G. David Batty

Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis

Abstract Objective To assess the importance of maternal intelligence, and the effect of controlling for it and other important confounders, in the link between breast feeding and childrens intelligence. Design Examination of the effect of breast feeding on cognitive ability and the impact of a range of potential confounders, in particular maternal IQ, within a national database. Additional analyses compared pairs of siblings from the sample who were and were not breast fed. The results are considered in the context of other studies that have also controlled for parental intelligence via meta-analysis. Setting 1979 US national longitudinal survey of youth. Subjects Data on 5475 children, the offspring of 3161 mothers in the longitudinal survey. Main outcome measure IQ in children measured by Peabody individual achievement test. Results The mothers IQ was more highly predictive of breastfeeding status than were her race, education, age, poverty status, smoking, the home environment, or the childs birth weight or birth order. One standard deviation advantage in maternal IQ more than doubled the odds of breast feeding. Before adjustment, breast feeding was associated with an increase of around 4 points in mental ability. Adjustment for maternal intelligence accounted for most of this effect. When fully adjusted for a range of relevant confounders, the effect was small (0.52) and non-significant (95% confidence interval −0.19 to 1.23). The results of the sibling comparisons and meta-analysis corroborated these findings. Conclusions Breast feeding has little or no effect on intelligence in children. While breast feeding has many advantages for the child and mother, enhancement of the childs intelligence is unlikely to be among them.

Intelligence and Personality as Predictors of Illness and Death How Researchers in Differential Psychology and Chronic Disease Epidemiology Are Collaborating to Understand and Address Health Inequalities

This monograph describes research findings linking intelligence and personality traits with health outcomes, including health behaviors, morbidity, and mortality. The field of study of intelligence and health outcomes, is called cognitive epidemiology, and the field of study of personality traits and health outcomes is known as personological epidemiology. Intelligence and personality traits are the principal research topics studied by differential psychologists, so the combined field could be called differential epidemiology. This research is important for the following reasons: The findings overviewed are relatively new, and many researchers and practitioners are unaware of them; the effect sizes are on par with better-known, traditional risk factors for illness and death; mechanisms of the associations are largely unknown, so they must be explored further; and the findings have yet to be applied, so we write this to encourage diverse interested parties to consider how applications might be achieved. To make this research accessible to as many relevant researchers, practitioners, policymakers, and laypersons as possible, we first provide an overview of the basic discoveries regarding intelligence and personality. We describe the nature and structure of the measured phenotypes (i.e., the observable characteristics of an individual) in both fields. Although both areas of study are well established, we recognize that this may not be common knowledge outside of experts in the field. Human intelligence differences are described by a hierarchy that includes general intelligence (g) at the pinnacle, strongly correlated broad domains of cognitive functioning at a lower level, and specific abilities at the foot. The major human differences in personality are described by five personality factors that are widely agreed on with respect to their number and nature: neuroticism, extraversion, openness, agreeableness, and conscientiousness. As a foundation for health-related findings, we provide a summary of research showing that intelligence and personality differences can be measured reliably and validly and are stable across many years (even decades), substantially heritable, and related to important life outcomes. Cognitive and personality traits are fundamental aspects of a person, and they have relevance to life chances and outcomes, including health outcomes. We provide an overview of major and recent research on the associations between intelligence and personality traits and health outcomes. These outcomes include mortality from all causes, specific causes of death, specific illnesses, and others, such as health-related behaviors. Intelligence and personality traits are significantly and substantially (by comparison with traditional risk factors) related to all of these outcomes. The studies we describe are unusual in psychology: They have large sample sizes (typically thousands of subjects, sometimes ~1 million), the samples are more representative of the background population than in most studies, the follow-up times are long (sometimes many decades, almost the whole human life span), and the outcomes are objective health measures (including death), not just self-reports. In addition to the associations, possible mechanisms for the associations are described and discussed, and some attempts to test these mechanisms are illustrated. It is relatively early in this research field, so a significant amount of work remains to be done. Finally, we make some preliminary remarks about possible applications, with the knowledge that the psychological predictors addressed are somewhat stable aspects of the person, with substantial genetic causes. Nevertheless, we believe differential epidemiology can be a useful component of interventions to improve individual and public health. Intelligence and personality differences are possible causes of later health inequalities; the eventual aim of cognitive and personological epidemiology is to reduce or eliminate these inequalities, to the extent that it is possible, and provide information to help people toward their own optimal health through the life course. We present these findings to a wider audience so that more associations will be explored, a better understanding of the mechanisms of health inequalities will be produced, and inventive applications will follow on the basis of what we hope will be seen as practically useful knowledge.

Height, wealth, and health: An overview with new data from three longitudinal studies

This overview, based on a literature review and new data from the three cohorts (Whitehall Studies I and II, and the Vietnam Experience Study), has four objectives: (a) to outline the major determinants of height, so providing an indication as to what exposures this characteristic may capture; (b) to summarise, by reviewing reports from large scale studies, the relation between adult height and a range of disease outcomes--both somatic and psychiatric--with particular emphasis on coronary heart disease (CHD) and stroke; (c) to discuss why these relationships may exist, in particular, the role, if any, of socioeconomic position in explaining the apparent associations; and, finally (d) to outline future research directions in this field. The large majority of evidence for predictors of height, and its health consequences, comes from observational studies. While genetic predisposition is a major determinant of height, secular rises in childhood and adult stature across successive birth cohorts suggest that early life environment also has an important impact. Plausible non-genetic determinants of height include nutrition, illness, socioeconomic status, and psychosocial stress. Evidence for an association between height and a series of health endpoints is accumulating. Thus, shorter people appear to experience increased risk of CHD, and these associations appear to be independent of socioeconomic position and other potentially confounding variables. For stroke, and its sub-types, findings are less clear. In contrast to CHD, some cancers, such as carcinoma of the colorectum, prostate, breast (in women), central nervous system, skin, endometrium, thyroid and blood (haematopoietic) are more common in taller people. While height may be negatively related to the risk of completed suicide, conclusions about the links between stature and other health endpoints is problematic given the paucity of evidence, which should be addressed. Ultimately, for want of better data, investigators in this area have used height as a proxy for a range of pre-adult exposures. In future, research should aim to explore the predictive capacity of direct measures of diet, psychosocial stress, childhood chronic illness and so on, rather than focus on height or its components. The problem is that extended follow-up of child cohorts with such data are required, and studies which hold these data are not currently available, although several are either maturing to the point where they offer sufficient clinical outcomes to facilitate analyses or are in the advanced planning stage.

Effect of body mass index and alcohol consumption on liver disease: analysis of data from two prospective cohort studies

Objective To investigate whether alcohol consumption and raised body mass index (BMI) act together to increase risk of liver disease. Design Analysis of data from prospective cohort studies. Setting Scotland. Participants Data were from two of the Midspan prospective cohort studies (9559 men): “Main” study 1965-8, participants from workplaces across central belt of Scotland, population of island of Tiree, and mainland relatives, and “Collaborative” study, 1970-3, participants from 27 workplaces in Glasgow, Clydebank, and Grangemouth. Follow-up was to 31 December 2007 (median 29 years, range 0.13-42). We divided participants into nine groups based on measures of body mass index (BMI) (underweight/normal weight <25, overweight 25 to <30, and obese ≥30) and alcohol consumption (none, 1-14, and ≥15 units per week). Main outcome measures Liver disease morbidity and mortality. Results 80 (0.8%) men died with liver disease as the main cause and 146 (1.5%) with liver disease as any cause. In the Collaborative study, 196 men (3.3%) had liver disease defined by a death, admission, or cancer registration. BMI and alcohol consumption were strongly associated with liver disease mortality in analyses adjusted for other confounders (P=0.001 and P<0.0001 respectively). Drinkers of 15 or more units per week in any BMI category and obese drinkers had raised relative rates for all definitions of liver disease, compared with underweight/normal weight non-drinkers. Drinkers of 15 or more units per week had adjusted relative rates for liver disease mortality of 3.16 (95% confidence interval 1.28 to 7.8) for underweight/normal weight men, 7.01 (3.02 to 16.3) for overweight, and 18.9 (6.84 to 52.4) for obese men. The relative rate for obese men who consumed 1-14 units per week was 5.3 (1.36 to 20.7). The relative excess risk due to interaction between BMI and alcohol consumption was 5.58 (1.09 to 10.1); synergy index=2.89 (1.29 to 6.47). Conclusions Raised BMI and alcohol consumption are both related to liver disease, with evidence of a supra-additive interaction between the two. The occurrence of both factors in the same populations should inform health promotion and public health policies.

Bright Children Become Enlightened Adults

We examined the prospective association between general intelligence (g) at age 10 and liberal and antitraditional social attitudes at age 30 in a large (N = 7,070), representative sample of the British population born in 1970. Statistical analyses identified a general latent trait underlying attitudes that are antiracist, proworking women, socially liberal, and trusting in the democratic political system. There was a strong association between higher g at age 10 and more liberal and antitraditional attitudes at age 30; this association was mediated partly via educational qualifications, but not at all via occupational social class. Very similar results were obtained for men and women. People in less professional occupations—and whose parents had been in less professional occupations—were less trusting of the democratic political system. This study confirms social attitudes as a major, novel field of adult human activity that is related to childhood intelligence differences.

Generalized anxiety disorder, major depressive disorder, and their comorbidity as predictors of all-cause and cardiovascular mortality: the Vietnam experience study.

Objective: To examine whether the 1-year prevalence of major depressive disorder (MDD), generalized anxiety disorder (GAD), and their comorbidity were associated with subsequent all-cause and cardiovascular disease (CVD) mortality during 15 years in Vietnam veterans. Methods: Participants (N = 4256) were from the Vietnam Experience Study. Service, sociodemographic, and health data were collected from service files, telephone interviews, and a medical examination. One-year prevalence of MDD and GAD was determined through a diagnostic interview schedule based on the Diagnostic and Statistical Manual of Mental Disorders (version IV) criteria. Mortality over the subsequent 15 years was gathered from US army records. Results: MDD and GAD were positively and significantly associated with all-cause and CVD mortality. The relationships between MDD and GAD and CVD mortality were no longer significant after adjustment for sociodemograhics, health status at entry, health behaviors, and other risk markers. Income was the covariate with the strongest impact on this association. In analyses comparing comorbidity and GAD and MDD alone, with neither diagnosis, comorbidity proved to be the strongest predictor of both all-cause and CVD mortality. Conclusion: GAD and MDD predict all-cause mortality in a veteran population after adjusting for a range of covariates. However, those with both GAD and MDD were at greatest risk of subsequent death, and it would seem that these disorders may interact synergistically to affect mortality. Future research on mental disorders and health outcomes, as well as future clinical interventions, should pay more attention to comorbidity. GAD = generalized anxiety disorder; MDD = major depressive disorder; PTSD = posttraumatic stress disorder; HR = hazard ratio; CVD = cardiovascular disease; SBP = systolic blood pressure; DBP = diastolic blood pressure; BMI = body mass index; IQ = intelligence quotient.

Locus of control at age 10 years and health outcomes and behaviors at age 30 years: the 1970 British Cohort Study.

Objective: To examine the relationship between locus of control at age 10 years and self-reported health outcomes (overweight, obesity, psychological distress, health, and hypertension) and health behaviors (smoking and physical activity) at age 30, controlling for sex, childhood IQ, educational attainment, earnings, and socioeconomic position. Methods: Participants were members of the 1970 British Cohort Study, a national birth cohort. At age 10, 11,563 children took tests to measure locus of control and IQ. At age 30, 7551 men and women (65%) were interviewed about their health and completed a questionnaire about psychiatric morbidity. Results: Men and women with a more internal locus of control score in childhood had a reduced risk of obesity (odds ratio, 95% CI, for a SD increase in locus of control, 0.86, 0.78–0.95), overweight (0.87, 0.82–0.93), fair or poor self-rated health (0.89, 0.81–0.97), and psychological distress (0.86, 0.76–0.95). Women with a more internal locus of control had a reduced risk of high blood pressure (0.84, 0.76–0.92). Associations between childhood IQ and risk of obesity and overweight were weakened by adjustment for internal locus of control. Conclusion: Having a stronger sense of control over one’s own life in childhood seems to be a protective factor for some aspects of health in adult life. Sense of control provides predictive power beyond contemporaneously assessed IQ and may partially mediate the association between higher IQ in childhood and later risk of obesity and overweight. BMI= body mass index; SD= standard deviation

Physical fitness and lifetime cognitive change.

Objective: To test the hypothesis that physical fitness is associated with more successful cognitive aging. Methods: Surviving participants (N = 460) of the Scottish Mental Survey of 1932 were tested on the same general cognitive test at age 11 and 79 years. Measures of grip strength, 6-meter walk time, and lung function (forced expiratory volume from the lungs in 1 second [FEV1]) were assessed at age 79 years. Results: A latent physical fitness trait, derived by principal components analysis of the three fitness measures, was significantly associated with successful cognitive aging. Cognitive score at age 11, sex, social class, and APOE-ε4 genotype were included as covariables. Higher childhood IQ was associated with better lung function in old age. Conclusions: Physical fitness is associated with cognitive reserve. Intervention studies aimed at making older people fitter are good candidates to improve cognitive aging.

Intelligence in early adulthood and subsequent hospitalization for mental disorders

Background: Lower intelligence is a risk factor for several specific mental disorders. It is unclear whether it is a risk factor for all mental disorders, and whether it might be associated with illness severity. We examined the relation of premorbid intelligence with risk of hospital admission and with total admission rates, for the whole range of mental disorders. Methods: Participants were 1,049,663 Swedish men who took tests of intelligence on conscription into military service and were followed up with regard to hospital admissions for mental disorder, for a mean of 22.6 years. International Classification of Diseases diagnoses were recorded at discharge from the hospital. Results: Risk of hospital admission for all categories of mental disorder rose with each point decrease in the 9-point IQ score. For a standard deviation decrease in IQ, age-adjusted hazard ratios (95% confidence interval) were 1.60 for schizophrenia (1.55–1.65), 1.49 for other nonaffective psychoses (1.45–1.53), 1.50 for mood disorders (1.47–1.51), 1.51 for neurotic disorders (1.48–1.54), 1.60 for adjustment disorders (1.56–1.64), 1.75 for personality disorders (1.70–1.80), 1.75 for alcohol-related (1.73–1.77), and 1.85 for other substance-use disorders (1.82–1.88). Lower intelligence was also associated with greater comorbidity. Associations changed little on adjustment for potential confounders. Men with lower intelligence had higher total admission rates for mental disorders, a possible marker of clinical severity. Conclusions: Lower intelligence is a risk factor for the whole range of mental disorders and for illness severity.

Accelerated Telomere Attrition Is Associated with Relative Household Income, Diet and Inflammation in the pSoBid Cohort

Background It has previously been hypothesized that lower socio-economic status can accelerate biological ageing, and predispose to early onset of disease. This study investigated the association of socio-economic and lifestyle factors, as well as traditional and novel risk factors, with biological-ageing, as measured by telomere length, in a Glasgow based cohort that included individuals with extreme socio-economic differences. Methods A total of 382 blood samples from the pSoBid study were available for telomere analysis. For each participant, data was available for socio-economic status factors, biochemical parameters and dietary intake. Statistical analyses were undertaken to investigate the association between telomere lengths and these aforementioned parameters. Results The rate of age-related telomere attrition was significantly associated with low relative income, housing tenure and poor diet. Notably, telomere length was positively associated with LDL and total cholesterol levels, but inversely correlated to circulating IL-6. Conclusions These data suggest lower socio-economic status and poor diet are relevant to accelerated biological ageing. They also suggest potential associations between elevated circulating IL-6, a measure known to predict cardiovascular disease and diabetes with biological ageing. These observations require further study to tease out potential mechanistic links.