Resolving the Genetic and Environmental Sources of the Correlation Between Height and Intelligence: A Study of Nearly 2600 Norwegian Male Twin Pairs

Co-recovery of physical size and cognitive ability from infancy to adolescence: A twin study

This study tested phenotypic and biometric associations between physical and cognitive catch-up growth in a community sample of twins (n = 1285, 51.8% female, 89.3% White). Height and weight were measured at up to 17 time points between birth and 15 years, and cognitive ability was assessed at up to 16 time points between 3 months and 15 years. Weight and length at birth were positively associated with cognitive abilities in infancy and adolescence (r's = .16-.51). More rapid weight catch-up growth was associated with slower, steadier cognitive catch-up growth. Shared and nonshared environmental factors accounted for positive associations between physical size at birth and cognitive outcomes. Findings highlight the role of prenatal environmental experiences in physical and cognitive co-development.

Height and cognitive assessments in a cohort of US schoolchildren, kindergarten through fifth grade

An oft-repeated finding in child development research is that height and cognitive ability are positively related. Much of this work is limited in its ability to track height and cognitive development over time, with key constraints being the availability of longitudinal data and measures of ability that are comparable over time. This study evaluates the associations between height and assessments of reading, math, and science in a representative sample of US schoolchildren followed from kindergarten through fifth grade. Associations between height and assessment scores at each grade level, and height-growth and changes in scores over grade levels, are examined. The results suggest modest associations between concurrent height and assessment scores at each grade level that are robust to socioeconomic and school controls. There is limited association between height-growth and assessment outcomes, which is shown only for females. There is also little indication that height or height-growth is associated with improvements in scores. The findings suggest a modest association between height and cognitive ability in contemporary US schoolchildren, being attributed mostly to growth before kindergarten. The findings are consistent with the view that social and biological forces in early-life facilitate both physical and cognitive development.

Nonlinear Catch-Up Growth in Height, Weight, and Head Circumference from Birth to Adolescence: A Longitudinal Twin Study

Owing to high rates of prenatal complications, twins are, on average, substantially smaller than population norms on physical measurements including height, weight, and head circumference at birth. By early childhood, twins are physically average. This study is the first to explore the process of catch-up growth by fitting asymptotic growth models to age-standardized height, weight, and head circumference measurements in a community sample of twins (n = 1281, 52.3% female) followed at up to 17 time points from birth to 15 years. Catch-up growth was rapid over the first year and plateaued around the population mean by early childhood. Shared environmental factors accounted for the majority of individual differences in initial physical size (57.7-65.5%), whereas additive genetic factors accounted for the majority of individual differences in the upper asymptotes of height, weight, and head circumference (73.4-92.6%). Both additive genetic and shared environmental factors were associated with variance in how quickly twins caught up. Gestational age and family SES emerged as important environmental correlates of physical catch-up growth.

Nonlinear Catch-Up Growth in Height, Weight, and Head Circumference from Birth to Adolescence: A Longitudinal Twin Study

Owing to high rates of prenatal complications, twins are, on average, substantially smaller than population norms on physical measurements including height, weight, and head circumference at birth. By early childhood, twins are physically average. This study is the first to explore the process of catch-up growth by fitting asymptotic growth models to age-standardized height, weight, and head circumference measurements in a community sample of twins ( n  = 1,281, 52.3% female) followed at up to 17 time points from birth to 15 years. Catch-up growth was rapid over the first year and plateaued around the population mean by early childhood. Shared environmental factors accounted for the majority of individual differences in initial physical size (57.7%-65.5%), whereas additive genetic factors accounted for the majority of individual differences in the upper asymptotes of height, weight, and head circumference (73.4%-92.6%). Both additive genetic and shared environmental factors were associated with variance in how quickly twins caught up. Gestational age and family SES emerged as important environmental correlates of physical catch-up growth.

Nutrition within the household: 18th through early 20th century female and male statures

When other measures for material conditions are scarce or unreliable, the use of height is now common to evaluate economic conditions during economic development. However, throughout US economic development, height data by gender have been slow to emerge. Throughout the late 19th and early 20th centuries, female and male statures remained constant. Agricultural workers had taller statures than workers in other occupations, and the female agricultural height premium was over twice that of males. For both females and males, individuals with fairer complexions were taller than their darker complexioned counterparts. Gender collectively had the greatest explanatory effect associated with stature, followed by age and nativity. Socioeconomic status and birth period had the smallest collective effects with stature.

No Evidence for a Relationship between Intelligence and Ejaculate Quality

Genetic quality may be expressed through many traits simultaneously, and this would suggest a phenotype-wide fitness factor. In humans, intelligence has been positively associated with several potential indicators of genetic quality, including ejaculate quality. We conducted a conceptual replication of one such study by investigating the relationship between intelligence (assessed by the Raven Advanced Progressive Matrices Test-Short Form) and ejaculate quality (indexed by sperm count, sperm concentration, and sperm motility) in a sample of 41 men (ages ranging 18 to 33 years; M = 23.33; SD = 3.60). By self-report, participants had not had a vasectomy, and had never sought infertility treatment. We controlled for several covariates known to affect ejaculate quality (e.g., abstinence duration before providing an ejaculate) and found no statistically significant relationship between intelligence and ejaculate quality; our findings, therefore, do not match those of Arden, Gottfredson, Miller et al. or those of previous studies. We discuss limitations of this study and the general research area and highlight the need for future research in this area, especially the need for larger data sets to address questions around phenotypic quality and ejaculate quality.

The Norwegian Armed Forces Health Registry conscription board health examinations 1968-2018

Aim: The aim of the study is to encourage further research initiatives and collaborations based on Norwegian Armed Forces Health Registry (NAFHR) data by presenting basic information on the data contained therein. Methods: We describe how conscription board health examinations (CBHEs) are carried out, how results are recorded in the NAFHR, and the completeness of NAFHR data that are electronically available for research purposes. Results: In December 2018, the NAFHR contained data on nearly 1.5 million Norwegian citizens (95% men) who attended CBHE in 1968-2018 at the age of 17-19 years. The percentage of persons included from each birth cohort has varied as the Armed Forces' personnel requirements and filing procedures have changed, increasing from 73% of eligible men born in 1950 to 95% of eligible men born in 1960-1991. In 2010 a preselection of candidates was implemented wherefore less than half of men born in 1992-2000 are registered in the NAFHR. Information on aerobic fitness, cognitive general ability, height and weight is registered for approximately 95% of individuals included in the NAFHR. The NAFHR contains more detailed health information for CBHEs that took place as from 1980, and information included from 2011 onwards is the most detailed. Unique, national personal identification numbers may be used to link the NAFHR to other health registries or data sources for public health research. Conclusions: The NAFHR contains CBHE data on the majority of Norwegian men and a substantial number of women born since 1950. NAFHR data represent a valuable resource for research collaborations.

Influence of height on likelihood of employment, occupational sorting, and earnings in 27 post-communist countries

OBJECTIVES

We study the influence of height on labour market outcomes using micro-data from a recent survey that cover 27 post-communist countries. Specifically, we focus on the influence of height on three dimensions of labour market outcome: (1) likelihood of employment, (2) occupational sorting, and (3) earnings.

METHODS

We use micro-data from 2016 Life-In-Transition survey (LITS) which was jointly conducted by the European Bank for Reconstruction and Development and the World Bank. We run several types of regression to show how height influences (1) likelihood of employment, (2) occupational sorting, and (3) earnings.

RESULTS

When controlling for a comprehensive set of covariates, for each 10 cm increase in height, the probability of getting a job increases by 1% points for males and by 3 for females. Equally, for each 10 cm increase in height, the probability of getting a job increases by 2% points in urban areas and rural areas. Our findings demonstrate that taller women and men are more likely: (a) being an employer rather than an employee; (b) to be employed in higher-paid and more prestigious sectors of finance, insurance, and real estate; (c) to be employed in private enterprises. Finally, when occupational sorting and socio-demographics are controlled for, a 10 cm increase in height results in a 5% increase in earning for men, and a 12% increase in earnings for women.

CONCLUSIONS

Using a diverse sample of 27 post-communist countries, we found that taller individuals have better labour market outcomes in terms of employment, occupational sorting, and earnings.

The relationship between height and leadership: Evidence from across Europe

To better explicate the well-researched finding that taller individuals have higher wages on average, potential mechanisms should be studied in detail. The present analysis investigates the relationship between height and the probability of being in a leadership position in the workplace using multinational European Social Survey data from 19 countries. Studying full-time, employed individuals between 20 and 55 years of age reveals considerable country differences which is beneficial for the estimated multilevel models as variation is increased. The results indicate a statistically significant effect whereby women are 0.15 percentage points more likely to be in a leadership position for each additional centimetre of absolute height when controlling for education and occupational position whereas there is no effect for men. In order to study the relevance of absolute vs relative height, which is the difference to the local peer-group, regional data is utilized. The main findings are that there is no effect of relative height for men but a statistically significant effect for women. For them, absolute and relative effects are about equally strong.

Two by two, inch by inch: Height as an indicator of environmental conditions during childhood and its influence on earnings over the life cycle among twins

Adult height is a function of genetic predispositions and environmental influences during childhood. Hence, any variation in height among monozygotic twins, who share genetic predispositions, is bound to reflect differences in their environmental exposure. Therefore, a height premium in earnings among monozygotic twins also reflects such exposure. In this study, we analyze the height premium over the life cycle among Swedish twins, 10,000 of whom are monozygotic. The premium is relatively constant over the life cycle, amounting to 5-6% higher earnings per decimeter for men and less for women, suggesting that environmental conditions in childhood and youth affect earnings over most of the adult life course. The premium is larger below median height for men and above median height for young women. The estimates are similar for monozygotic and dizygotic twins, indicating that environmentally and genetically induced height differences are similarly associated with earnings.

The relation between cesarean birth and child cognitive development

This is the first detailed study of the relation between cesarean birth and child cognitive development. We measure differences in child cognitive performance at 4 to 9 years of age between cesarean-born and vaginally-born children (n = 3,666) participating in the Longitudinal Study of Australian Children (LSAC). LSAC is a nationally representative birth cohort surveyed biennially. Using multivariate regression, we control for a large range of confounders related to perinatal risk factors and the socio-economic advantage associated with cesarean-born children. Across several measures, we find that cesarean-born children perform significantly below vaginally-born children, by up to a tenth of a standard deviation in national numeracy test scores at age 8–9. Estimates from a low-risk sub-sample and lower-bound analysis suggest that the relation is not spuriously related to unobserved confounding. Lower rates of breastfeeding and adverse child and maternal health outcomes that are associated with cesarean birth are found to explain less than a third of the cognitive gap, which points to the importance of other mechanisms such as disturbed gut microbiota. The findings underline the need for a precautionary approach in responding to requests for a planned cesarean when there are no apparent elevated risks from vaginal birth.

Educational differences in cardiovascular mortality: The role of shared family factors and cardiovascular risk factors

AIMS

To explore the confounding effects of early family factors shared by siblings and cardiovascular risk factors in midlife on the educational differences in mortality from cardiovascular disease (CVD).

METHODS

Data from national and regional health surveys in Norway (1974-2003) were linked with data from the Norwegian Family Based Life Course Study, the National Educational Registry and the Cause of Death Registry. The study population consisted of participants with at least one full sibling among the health survey participants ( n=271,310). Data were available on CVD risk factors, including weight, height, blood pressure, total cholesterol and smoking.

RESULTS

The hazards ratio (HR) of CVD mortality was 3.44 (95% confidence interval (CI) 2.98-3.96) in the lowest educational group relative to the highest. The HRs were little altered in the within-sibship analyses. Adjusted for risk factors, the HR for CVD mortality in the cohort analyses was 2.05 (CI 1.77-2.37) in the lowest educational group relative to the highest. The respective HR in the within-sibship analyses was 2.46 (CI 1.48-2.24).

CONCLUSIONS

Using a sibling design, we did not find that the association between education and CVD mortality was confounded by early life factors shared by siblings, but it was explained to a large extent by CVD risk factors. These results suggest that reducing levels of CVD risk factors could have the greatest effect on mortality in less well-educated people.

Height, aging and cognitive abilities across Europe

Previous research has found that as a marker of childhood circumstances, height is correlated with cognitive functioning at older ages. Using data from the Survey of Health, Ageing, and Retirement in Europe (SHARE) and about 17,000 respondents from 11 countries, we find that height is positively and significantly associated with cognitive functioning in later life despite controlling for a myriad of possible confounding factors. A 10 cm increase in height is associated with a 0.04 standard deviation increase in a summary cognitive score (mean 0.02, std. dev. 0.77). We find that being born in a country where the infant mortality rate at the time of birth is high has a negative and significant influence on cognitive functioning in later life. A 10% increase in the infant mortality rate is associated with a 0.1 standard deviation decrease in the summary cognitive score. We also find some evidence that height serves as a protective factor against age related deterioration in cognitive functioning. For persons of average stature, age related decreases in cognition scores are 3-5 percentage points smaller if they move up a quartile in the height distribution. Our results also suggest that there is a significant positive association between height and cognitive abilities across countries for this pre-1950 birth cohort of respondents, with correlations ranging from 0.4 to 0.8.

Common genetic variants explain the majority of the correlation between height and intelligence: the generation Scotland study

Greater height and higher intelligence test scores are predictors of better health outcomes. Here, we used molecular (single-nucleotide polymorphism) data to estimate the genetic correlation between height and general intelligence (g) in 6,815 unrelated subjects (median age 57, IQR 49–63) from the Generation Scotland: Scottish Family Health Study cohort. The phenotypic correlation between height and g was 0.16 (SE 0.01). The genetic correlation between height and g was 0.28 (SE 0.09) with a bivariate heritability estimate of 0.71. Understanding the molecular basis of the correlation between height and intelligence may help explain any shared role in determining health outcomes. This study identified a modest genetic correlation between height and intelligence with the majority of the phenotypic correlation being explained by shared genetic influences.

Association of height and violent criminality: results from a Swedish total population study

BACKGROUND

Violent criminality is at least moderately heritable, but the mechanisms behind this remain largely unexplained. Height, a highly heritable trait, may be involved but no study has estimated the effect of height on crime while simultaneously accounting for important demographic, biological and other heritable confounders.

METHODS

We linked nationwide, longitudinal registers for 760 000 men who underwent mandatory military conscription from 1980 through 1992 in Sweden, to assess the association between height and being convicted of a violent crime. We used Cox proportional hazard modelling and controlled for three types of potential confounders: physical characteristics, childhood demographics and general cognitive ability (intelligence).

RESULTS

In unadjusted analyses, height had a moderate negative relationship to violent crime; the shortest of men were twice as likely to be convicted of a violent crime as the tallest. However, when simultaneously controlling for all measured confounders, height was weakly and positively related to violent crime. Intelligence had the individually strongest mitigating effect on the height-crime relationship.

CONCLUSIONS

Although shorter stature was associated with increased risk of violent offending, our analyses strongly suggested that this relationship was explained by intelligence and other confounding factors. Hence, it is unlikely that height, a highly heritable physical characteristic, accounts for much of the unexplained heritability of violent criminality.

The Wilson Effect: The Increase in Heritability of IQ With Age

Ronald Wilson presented the first clear and compelling evidence that the heritability of IQ increases with age. We propose to call the phenomenon ‘The Wilson Effect’ and we document the effect diagrammatically with key twin and adoption studies, including twins reared apart, that have been carried out at various ages and in a large number of different settings. The results show that the heritability of IQ reaches an asymptote at about 0.80 at 18–20 years of age and continuing at that level well into adulthood. In the aggregate, the studies also confirm that shared environmental influence decreases across age, approximating about 0.10 at 18–20 years of age and continuing at that level into adulthood. These conclusions apply to the Westernized industrial democracies in which most of the studies have been carried out.

Adult body height of twins compared with that of singletons: a register-based birth cohort study of Norwegian males

In the present study, we evaluated whether childhood differences in body height between singletons and twins persist into adulthood. Data from the Medical Birth Register of Norway were linked with data from the Norwegian National Conscript Service. This study used data on the 457,999 males who were born alive and without physical anomalies in single or twin births in Norway during 1967-1984 and who were examined at the mandatory military conscription (age 18-20 years; 1985-2003). For sibling comparisons, the authors selected the 1,721 sibships of full brothers that included at least 1 male born in a single birth and at least 1 male born in a twin birth (4,520 persons, including 2,493 twins and 2,027 singletons). An analysis of the total study population using generalized estimating equations showed that the twins were 0.6 cm (95% confidence interval: 0.4, 0.7) shorter than were the singletons after adjustment for a series of background factors. The fixed-effects regression analysis of the sibships that included both twins and singletons showed that the twins were 0.9 cm (95% confidence interval: 0.6, 1.2) shorter than were their singleton brothers. The study suggests that male twins born in Norway during 1967-1984 were slightly shorter in early adulthood than were singletons.

The genetic correlation between height and IQ: shared genes or assortative mating?

Traits that are attractive to the opposite sex are often positively correlated when scaled such that scores increase with attractiveness, and this correlation typically has a genetic component. Such traits can be genetically correlated due to genes that affect both traits ("pleiotropy") and/or because assortative mating causes statistical correlations to develop between selected alleles across the traits ("gametic phase disequilibrium"). In this study, we modeled the covariation between monozygotic and dizygotic twins, their siblings, and their parents (total N = 7,905) to elucidate the nature of the correlation between two potentially sexually selected traits in humans: height and IQ. Unlike previous designs used to investigate the nature of the height-IQ correlation, the present design accounts for the effects of assortative mating and provides much less biased estimates of additive genetic, non-additive genetic, and shared environmental influences. Both traits were highly heritable, although there was greater evidence for non-additive genetic effects in males. After accounting for assortative mating, the correlation between height and IQ was found to be almost entirely genetic in nature. Model fits indicate that both pleiotropy and assortative mating contribute significantly and about equally to this genetic correlation.

Child height, health and human capital: Evidence using genetic markers

Height has long been recognized as being associated with better outcomes: the question is whether this association is causal. We use children's genetic variants as instrumental variables to deal with possible unobserved confounders and examine the effect of child/adolescent height on a wide range of outcomes: academic performance, IQ, self-esteem, depression symptoms and behavioral problems. OLS findings show that taller children have higher IQ, perform better in school, and are less likely to have behavioral problems. The IV results differ: taller girls (but not boys) have better cognitive performance and, in contrast to the OLS, greater height appears to increase behavioral problems.

Twin-singleton differences in intelligence: a register-based birth cohort study of Norwegian males

The aim was to determine the difference in intelligence between singletons and twins in young adulthood. Data from the Medical Birth Register of Norway were linked with register data from the Norwegian National Conscript Service. The study base consisted of data on the 445,463 males who were born alive in either single or twin births in Norway during 1967-1984 and who were examined at the time of the mandatory military conscription (age 18-20). Within this study base, there were data on 1,653 sibships of full brothers that included at least one man born in single birth and at least one man born in twin birth (4,307 persons, including 2,378 twins and 1,929 singletons). The intelligence scores of the singletons were 11% (95% confidence interval [CI]: 9-14%) of a standard deviation higher than those of the twins, after adjustment for birth year, birth order, parental ages at delivery, parental education levels, and other factors. The adjusted within-family difference was also 11% (95 % CI: 6-16%) of a standard deviation, indicating that unmeasured factors shared by siblings (e.g., maternal body height) have not influenced the estimate in important ways. When gestational age at birth was added to the model, the estimate for the difference in intelligence score was approximately the same. Including birth weight in the model strongly reduced the estimate. In conclusion, twins born in Norway during 1967-1984 had slightly lower intelligence in early adulthood compared with the singletons.

Schooling in adolescence raises IQ scores

Although some scholars maintain that education has little effect on intelligence quotient (IQ) scores, others claim that IQ scores are indeed malleable, primarily through intervention in early childhood. The causal effect of education on IQ at later ages is often difficult to uncover because analyses based on observational data are plagued by problems of reverse causation and self-selection into further education. We exploit a reform that increased compulsory schooling from 7 to 9 y in Norway in the 1960s to estimate the effect of education on IQ. We find that this schooling reform, which primarily affected education in the middle teenage years, had a substantial effect on IQ scores measured at the age of 19 y.

The Cognitive Differentiation-Integration Effort Hypothesis: A Synthesis between the Fitness Indicator and Life History Models of Human Intelligence

This article presents a potential synthesis between the fitness indicator and life history models of human intelligence through consideration of the phenomena of ability differentiation and integration. The cognitive differentiation-integration effort hypothesis proposes that these effects result from a life history tradeoff between cognitive integration effort, a mating effort component associated with strengthening the positive manifold amongst abilities; and cognitive differentiation effort, a somatic effort component associated with the cultivation of specific abilities. This represents one of two largely independent sources of genetic variance in intelligence; the other is mediated by general fitness and mutation load and is associated with individual differences in levels of ‘genetic g‘. These two sources (along with a common source of environmental variance) combine to give rise to a variety of cognitive phenotypes characterized by different combinations of high or low levels of ‘genetic g‘ and cognitive specialism or generalism. Fundamental to this model is the assumption that measures of life history speed ( K) and g are essentially independent, which is demonstrated via meta-analysis of 10 studies reporting correlations between the variables (ρ = .023, ns, n = 2056). The implications of the model are discussed in an evolutionary, ecological, and developmental context. Seven key predictions are made in the discussion which if tested could provide definitive evidence for the hypothesis.

On the sources of the height-intelligence correlation: new insights from a bivariate ACE model with assortative mating

A robust positive correlation between height and intelligence, as measured by IQ tests, has been established in the literature. This paper makes several contributions toward establishing the causes of this association. First, we extend the standard bivariate ACE model to account for assortative mating. The more general theoretical framework provides several key insights, including formulas to decompose a cross-trait genetic correlation into components attributable to assortative mating and pleiotropy and to decompose a cross-trait within-family correlation. Second, we use a large dataset of male twins drawn from Swedish conscription records and examine how well genetic and environmental factors explain the association between (i) height and intelligence and (ii) height and military aptitude, a professional psychologist's assessment of a conscript's ability to deal with wartime stress. For both traits, we find suggestive evidence of a shared genetic architecture with height, but we demonstrate that point estimates are very sensitive to assumed degrees of assortative mating. Third, we report a significant within-family correlation between height and intelligence (p^ = 0.10), suggesting that pleiotropy might be at play.

Causes and consequences of early-life health

We examine the consequences of child health for economic and health outcomes in adulthood, using height as a marker of childhood health. After reviewing previous evidence, we present a conceptual framework that highlights data limitations and methodological problems that complicate the study of this topic. We then present estimates of the associations between height and a range of outcomes--including schooling, employment, earnings, health, and cognitive ability--measured in five data sets from early to late adulthood. These results indicate that, on average, taller individuals attain higher levels of education. Height is also positively associated with better economic, health, and cognitive outcomes. These associations are only partially explained by the higher average educational attainment of taller individuals. We then use data from the National Longitudinal Survey of Youth 1979 Children and Young Adults survey to document the associations between health, cognitive development, and growth in childhood. Even among children with the same mother, taller siblings score better on cognitive tests and progress through school more quickly. Part of the differences found between siblings arises from differences in their birth weights and lengths attributable to mother's behaviors while pregnant. Taken together, these results support the hypothesis that childhood health influences health and economic status throughout adulthood.

Requiem for nutrition as the cause of IQ gains: Raven's gains in Britain 1938-2008

The hypothesis that enhanced nutrition is mainly responsible for massive IQ gains over time borrows plausibility from the height gains of the 20th century. However, evidence shows that the two trends are largely independent. A detailed analysis of IQ trends on the Raven's Progressive Matrices tests in Britain dramatizes the poverty of the nutrition hypothesis. A multiple factor hypothesis that operates on three levels is offered as an alternative instrument of causal explanation. The Raven's data show that over the 65 years from circa 1942 to the present, taking ages 5-15 together, British school children have gained 14 IQ points for a rate of 0.216 points per year. However, since 1979, gains have declined with age and between the ages of 12-13 and 14-15, small gains turn into small losses. This is confirmed by Piagetian data and poses the possibility that the cognitive demands of teen-age subculture have been stagnant over perhaps the last 30 years.

Stature and status: Height, ability, and labor market outcomes

The well-known association between height and earnings is often thought to reflect factors such as self esteem, social dominance, and discrimination. We offer a simpler explanation: height is positively associated with cognitive ability, which is rewarded in the labor market. Using data from the US and the UK, we show that taller children have higher average cognitive test scores, and that these test scores explain a large portion of the height premium in earnings. Children who have higher test scores also experience earlier adolescent growth spurts, so that height in adolescence serves as a marker of cognitive ability.

Height at age 18 years is a strong predictor of attained education later in life: cohort study of over 950,000 Swedish men

BACKGROUND

Adult body height has been related to socioeconomic position in cross-sectional studies. Intelligence, shared family factors, and non-familial circumstances may contribute to associations between height and attained education, but their relative importance has been difficult to resolve.

METHODS

A nation-wide record-linkage cohort study of over 950 000 Swedish men born 1950-75 followed with respect to attained education for up to 27 years after measurement of height at age 18 (baseline). The association between height and attained education in later life was investigated by logistic regression modelling with adjustment for age, geography, parental socioeconomic position, and cognitive ability. Shared family factors were accounted for in analyses of full-brother-pairs using conditional logistic regression.

RESULTS

The odds ratio (OR) for attaining higher education 7-27 years after baseline was 1.10 [95% confidence interval (95% CI) 1.09-1.10] in fully adjusted models per 5 cm increase in height. Men taller than 194 cm were two to three times more likely to obtain a higher education as compared with men shorter than 165 cm. The association remained within brother-pairs, OR 1.08 (95% CI 1.07-1.10), suggesting that non-familial factors contribute to the association between height and education attainment. A significant interaction (P < 0.0001) was found between year of birth, height, and attained education, showing slightly weaker associations among later birth cohorts.

CONCLUSIONS

The strong positive association between height and educational achievement remaining after adjustment for year of birth, parental socioeconomic position, other shared family factors, and cognitive ability may reflect educational discrimination based on height although residual confounding cannot be ruled out.