Cognitive epidemiology: Its rise, its current issues, and its challenges

Neuroanatomical norms in the UK Biobank: The impact of allometric scaling, sex, and age

Few neuroimaging studies are sufficiently large to adequately describe population‐wide variations. This study's primary aim was to generate neuroanatomical norms and individual markers that consider age, sex, and brain size, from 629 cerebral measures in the UK Biobank (N = 40,028). The secondary aim was to examine the effects and interactions of sex, age, and brain allometry—the nonlinear scaling relationship between a region and brain size (e.g., total brain volume)—across cerebral measures. Allometry was a common property of brain volumes, thicknesses, and surface areas (83%) and was largely stable across age and sex. Sex differences occurred in 67% of cerebral measures (median |β| = .13): 37% of regions were larger in males and 30% in females. Brain measures (49%) generally decreased with age, although aging effects varied across regions and sexes. While models with an allometric or linear covariate adjustment for brain size yielded similar significant effects, omitting brain allometry influenced reported sex differences in variance. Finally, we contribute to the reproducibility of research on sex differences in the brain by replicating previous studies examining cerebral sex differences. This large‐scale study advances our understanding of age, sex, and brain allometry's impact on brain structure and provides data for future UK Biobank studies to identify the cerebral regions that covary with specific phenotypes, independently of sex, age, and brain size.

Intelligence, health and death

The field of cognitive epidemiology studies the prospective associations between cognitive abilities and health outcomes. We review research in this field over the past decade and describe how our understanding of the association between intelligence and all-cause mortality has consolidated with the appearance of new, population-scale data. To try to understand the association better, we discuss how intelligence relates to specific causes of death, diseases/diagnoses and biomarkers of health through the adult life course. We examine the extent to which mortality and health associations with intelligence might be attributable to people's differences in education, other indicators of socioeconomic status, health literacy and adult environments and behaviours. Finally, we discuss whether genetic data provide new tools to understand parts of the intelligence-health associations. Social epidemiologists, differential psychologists and behavioural and statistical geneticists, among others, contribute to cognitive epidemiology; advances will occur by building on a common cross-disciplinary knowledge base.

Blood pressure and cognitive function across the eighth decade: a prospective study of the Lothian Birth Cohort of 1936

OBJECTIVES

We investigated the associations among blood pressure and cognitive functions across the eighth decade, while accounting for antihypertensive medication and lifetime stability in cognitive function.

DESIGN

Prospective cohort study.

SETTING

This study used data from the Lothian Birth Cohort 1936 (LBC1936) study, which recruited participants living in the Lothian region of Scotland when aged 70 years, most of whom had completed an intelligence test at age 11 years.

PARTICIPANTS

1091 members of the LBC1936 with assessments of cognitive ability in childhood and older adulthood, and blood pressure measurements in older adulthood.

PRIMARY AND SECONDARY OUTCOME MEASURES

Participants were followed up at ages 70, 73, 76 and 79, and latent growth curve models and linear mixed models were used to analyse both cognitive functions and blood pressure as primary outcomes.

RESULTS

Blood pressure followed a quadratic trajectory in the eighth decade: on average blood pressure rose in the first waves and subsequently fell. Intercepts and trajectories were not associated between blood pressure and cognitive functions. Women with higher early-life cognitive function generally had lower blood pressure during the eighth decade. Being prescribed antihypertensive medication was associated with lower blood pressure, but not with better cognitive function.

CONCLUSIONS

Our findings indicate that women with higher early-life cognitive function had lower later-life blood pressure. However, we did not find support for the hypothesis that rises in blood pressure and worse cognitive decline are associated with one another in the eighth decade.

Hypertension Development by Midlife and the Roles of Premorbid Cognitive Function, Sex, and Their Interaction

Higher early-life cognitive function is associated with better later-life health outcomes, including hypertension. Associations between higher prior cognitive function and less hypertension persist even when accounting for socioeconomic status, but socioeconomic status-hypertension gradients are more pronounced in women. We predicted that differences in hypertension development between sexes might be associated with cognitive function and its interaction with sex, such that higher early-life cognitive function would be associated with lower hypertension risk more in women than in men. We used accelerated failure time modeling with the National Longitudinal Study of Youth 1979. Cognitive function was assessed in youth, when participants were aged between 14 and 21 years. Of 2572 men and 2679 women who completed all assessments, 977 men and 940 women reported hypertension diagnoses by 2015. Socioeconomic status in youth and adulthood were investigated as covariates, as were components of adult socioeconomic status: education, occupational status, and family income. An SD of higher cognitive function in youth was associated with reduced hypertension risk (acceleration factor: ĉ=0.97; 95% CI, 0.96-0.99; P=0.001). The overall effect was stronger in women (sex×cognitive function: ĉ=0.97; 95% CI, 0.94-0.99; P=0.010); especially, higher functioning women were less at risk than their male counterparts. This interaction was itself attenuated by a sex by family income interaction. People with better cognitive function in youth, especially women, are less likely to develop hypertension later in life. Income differences accounted for these associations. Possible causal explanations are discussed.

Are Psycho-Behavioral Factors Accounting for Longevity?

The general objective of this article is to critically review the state of the art regarding current factors accounting for aging, longevity and successful longevity. There are two major constructs which most authors are employing to account for longevity: genetic or intrinsic components versus environmental or extrinsic factors. This classification has important flaws: (i) From an epigenetic standpoint, such a polar classification could lead to misconceptions since both factors are interdependent through lifelong interactions. (ii) There are no specifications regarding these “environmental” factors, which include a broad heterogeneity of conditions (physical, economic, social, and cultural aspects as well as behavioral ones such as lifestyle) but do not include personal conditions, such as psychological characteristics. The review of the new paradigm called successful aging yields an important set of psycho-behavioral factors, and although population indexes such as Disability Free Life Expectancy (DFLE) or Healthy Life expectancy (HLE) have been developed, authors do not take into consideration healthy or successful longevity as a potential prolongation of the new paradigm of active or successful aging. There is a broad corpus of research literature supporting the importance of psycho-behavioral (PB) factors intervening in the ways of aging, specifically intelligence and cognitive functioning, positive emotion and control, personality traits, psychosocial, physical conditions, and lifestyles, all of which are highly associated with active aging, health, longevity, and survival. The importance of these factors accounting for longevity, and successful longevity must be taken into consideration as a pending issue in gerontology.

Discovering markers of healthy aging: a prospective study in a Danish male birth cohort

There is a pressing need to identify markers of cognitive and neural decline in healthy late-midlife participants. We explored the relationship between cross-sectional structural brain-imaging derived phenotypes (IDPs) and cognitive ability, demographic, health and lifestyle factors (non-IDPs). Participants were recruited from the 1953 Danish Male Birth Cohort (N=193). Applying an extreme group design, members were selected in 2 groups based on cognitive change between IQ at age ~20y (IQ-20) and age ~57y (IQ-57). Subjects showing the highest (n=95) and lowest (n=98) change were selected (at age ~57) for assessments on multiple IDPs and non-IDPs. We investigated the relationship between 453 IDPs and 70 non-IDPs through pairwise correlation and multivariate canonical correlation analysis (CCA) models. Significant pairwise associations included positive associations between IQ-20 and gray-matter volume of the temporal pole. CCA identified a richer pattern - a single "positive-negative" mode of population co-variation coupling individual cross-subject variations in IDPs to an extensive range of non-IDP measures (r = 0.75, P_corrected < 0.01). Specifically, this mode linked higher cognitive performance, positive early-life social factors, and mental health to a larger brain volume of several brain structures, overall volume, and microstructural properties of some white matter tracts. Interestingly, both statistical models identified IQ-20 and gray-matter volume of the temporal pole as important contributors to the inter-individual variation observed. The converging patterns provide novel insight into the importance of early adulthood intelligence as a significant marker of late-midlife neural decline and motivates additional study.

Childhood IQ predicts age-38 oral disease experience and service-use

OBJECTIVES

Given that people with higher intelligence have been shown to live longer, enjoy better health and have more favourable health behaviours, we investigated the association between childhood IQ and a range of important dental health and service-use indicators at age 38.

METHODS

Long-standing prospective study of a complete birth cohort, with childhood IQ (assessed at ages 7, 9, 11 and 13 years) used to allocate participants (N = 818) to one of four ordinal categories of childhood IQ.

RESULTS

There were distinct and consistent gradients by childhood IQ in almost all of the dental caries experience measures (with the exception of filled teeth) whereby each was most severe in the lowest child IQ category and least severe in the highest; the exception was the mean FT score, for which there was no discernible gradient. Indicators of self-care and periodontal disease experience showed similar gradients, and multivariate modelling using the continuous IQ score confirmed the observed patterns.

CONCLUSIONS

Childhood cognitive function is a key determinant of oral health and dental service-use by midlife, with those of lower cognitive capacity as children likely to have poorer oral health, less favourable oral health-related beliefs, and more detrimental self-care and dental visiting practices by age 38. There is a need to shape dental clinical services and public health interventions so that people with the poorest cognitive function do not continue to be disadvantaged.

What genome-wide association studies reveal about the association between intelligence and physical health, illness, and mortality

The associations between higher intelligence test scores from early life and later good health, fewer illnesses, and longer life are recent discoveries. Researchers are mapping the extent of these associations and trying to understanding them. Part of the intelligence-health association has genetic origins. Recent advances in molecular genetic technology and statistical analyses have revealed that: intelligence and many health outcomes are highly polygenic; and that modest but widespread genetic correlations exist between intelligence and health, illness and mortality. Causal accounts of intelligence-health associations are still poorly understood. The contribution of education and socio-economic status - both of which are partly genetic in origin - to the intelligence-health associations are being explored.

Healthy cognitive ageing in the Lothian Birth Cohort studies: marginal gains not magic bullet

In the face of shifting demographics and an increase in human longevity, it is important to examine carefully what is known about cognitive ageing, and to identify and promote possibly malleable lifestyle and health-related factors that might mitigate age-associated cognitive decline. The Lothian Birth Cohorts of 1921 (LBC1921, n = 550) and 1936 (LBC1936, n = 1091) are longitudinal studies of cognitive and brain ageing based in Scotland. Childhood IQ data are available for these participants, who were recruited in later life and then followed up regularly. This overview summarises some of the main LBC findings to date, illustrating the possible genetic and environmental contributions to cognitive function (level and change) and brain imaging biomarkers in later life. Key associations include genetic variation, health and fitness, psychosocial and lifestyle factors, and aspects of the brain's structure. It addresses some key methodological issues such as confounding by early-life intelligence and social factors and emphasises areas requiring further investigation. Overall, the findings that have emerged from the LBC studies highlight that there are multiple correlates of cognitive ability level in later life, many of which have small effects, that there are as yet few reliable predictors of cognitive change, and that not all of the correlates have independent additive associations. The concept of marginal gains, whereby there might be a cumulative effect of small incremental improvements across a wide range of lifestyle and health-related factors, may offer a useful way to think about and promote a multivariate recipe for healthy cognitive and brain ageing.

Exploring the relationship between video game expertise and fluid intelligence

Hundreds of millions of people play intellectually-demanding video games every day. What does individual performance on these games tell us about cognition? Here, we describe two studies that examine the potential link between intelligence and performance in one of the most popular video games genres in the world (Multiplayer Online Battle Arenas: MOBAs). In the first study, we show that performance in the popular MOBA League of Legends’ correlates with fluid intelligence as measured under controlled laboratory conditions. In the second study, we also show that the age profile of performance in the two most widely-played MOBAs (League of Legends and DOTA II) matches that of raw fluid intelligence. We discuss and extend previous videogame literature on intelligence and videogames and suggest that commercial video games can be useful as 'proxy' tests of cognitive performance at a global population level.

Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947

OBJECTIVE

To extend previous literature that suggests higher IQ in youth is associated with living longer. Previous studies have been unable to assess reliably whether the effect differs across sexes and ages of death, and whether the effect is graded across different levels of IQ.

METHODS

We test IQ-survival associations in 94% of the near-entire population born in Scotland in 1936 who took an IQ test at age 11 (n = 70,805) and were traced in a 68-year follow-up.

RESULTS

Higher IQ at age 11 years was associated with a lower risk of death (HR = 0.80, 95% CI = 0.79, 0.81). The decline in risk across categories of IQ scores was graded across the full range with the effect slightly stronger in women (HR = 0.79, 95% CI = 0.77, 0.80) than in men (HR = 0.82, 95% CI = 0.81, 0.84). Higher IQ had a significantly stronger association with death before and including age 65 (HR = 0.76, 95% CI = 0.74, 0.77) than in those participants who died at an older age (HR = 0.79, 95% CI = 0.78, 0.80).

CONCLUSIONS

Higher childhood IQ is associated with lower risk of all-cause mortality in both men and women. This is the only near-entire population study to date that examines the association between childhood IQ and mortality across most of the human life course.

Shared genetic aetiology between cognitive functions and physical and mental health in UK Biobank (N=112 151) and 24 GWAS consortia

Causes of the well-documented association between low levels of cognitive functioning and many adverse neuropsychiatric outcomes, poorer physical health and earlier death remain unknown. We used linkage disequilibrium regression and polygenic profile scoring to test for shared genetic aetiology between cognitive functions and neuropsychiatric disorders and physical health. Using information provided by many published genome-wide association study consortia, we created polygenic profile scores for 24 vascular-metabolic, neuropsychiatric, physiological-anthropometric and cognitive traits in the participants of UK Biobank, a very large population-based sample (N=112 151). Pleiotropy between cognitive and health traits was quantified by deriving genetic correlations using summary genome-wide association study statistics and to the method of linkage disequilibrium score regression. Substantial and significant genetic correlations were observed between cognitive test scores in the UK Biobank sample and many of the mental and physical health-related traits and disorders assessed here. In addition, highly significant associations were observed between the cognitive test scores in the UK Biobank sample and many polygenic profile scores, including coronary artery disease, stroke, Alzheimer's disease, schizophrenia, autism, major depressive disorder, body mass index, intracranial volume, infant head circumference and childhood cognitive ability. Where disease diagnosis was available for UK Biobank participants, we were able to show that these results were not confounded by those who had the relevant disease. These findings indicate that a substantial level of pleiotropy exists between cognitive abilities and many human mental and physical health disorders and traits and that it can be used to predict phenotypic variance across samples.

Neonatal treatment philosophy in Dutch and German NICUs: health-related quality of life in adulthood of VP/VLBW infants

PURPOSE

Although survival after very preterm birth (VP)/very low birth weight (VLBW) has improved, a significant number of VP/VLBW individuals develop physical and cognitive problems during their life course that may affect their health-related quality of life (HRQoL). We compared HRQoL in VP/VLBW cohorts from two countries: The Netherlands (n = 314) versus Germany (n = 260) and examined whether different neonatal treatment and rates of disability affect HRQoL in adulthood.

METHOD

To analyse whether cohorts differed in adult HRQoL, linear regression analyses were performed for three HRQoL outcomes assessed with the Health Utilities Index 3 (HUI3), the London Handicap Scale (LHS), and the WHO Quality of Life instrument (WHOQOL-BREF). Stepwise hierarchical linear regression was used to test whether neonatal physical health and treatment, social environment, and intelligence (IQ) were related to VP/VLBW adults' HRQoL and cohort differences.

RESULTS

Dutch VP/VLBW adults reported a significantly higher HRQoL on all three general HRQoL measures than German VP/VLBW adults (HUI3: .86 vs .83, p = .036; LHS: .93 vs. .90, p = .018; WHOQOL-BREF: 82.8 vs. 78.3, p < .001). Main predictor of cohort differences in all three HRQoL measures was adult IQ (p < .001).

CONCLUSIONS

Lower HRQoL in German versus Dutch adults was related to more cognitive impairment in German adults. Due to different policies, German VP/VLBW infants received more intensive treatment that may have affected their cognitive development. Our findings stress the importance of examining effects of different neonatal treatment policies for VP/VLBW adults' life.

Preterm Cognitive Function Into Adulthood

BACKGROUND

Very preterm (VP; gestational age <32 weeks) and very low birth weight (VLBW; <1500 g) births are related to impaired cognitive function across the life span. It is not known how stable cognitive functions are from childhood to adulthood for VP/VLBW compared with term-born individuals and how early adult cognitive function can be predicted.

METHODS

The Bavarian Longitudinal Study is a prospective geographically defined cohort study that followed 260 VP/VLBW and 229 term-born individuals from birth to adulthood. Data on cognitive function were assessed with developmental and IQ tests at 5 and 20 months and at 4, 6, 8, and 26 years of age.

RESULTS

Across all assessments, VP/VLBW individuals had significantly lower IQ scores than term-born controls, even when individuals with severe cognitive impairment (n = 69) were excluded. IQ scores were found to be more stable over time for VP/VLBW than term-born individuals, yet differences in stability disappeared when individuals with cognitive impairment were excluded. Adult IQ could be predicted with fair certainty (r > 0.50) from age 20 months onward for the whole VP/VLBW sample (n = 260) and from 6 years onward for term-born individuals (n = 229).

CONCLUSIONS

VP/VLBW individuals more often suffer from cognitive problems across childhood into adulthood and these problems are relatively stable from early childhood onward. VP/VLBW children's risk for cognitive problems can be reliably diagnosed at the age of 20 months. These findings provide strong support for the timing of cognitive follow-up at age 2 years to plan special support services for children with cognitive problems.

Early-Life Intelligence Predicts Midlife Biological Age

OBJECTIVES

Early-life intelligence has been shown to predict multiple causes of death in populations around the world. This finding suggests that intelligence might influence mortality through its effects on a general process of physiological deterioration (i.e., individual variation in "biological age"). We examined whether intelligence could predict measures of aging at midlife before the onset of most age-related disease.

METHODS

We tested whether intelligence assessed in early childhood, middle childhood, and midlife predicted midlife biological age in members of the Dunedin Study, a population-representative birth cohort.

RESULTS

Lower intelligence predicted more advanced biological age at midlife as captured by perceived facial age, a 10-biomarker algorithm based on data from the National Health and Nutrition Examination Survey (NHANES), and Framingham heart age (r = 0.1-0.2). Correlations between intelligence and telomere length were less consistent. The associations between intelligence and biological age were not explained by differences in childhood health or parental socioeconomic status, and intelligence remained a significant predictor of biological age even when intelligence was assessed before Study members began their formal schooling.

DISCUSSION

These results suggest that accelerated aging may serve as one of the factors linking low early-life intelligence to increased rates of morbidity and mortality.

Prenatal exposure to polycyclic aromatic hydrocarbons and cognitive dysfunction in children

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by combustion of fossil fuel and other organic materials. Both experimental animal and human studies have reported the harmful impacts of PAH compounds on fetal growth and neurodevelopment, including verbal IQ of children. Here, we have assessed the association between cognitive function of children and prenatal PAH exposures. The study is part of an ongoing, longitudinal investigation of the health effects of prenatal exposure to air pollution on infants and children in Krakow, Poland. The subjects in this report included 170 children whose mothers were enrolled to the study in the first or second trimester of pregnancy whose cord blood were tested for PAH-DNA adducts and who were assessed at age 7 using the Wechsler Intelligence Scale for Children-Revised (WISC-R). The outcome of a priori interest was depressed verbal IQ index (DepVIQ), which is the difference between WISC-R performance and verbal IQ scores. Prenatal PAH exposure was measured by cord blood PAH-DNA adducts, an individual dosimeter, integrating exposure from various sources of exposure over the gestational period. The estimated effect of prenatal PAH exposure on cognitive function was adjusted in multivariable regression for a set of potential confounders (child's gender, parity, maternal education, breastfeeding practice, environmental tobacco smoke (ETS), and postnatal PAH exposure). The prevalence of DepVIQ was significantly higher in children with detectable PAH-DNA adducts compared to those with undetectable adducts (13.7 vs. 4.4 %,). Binary multivariable regression documented that the relative risk of DepVIQ increased threefold with a ln-unit increase in cord blood adducts (relative risk (RR) = 3.0, 95 % confidence interval (CI) 1.3-6.8). Postnatal PAH exposure also increased the risk of DepVIQ (RR = 1.6, 95 % CI 1.1-2.5). Long-term exclusive breastfeeding (at least 6 months) showed a protective effect (RR = 0.3, 95 % CI 0.1-0.9). In conclusion, these results provide further evidence that PAHs are harmful to the developing fetal brain with effects extending through childhood, with implications for the academic success of the children.

Does high intelligence improve prognosis? The association of intelligence with recurrence and mortality among Swedish men with coronary heart disease

BACKGROUND

Lower intelligence early in life is associated with increased risks for coronary heart disease (CHD) and mortality. Intelligence level might affect compliance to treatment but its prognostic importance in patients with CHD is unknown.

METHODS

A cohort of 1923 Swedish men with a measure of intelligence from mandatory military conscription in 1969-1970 at age 18-20, who were diagnosed with CHD 1991-2007, were followed to the end of 2008.

PRIMARY OUTCOME

recurrent CHD event. Secondary outcome: case fatality from the first event, cardiovascular and all-cause mortality. National registers provided information on CHD events, comorbidity, mortality and socioeconomic factors.

RESULTS

The fully adjusted HRs for recurrent CHD for medium and low intelligence, compared with high intelligence, were 0.98, (95% CIs 0.83 to 1.16) and 1.09 (0.89 to 1.34), respectively. The risks were increased for cardiovascular and all-cause mortality with lower intelligence, but were attenuated in the fully adjusted models (fully adjusted HRs for cardiovascular mortality 1.92 (0.94 to 3.94) and 1.98 (0.89 to 4.37), respectively; for all-cause mortality 1.63 (1.00 to 2.65) and 1.62 (0.94 to 2.78), respectively). There was no increased risk for case-fatality at the first event (fully adjusted ORs 1.06 (0.73 to 1.55) and 0.97 (0.62 to 1.50), respectively).

CONCLUSIONS

Although we found lower intelligence to be associated with increased mortality in middle-aged men with CHD, there was no evidence for its possible effect on recurrence in CHD.

Retinal vessel caliber and lifelong neuropsychological functioning: retinal imaging as an investigative tool for cognitive epidemiology

Why do more intelligent people live healthier and longer lives? One possibility is that intelligence tests assess health of the brain, but psychological science has lacked technology to evaluate this hypothesis. Digital retinal imaging, a new, noninvasive method to visualize microcirculation in the eye, may reflect vascular conditions in the brain. We studied the association between retinal vessel caliber and neuropsychological functioning in the representative Dunedin birth cohort. Wider venular caliber was associated with poorer neuropsychological functioning at midlife, independently of potentially confounding factors. This association was not limited to any specific test domain and extended to informants' reports of cohort members' cognitive difficulties in everyday life. Moreover, wider venular caliber was associated with lower childhood IQ tested 25 years earlier. The findings indicate that retinal venular caliber may be an indicator of neuropsychological health years before the onset of dementing diseases and suggest that digital retinal imaging may be a useful investigative tool for psychological science.

Personality is of central concern to understand health: towards a theoretical model for health psychology

This paper sets out the case that personality traits are central to health psychology. To achieve this, three aims need to be addressed. First, it is necessary to show that personality influences a broad range of health outcomes and mechanisms. Second, the simple descriptive account of Aim 1 is not sufficient, and a theoretical specification needs to be developed to explain the personality-health link and allow for future hypothesis generation. Third, once Aims 1 and 2 are met, it is necessary to demonstrate the clinical utility of personality. In this review I make the case that all three Aims are met. I develop a theoretical framework to understand the links between personality and health drawing on current theorising in the biology, evolution, and neuroscience of personality. I identify traits (i.e., alexithymia, Type D, hypochondriasis, and empathy) that are of particular concern to health psychology and set these within evolutionary cost-benefit analysis. The literature is reviewed within a three-level hierarchical model (individual, group, and organisational) and it is argued that health psychology needs to move from its traditional focus on the individual level to engage group and organisational levels.

Looking for 'system integrity' in cognitive epidemiology

BACKGROUND

In the last decade, an increasing body of empirical evidence has gathered to establish an association between higher cognitive ability in youth and later mortality, less morbidity and better health. This field of research is known as cognitive epidemiology. The causes of these associations are not understood.

OBJECTIVE

Among the possible explanations for the associations is the suggestion that they might, in part, be accounted for by general bodily 'system integrity'. That is, scoring well on cognitive ability tests might be an indicator of a more general tendency for complex systems in the body to be efficient. The construct of system integrity is critically assessed.

METHOD

This viewpoint provides a critical presentation and an empirical and theoretical evaluation of the construct of system integrity as it is used in cognitive epidemiology.

RESULTS

A precedent of the system integrity suggestion is discovered. The empirical tests of the system integrity idea to date are critically evaluated. Other possible routes to testing system integrity are suggested. There is a critical re-evaluation of the idea and other, related concepts.

CONCLUSION

The construct of system integrity is distinct from related constructs. It is still underdeveloped theoretically, and undertested empirically within cognitive epidemiology.

Effect of exclusive breastfeeding on the development of children's cognitive function in the Krakow prospective birth cohort study

The main goal of the study was to assess the effect of exclusive breastfeeding on the neurodevelopment of children over a 7-year follow-up period and to test the hypothesis that the observed cognitive gain in breastfed children in the first years of life is a strong predictor of their cognitive development trajectory, which may be continued in later life. The analysis is based on data from the 7-year follow-up of 468 term babies (>36 weeks of gestation) born to non-smoking mothers participating in an ongoing prospective cohort study. The cognitive function of children was assessed by psychometric tests performed five times at regular intervals from infancy through the preschool age. The study included valid neurodevelopmental assessment of the children-443 participants were evaluated least twice; 425, three times; and 307, five times in the follow-up period. The association between the cognitive achievements of preschool age children and exclusive breastfeeding of various durations was performed using the generalized estimating equation longitudinal model, adjusted for major confounders such as maternal education, gender, parity, and weight gain in pregnancy. Children breastfed exclusively for up to 3 months had intelligence quotients (IQs) that were on average 2.1 points higher compared to the others (95% confidence interval (CI), 0.24-3.9); children breastfed for 4-6 months scored higher by 2.6 points (95% CI, 0.87-4.27); and the benefit for children breastfed even longer (>6 months) increased by 3.8 points (95% CI, 2.11-5.45). Other predictors were maternal education, gender of the child, having an older sibling, and weight gain during pregnancy. The results of the study support the WHO expert recommendations on exclusive breastfeeding for 6 months; moreover, they provide evidence that even a shorter duration of exclusive breastfeeding in early infancy produces beneficial effects on the cognitive development of children. The breastfeeding-related IQ gain observed already at the age of 1 was sustained through preschool age, and the difference in terms of IQ score between breastfed children and the reference group (mixed breastfeeding) held constant over the whole preschool period.

Cognitive function of 6-year old children exposed to mold-contaminated homes in early postnatal period. Prospective birth cohort study in Poland

In the last decade, the neurologic effects of various air pollutants have been the focus of increasing attention. The main purpose of this study was to assess the potential impact of early childhood exposure to indoor molds on the subsequent cognitive function of 6-year old children. The results of this study are based on the six-year follow-up of 277 babies born at term to mothers participating in a prospective cohort study in Krakow, Poland. The study participants are all non-smoking pregnant women who were free of chronic diseases such as diabetes and hypertension. The presence of visible mold patches on indoor walls was monitored at regular time intervals over gestation and after birth up to the age of five. The Wechsler Intelligence Scale for Children (WISC-R) was administered to children at age 6. The exposure effect of living in mold-contaminated homes on the IQ scores of children was adjusted for major confounders, known to be important for the cognitive development of children such as maternal education, the child's gender, breastfeeding practices in infancy, the presence of older siblings and the prenatal exposure to lead and environmental tobacco smoke (ETS). The adjusted IQ deficit attributed to longer exposures to indoor molds (>2 years) was significantly lower on the IQ scale (beta coeff.=-9.16, 95%CI: -15.21, -3.10) and tripled the risk of low IQ scoring (OR=3.53; 95%CI: 1.11-11.27) compared with references. While maternal education (beta coeff.=0.61, 95%CI: 0.05, 1.17) and breastfeeding (beta coeff.=4.0; 95%CI: 0.84, 7.17) showed a significant positive impact on cognitive function, prenatal ETS exposure (beta coeff.=-0.41; 95%CI: -0.79, -0.03) and the presence of older siblings (beta coefficient=-3.43; 95%CI: -5.67, -1.20) were associated with poorer cognitive function in children. In conclusion, the results of this study draw attention to the harmful effect of early postnatal exposure to indoor molds on children's cognitive development and provide additional evidence on the role of environmental determinants in human cognitive development.

Adolescent IQ and survival in the Wisconsin longitudinal study

OBJECTIVE

This study attempts to explain the ubiquitous positive correlation between cognitive ability (IQ) and survival.

METHODS

A sample of 10,317 Wisconsin high school graduates of 1957 was followed until 2009, from ages 18 to 68 years. Mortality was analyzed using a Weibull survival model that includes gender, social background, Henmon-Nelson IQ, and rank in high school class.

RESULTS

Rank in high school class, a cumulative measure of responsible performance during high school, entirely mediates the relationship between adolescent IQ and survival. Its effect on survival is 3 times greater than that of IQ, and it accounts for about 10% of the female advantage in survival.

DISCUSSION

Cognitive functioning may improve survival by promoting responsible and timely patterns of behavior that are firmly in place by late adolescence. Prior research suggests that conscientiousness, one of the "Big Five" personality characteristics, plays a key role in this relationship.