. Every full-scale IQ score carries a margin of error (see IQ score margin of error), and attention, speed and memory are the areas where the research shows the biggest PTSD-related differences. If a score will be used for school, work or a legal or disability decision, a psychologist can assess it in context; our guide to reading an IQ test report explains what the pieces mean, and professional IQ tests covers what clinicians use. An online test such as the IQ Metrics test is not a clinical assessment. Use the IQ percentile calculator to see where a number sits on the bell curve. If trauma symptoms are affecting your life, a doctor or mental health professional can help.

Related health-and-IQ research from the same cohorts is covered in do smart people live longer.

Quick answers

Does PTSD lower IQ? The strongest evidence says pre-existing lower ability raises PTSD risk. After PTSD develops, group gaps appear in verbal learning, speed and attention, but they are not a measured loss of IQ.
Does a low IQ cause PTSD? It is a risk factor, not a cause: top-quartile ability had 48% lower risk than the bottom quartile in one twin study.
Are smart people less likely to get PTSD? On average, somewhat (odds ratio 1.39 per standard deviation lower), but people at every level develop it.
Does childhood trauma lower IQ? Victimized children score lower, but in two cohorts much of the gap predated the victimization.
Is there a typical IQ for people with PTSD? No; the studies report group differences, not a typical score.

Sources

Macklin, M.L. et al. (1998): Lower precombat intelligence is a risk factor for posttraumatic stress disorder, Journal of Consulting and Clinical Psychology, 66(2), 323-326.
Kremen, W.S. et al. (2007): Pretrauma cognitive ability and risk for posttraumatic stress disorder: a twin study, Archives of General Psychiatry, 64(3), 361-368.
Gale, C.R. et al. (2008): Cognitive ability in early adulthood and risk of 5 specific psychiatric disorders in middle age: the Vietnam Experience Study, Archives of General Psychiatry, 65(12), 1410-1418.
Gilbertson, M.W. et al. (2006): Neurocognitive function in monozygotic twins discordant for combat exposure: relationship to posttraumatic stress disorder, Journal of Abnormal Psychology, 115(3), 484-495.
Parslow, R.A. and Jorm, A.F. (2007): Pretrauma and posttrauma neurocognitive functioning and PTSD symptoms in a community sample of young adults, American Journal of Psychiatry, 164(3), 509-515.
Scott, J.C. et al. (2015): A quantitative meta-analysis of neurocognitive functioning in posttraumatic stress disorder, Psychological Bulletin, 141(1), 105-140.
Saigh, P.A. et al. (2006): The intellectual performance of traumatized children and adolescents with or without posttraumatic stress disorder, Journal of Abnormal Psychology, 115(2), 332-340.
Danese, A. et al. (2017): The origins of cognitive deficits in victimized children: implications for neuroscientists and clinicians, American Journal of Psychiatry, 174(4), 349-361.
Koenen, K.C. et al. (2009): Childhood IQ and adult mental disorders: a test of the cognitive reserve hypothesis, American Journal of Psychiatry, 166(1), 50-57.

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Bars showing how much the odds or hazard of an anxiety-type disorder rise for each 15 points lower IQ: generalized anxiety disorder 1.43 and post-traumatic stress disorder 1.39 among 3,258 US veterans, and 1.51 for hospital admission with a neurotic disorder among 1,049,663 Swedish men, measured against a no-difference line at 1.0.

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Epilepsy and IQ

Posted on October 9, 2026 by Mahesh

Understanding IQ

Epilepsy and IQ: Does Epilepsy Lower Intelligence? What the Studies Show

Does epilepsy lower IQ? Not in most children: in a 613-child cohort, 73.6% had normal cognition and about 1 in 4 did not. Early onset, a known cause and continuing treatment predicted lower scores, and valproate in pregnancy went with an age-6 IQ of 97. Here is what the studies show.

By Arjun Vardhan, News & Research WriterPublished October 9, 2026 · 7 min readReviewed by Aarav Vardhan, Editor-in-Chief

Bars showing global cognitive function in 613 children followed from the diagnosis of epilepsy: 73.6 percent within the normal range, 5.1 percent borderline, 10.8 percent with intellectual disability and 10.6 percent severely impaired or unclassified.

Epilepsy and IQ are less tightly tied than many assume: epilepsy does not by itself mean a low IQ. In a community-based study that followed 613 children from the time epilepsy was diagnosed, 73.6% had global cognitive function in the normal range, and about 1 in 4 had subnormal function. Onset before age 5, a known underlying cause, an epileptic encephalopathy and continuing medication were each strongly linked to lower scores. Seizure medicines matter too: children whose mothers took valproate in pregnancy had a mean IQ of 97 at age 6, against 105 to 108 after other drugs. This guide covers how common epilepsy is, what the childhood and adult studies show, what predicts lower scores, and how to read an IQ test when seizures or medicines are part of the picture. It is general information, not medical advice.

Common: 6.38 per 1,000 people have active epilepsy, pooled across 222 studies.
Children: 73.6% normal, 5.1% borderline, 10.8% intellectual disability and 10.6% severely impaired or unclassified in a community-based cohort.
Predictors: onset under 5 years, a symptomatic cause, epileptic encephalopathy and current treatment were each strongly associated with lower cognitive function.
The other direction: 22.2% of people with intellectual disability have epilepsy.
Medicines in pregnancy: age-6 IQ was 97 after valproate, 105 after carbamazepine and 108 after lamotrigine or phenytoin.
Adults: in chronic temporal lobe epilepsy, 20% to 25% showed adverse cognitive change over four years, mainly in memory.

Epilepsy is common alongside other conditions we have covered: about 1 in 4 children with cerebral palsy had it in a systematic review (cerebral palsy and IQ), and it is more frequent in people with Down syndrome. For a very different brain-based condition where the timing of onset also shapes the thinking changes, see schizophrenia and IQ. After a head injury, see can a concussion lower your IQ.

What is epilepsy, and how common is it?

Epilepsy is a condition in which the brain has a lasting tendency to produce unprovoked seizures. It is not one disease: the cause, the type of seizure and the age at which it starts all differ, which is why no single IQ describes people with it. Fiest and colleagues pooled 222 population-based studies and found a point prevalence of active epilepsy of 6.38 per 1,000 people (95% CI 5.57 to 7.30), a lifetime prevalence of 7.60 per 1,000 and an incidence rate of 61.44 per 100,000 person-years. Prevalence and incidence were higher in low- and middle-income countries, and prevalence did not differ by age group, sex or study quality. Epilepsies of unknown cause and those with generalized seizures had the highest prevalence.

Does epilepsy lower IQ? What a community-based study found

Berg and colleagues followed children from the moment epilepsy was diagnosed, in a community-based sample rather than a specialist clinic, which tends to see more severe cases. Over a median of 10.5 years they classified cognitive function from neurologists’ and school records, repeated parent interviews and, for over half the children, standardized neuropsychological testing.

Global cognitive function in 613 children with newly diagnosed epilepsy (Berg and colleagues, 2008)
Level	Children	Share
Within the normal range	451	73.6%
Borderline	31	5.1%
Mild intellectual disability	21	3.4%
More severe intellectual disability	45	7.3%
Neurologically devastated	29	4.7%
Impaired, not further classified	36	5.9%

The paper uses the older term mental retardation for the two disability categories, and the six groups add up to 613 children. The authors summarize the result as subnormal global cognitive function in approximately one of four children; for their statistical models, subnormal meant a full-scale IQ below 80. Note what the table also says: nearly three quarters had cognition in the normal range, and the abnormal group is itself varied.

What predicts lower scores in childhood epilepsy?

Five features were each strongly associated with level of cognitive function (all p < 0.0001): age at onset under 5 years, a symptomatic cause (a known underlying brain problem), epileptic encephalopathy (a syndrome in which the epileptic activity itself is thought to contribute to cognitive and behavioral problems), remission status and current anti-seizure medication. In the multivariable model all but remission status contributed independently.

Be careful with the last one. The authors point out that these factors are strongly intercorrelated. Children who are still taking medicine are, on average, children whose epilepsy has not settled, and the study cannot say that the medicine lowers their scores (our reading).

Intellectual disability and epilepsy: the other direction

The link also runs from the other side. A systematic review by Robertson and colleagues pooled 38 studies in general samples of people with intellectual disabilities and found epilepsy in 22.2% (95% CI 19.6% to 25.1%), with prevalence rising with the level of intellectual disability. For people with Down syndrome the pooled figure from 13 studies was 12.4%, and it increased with age. Both conditions can come from the same underlying brain problem, which is one reason the symptomatic-cause group above scored lower (our reading). A person with epilepsy and a person with an intellectual disability are different groups with an overlap.

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Seizure medicines and thinking

Eddy, Rickards and Cavanna’s 2011 review concluded that anti-seizure drugs can affect cognition, with effects that vary with the drug, the dose and the patient; some agents may even help, and the evidence is hard to compare because studies differ in design, groups and tests. The clearest evidence on IQ concerns exposure before birth.

In the NEAD study, Meador and colleagues followed pregnant women with epilepsy taking one drug (carbamazepine, lamotrigine, phenytoin or valproate) at 25 centres in the UK and USA; the primary analysis included 305 mothers and 311 children. Age-6 IQ, adjusted for maternal IQ, drug, dose, gestational age and folate use, was lower after valproate (mean 97, 95% CI 94 to 101) than after carbamazepine (105, 102 to 108), lamotrigine (108, 105 to 110) or phenytoin (108, 104 to 112). Higher valproate doses went with lower IQ (r = -0.56); the other drugs showed no such dose relationship.

Mean IQ at age 6 by drug taken in pregnancy (NEAD study)
Drug	Mean IQ (95% CI)
Valproate	97 (94 to 101)
Carbamazepine	105 (102 to 108)
Lamotrigine	108 (105 to 110)
Phenytoin	108 (104 to 112)

This is a risk to discuss with a doctor before and during pregnancy. It is not a reason to stop any medicine alone, because stopping can bring seizures back, and seizures carry their own risks. The study was observational, with assessors masked to drug exposure, and it describes groups of children, not any one child.

Adults: what happens to thinking in long-standing epilepsy?

Hermann and colleagues followed 46 adults with chronic temporal lobe epilepsy and 65 healthy controls for four years. The patients’ cognitive trajectory differed from the controls’: lack of practice effects, the small gain that comes from taking a test again, was common, and frank adverse change appeared in a subset of 20% to 25%, particularly in memory. Decline went with abnormalities on the baseline MRI, lower baseline intellectual capacity, longer duration of epilepsy and older age. So the headline for adults is the subset: most patients did not show frank decline over the four years.

An earlier study of 53 people with temporal lobe epilepsy and 62 controls found that onset in childhood, before age 14, but not in adulthood, went with smaller total brain tissue and lower intellectual and memory scores, and that longer duration went with worse scores in the childhood-onset group. The authors proposed that early-onset temporal lobe epilepsy reduces cerebral reserve and puts people at risk of progressive decline if it is chronic and unremitting. For the practice-effect idea, see practice effects on cognitive tests.

Taking an IQ test with epilepsy

A score reflects performance on the day. Fatigue and poor sleep can lower anyone’s result (see sleep loss and test performance). Tell the psychologist about your seizures and medicines.
The profile matters. Clinical assessment looks at memory, speed and attention as well as the total; memory was the domain that most often changed in the adult study.
Repeat tests carry practice effects and error. See the margin of error explained.
An online test is not a clinical tool. It should not guide decisions about schooling or support; a clinical assessment can. See professional IQ tests.

Quick answers

Does epilepsy lower IQ? Not in most children: 73.6% in a community-based cohort had normal global cognitive function. Early onset, a known cause, an epileptic encephalopathy and continuing treatment predicted lower scores.
What is the average IQ of someone with epilepsy? There is no single average. The studies describe ranges and subgroups, and the group is very varied.
Can seizure medicine lower IQ? Effects vary by drug and dose. The clearest finding concerns valproate taken in pregnancy (age-6 IQ 97 against 105 to 108). Do not stop medicine without medical advice.
Is epilepsy common in intellectual disability? Yes: 22.2% in a pooled review.
Does temporal lobe epilepsy cause memory decline? In a subset, 20% to 25% over four years in one study; most patients did not decline.

Sources

Fiest, K.M. et al. (2017): Prevalence and incidence of epilepsy: a systematic review and meta-analysis of international studies, Neurology, 88(3), 296-303.
Berg, A.T. et al. (2008): Global cognitive function in children with epilepsy: a community-based study, Epilepsia, 49(4), 608-614.
Robertson, J., Hatton, C., Emerson, E. and Baines, S. (2015): Prevalence of epilepsy among people with intellectual disabilities: a systematic review, Seizure, 29, 46-62.
Eddy, C.M., Rickards, H.E. and Cavanna, A.E. (2011): The cognitive impact of antiepileptic drugs, Therapeutic Advances in Neurological Disorders, 4(6), 385-407.
Meador, K.J. et al. (2013): Fetal antiepileptic drug exposure and cognitive outcomes at age 6 years (NEAD study): a prospective observational study, The Lancet Neurology, 12(3), 244-252.
Hermann, B.P. et al. (2006): Cognitive prognosis in chronic temporal lobe epilepsy, Annals of Neurology, 60(1), 80-87.
Hermann, B.P., Seidenberg, M. and Bell, B. (2002): The neurodevelopmental impact of childhood onset temporal lobe epilepsy on brain structure and function and the risk of progressive cognitive effects, Progress in Brain Research, 135, 429-438.

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Bars showing three estimates of intellectual disability in cerebral palsy: about 50 percent (1 in 2) in a 2012 systematic review of population-based studies, 45 percent of 1,141 people on an Australian register, and 38 percent of 21 children with hemiplegic cerebral palsy in Stockholm; the remainder in each group did not have an intellectual disability.

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