Cognitive performance in childhood and early adult illness: a prospective cohort study

The shared genetic architecture of smoking behaviours and psychiatric disorders: evidence from a population-based longitudinal study in England

BACKGROUND

Considering the co-morbidity of major psychiatric disorders and intelligence with smoking, to increase our understanding of why some people take up smoking or continue to smoke, while others stop smoking without progressing to nicotine dependence, we investigated the genetic propensities to psychiatric disorders and intelligence as determinants of smoking initiation, heaviness of smoking and smoking cessation in older adults from the general population.

RESULTS

Having utilised data from the English Longitudinal Study of Ageing (ELSA), our results showed that one standard deviation increase in MDD-PGS was associated with increased odds of being a moderate-heavy smoker (odds ratio [OR] = 1.11, SE = 0.04, 95%CI = 1.00-1.24, p = 0.028). There were no other significant associations between SZ-PGS, BD-PGS, or IQ-PGS and smoking initiation, heaviness of smoking and smoking cessation in older adults from the general population in the UK.

CONCLUSIONS

Smoking is a behaviour that does not appear to share common genetic ground with schizophrenia, bipolar disorders, and intelligence in older adults, which may suggest that it is more likely to be modifiable by smoking cessation interventions. Once started to smoke, older adults with a higher polygenic predisposition to major depressive disorders are more likely to be moderate to heavy smokers, implying that these adults may require targeted smoking cessation services.

High IQ in Early Adulthood Is Associated with Parkinson's Disease

Background:

High education level and high occupational complexity have been implicated as risk factors for Parkinson’s disease (PD).

Objective:

The objective was to determine whether cognitive capacity, measured as IQ, in early adulthood is associated with the subsequent development of PD.

Method:

Data on IQ were retrieved from the Swedish Military Service Conscription Registry, comprising Swedish males who enlisted for military service in the period 1968–1993 (N = 1,319,235). After exclusion, 1,189,134 subjects in total were included in the present study. Individuals who later developed PD (N = 1,724) were identified using the Swedish National Patient Register and the Swedish Cause of Death Register.

Results:

High education level was associated with PD. High IQ was associated with PD (p < 0.0001), both when analyzed as a continuous variable and when divided into three categories. The hazard ratio for the high IQ category compared to the low IQ category was 1.35 (95% confidence interval 1.17–1.55). Strong test results on the subtests, measuring verbal, logic, visuospatial and technical abilities, were also associated with PD. In a subgroup, smoking was inversely associated with PD, as well as with IQ.

Conclusions:

This study identifies high IQ to be a risk factor for PD.

Association between intelligence and coronary heart disease mortality: a population-based cohort study of 682 361 Swedish men

Background

Socio-economic position and intelligence predict coronary heart disease but their mutual associations are not yet well understood. We investigated associations between intelligence and coronary heart disease mortality and explored if they are confounded or modified by socio-economic position.

Design

This was a cohort-based follow-up study.

Methods

Data on intelligence, systolic and diastolic blood pressures and body mass index were measured at conscription examination at age 18 years in 682 361 Swedish men born 1951-1965. Data on parental and own education and social position were derived from censuses in 1960, 1970, 1980 and 1990. Follow-up data up to end of 2001 were derived from the Swedish Cause of Death Register and 737 coronary heart disease deaths were observed. Data were analyzed by Cox regression and conditional logistic regression models.

Results

An inverse association was found between intelligence and coronary heart disease mortality after adjustment for parental and own education and social position, body mass index and blood pressure (hazard ratio 0.92; 95% confidence interval 0.88-0.96). These associations were of similar strengths within all socio-economic categories and also found within 215 brother pairs discordant for coronary heart disease mortality and intelligence (odds ratio 0.76; 95% confidence interval 0.58-1.00).

Conclusions

Intelligence is associated with coronary heart disease mortality independently of socio-economic position. Health education messages should be tailored according to intellectual performance of the recipients, but also other factors are important for socio-economic coronary heart disease inequalities.

Impact of helminth infection during pregnancy on cognitive and motor functions of one-year-old children

OBJECTIVE

To determine the effect of helminth infection during pregnancy on the cognitive and motor functions of one-year-old children.

METHODS

Six hundred and thirty five singletons born to pregnant women enrolled before 29 weeks of gestation in a trial comparing two intermittent preventive treatments for malaria were assessed for cognitive and motor functions using the Mullen Scales of Early Learning, in the TOVI study, at twelve months of age in the district of Allada in Benin. Stool samples of pregnant women were collected at recruitment, second antenatal care (ANC) visit (at least one month after recruitment) and just before delivery, and were tested for helminths using the Kato-Katz technique. All pregnant women were administered a total of 600 mg of mebendazole (100 mg two times daily for 3 days) to be taken after the first ANC visit. The intake was not directly observed.

RESULTS

Prevalence of helminth infection was 11.5%, 7.5% and 3.0% at first ANC visit, second ANC visit and at delivery, respectively. Children of mothers who were infected with hookworms at the first ANC visit had 4.9 (95% CI: 1.3-8.6) lower mean gross motor scores compared to those whose mothers were not infected with hookworms at the first ANC visit, in the adjusted model. Helminth infection at least once during pregnancy was associated with infant cognitive and gross motor functions after adjusting for maternal education, gravidity, child sex, family possessions, and quality of the home stimulation.

CONCLUSION

Helminth infection during pregnancy is associated with poor cognitive and gross motor outcomes in infants. Measures to prevent helminth infection during pregnancy should be reinforced.

IQ and level of alcohol consumption—findings from a national survey of Swedish conscripts

BACKGROUND

Studies of the association between IQ and alcohol consumption have shown conflicting results. The aim of this study was to investigate the association between IQ test results and alcohol consumption, measured as both total alcohol intake and pattern of alcohol use.

METHODS

The study population consists of 49,321 Swedish males born 1949 to 1951 who were conscripted for Swedish military service 1969 to 1970. IQ test results were available from tests performed at conscription. Questionnaires performed at conscription provided data on total alcohol intake (consumed grams of alcohol/wk) and pattern of drinking. Multinomial and binomial logistic regressions were performed on the cross-sectional data to estimate odds ratios (ORs) with 95% confidence intervals (CIs). Adjustments were made for socioeconomic position as a child, psychiatric symptoms and emotional stability, and father's alcohol habits.

RESULTS

We found an increased OR of 1.20 (1.17 to 1.23) for every step decrease on the stanine scale to be a high consumer versus a light consumer of alcohol. For binge drinking, an increased OR of 1.09 (95% CI = 1.08 to 1.11) was estimated for every step decrease on the stanine scale. Adjustment for confounders attenuated the associations. Also, IQ in adolescence was found to be inversely associated with moderate/high alcohol consumption measured in middle age.

CONCLUSIONS

We found that lower results on IQ tests are associated with higher consumption of alcohol measured in terms of both total alcohol intake and binge drinking in Swedish adolescent men.

Comparing early years and childhood experiences and outcomes in Scotland, England and three city-regions: a plausible explanation for Scottish 'excess' mortality?

BACKGROUND

Negative early years and childhood experiences (EYCE), including socio-economic circumstances, parental health and parenting style, are associated with poor health outcomes both in childhood and adulthood. It has also been proposed that EYCE were historically worse in Scottish areas, especially Glasgow and the Clyde Valley, compared to elsewhere in the UK and that this variation can provide a partial explanation for the excess of ill health and mortality observed among those Scottish populations.

METHODS

Multiple logistic regression analysis was applied to two large, representative, British birth cohorts (the NCDS58 and the BCS70), to test the independent association of area of residence at ages 7 and 5 with risk of behavioural problems, respiratory problems and reading/vocabulary problems at the same age. Cohort members resident in Scotland were compared with those who were resident in England, while those resident in Glasgow and the Clyde Valley were compared with those resident in Merseyside and Greater Manchester.

RESULTS

After adjustment for a range of relevant variables, the risk of adverse childhood outcomes was found to be either no different, or lower, in the Scottish areas. At a national level, the study reinforces the combined association of socio-economic circumstances, parental health (especially maternal mental health) and parenting with child health outcomes.

CONCLUSION

Based on these samples, the study does not support the hypothesis that EYCE were worse in Scotland and Glasgow and the Clyde Valley. It seems, therefore (based on these data), less likely that the roots of the excess mortality observed in the Scottish areas can be explained by these factors.

Environmental tobacco smoke exposure and children's intelligence at 8-11 years of age

BACKGROUND

Evidence supporting a link between postnatal environmental tobacco smoke (ETS) exposure and cognitive problems among children is mounting, but inconsistent.

OBJECTIVES

We examined the relationship between ETS exposure, measured using urine cotinine, and IQ scores in Korean school-aged children.

METHODS

The participants were 996 children 8-11 years of age recruited from five administrative regions in South Korea. We performed a cross-sectional analysis of urinary cotinine concentrations and IQ scores obtained using the abbreviated form of a Korean version of the Wechsler Intelligence Scales for Children. Associations were adjusted for potential confounders, and estimates were derived with and without adjustment for mother's Full-Scale IQ (FSIQ) score.

RESULTS

After adjusting for sociodemographic and developmental covariates, urinary cotinine concentrations were inversely associated with FSIQ, Verbal IQ (VIQ), Performance IQ (PIQ), vocabulary, math, and block design scores. Following further adjustment for maternal IQ, only the VIQ scores remained significantly associated with urinary cotinine concentration (B = -0.31; 95% CI: -0.60, -0.03 for a 1-unit increase in natural log-transformed urine cotinine concentration; p = 0.03).

CONCLUSION

Urine cotinine concentrations were inversely associated with children's VIQ scores before and after adjusting for maternal IQ. Further prospective studies with serial measurements of cotinine are needed to confirm our findings.

Cumulative social risk exposure, infant birth weight, and cognitive delay in infancy

OBJECTIVE

To determine the effect of exposure to multiple social risks on cognitive delay at 9 months of age; and whether obstetric factors mediate the relationship between cumulative social risk and cognitive delay.

METHODS

Data were from 8950 mother-child dyads participating in the first wave of the Early Childhood Longitudinal Study, Birth Cohort. Cognitive delay was defined as falling in the lowest 10% of mental scale scores from the Bayley Short Form-Research Edition. Five social risk factors were combined and categorized into a social risk index. Staged multivariable logistic regressions were used to investigate whether obstetric factors mediated the impact of social risk on the odds of cognitive delay.

RESULTS

Infants with cognitive delay were more likely to live with social risks than infants without cognitive delay. The percentage of infants with cognitive delay increased with the number of social risks. In adjusted analyses, exposure to multiple social risk factors was associated with higher odds of cognitive delay at 9 months of age (adjusted odds ratio 2.11; 95% confidence interval 1.18-3.78 for 4 or more risks vs no risks). Accounting for birth weight attenuated this relationship (P < .001).

CONCLUSIONS

This population-based study investigated the independent and cumulative effects of social risk factors on cognitive delay in infancy. Findings revealed a significant cumulative relationship between exposure to social risk and cognitive delay, which was partly mediated by birth weight. Programs that address the social context of US infants are needed to improve their developmental trajectories.

Intelligence quotient in childhood and the risk of illegal drug use in middle-age: the 1958 National Child Development Survey

PURPOSE

High childhood IQ test scores have been associated with increased alcohol dependency and use in adult life, but the relationship between childhood IQ and illegal drug use in later life is unclear.

METHODS

Participants were 6713 members of the 1958 National Child Development Survey whose IQ was assessed at 11 years and had their lifetime illegal drug use measured at 42 years of age.

RESULTS

In analyses adjusted for a range of covariates, a 1 SD (15-point) increase in IQ scores was associated with an increased risk of illegal drug use in women: ever using cannabis (odds ratio [OR], 1.30; 95% confidence interval [95% CI], 1.16-1.45), cocaine (OR, 1.66; 95% CI, 1.21-2.27), amphetamines (OR, 1.50; 95% CI, 1.22-1.83), amyl nitrate (OR, 1.79; 95% CI, 1.30-2.46) and "magic mushrooms" (OR, 1.52; 95% CI, 1.18-1.98). Associations were of lower magnitude in men.

CONCLUSIONS

In this cohort, high childhood IQ was related to illegal drug use in adulthood.

Perinatal and socioeconomic risk factors for variable and persistent cognitive delay at 24 and 48 months of age in a national sample

The objective of this paper is to examine patterns of cognitive delay at 24 and 48 months and quantify the effects of perinatal and sociodemographic risk factors on persistent and variable cognitive delay. Using data from 7,200 children in the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B), multiple logistic regression models identified significant predictors of low cognitive functioning at 24 and 48 months. Additional multiple logistic models predicting cognitive delay at 48 months were estimated separately for children with and without delay at 24 months. Of the nearly 1,000 children delayed at 24 months, 24.2% remained delayed by 48 months; 7.9% of the children not delayed at 24 months exhibited delay at 48 months. Low and very low birthweight increased cognitive delay risk at 24, but not 48 months. Low maternal education had a strongly increasing effect (OR = 2.3 at 24 months, OR = 13.7 at 48 months), as did low family income (OR = 1.4 at 24 months, OR = 7.0 at 48 months). Among children delayed at 24 months, low maternal education predicted delay even more strongly at 48 months (OR = 30.5). Low cognitive functioning is highly dynamic from 24 to 48 months. Although gestational factors including low birthweight increase children’s risk of cognitive delay at 24 months, low maternal education and family income are more prevalent in the pediatric population and are much stronger predictors of both persistent and emerging delay between ages 24 and 48 months.

Fetal growth and the lifetime risk of generalized anxiety disorder

BACKGROUND

Anxiety disorders are thought to have their origins in early childhood, though they have not yet been studied as a potential outcome of impaired fetal growth, which has been implicated in the developmental etiologies of many psychopathologies. This study investigated the association between indicators of fetal growth and the development of generalized anxiety disorder (GAD).

METHODS

Indicators of fetal growth, including birth weight (BW) and ponderal index (PI), were assessed among 682 offspring of participants in Providence, Rhode Island, site of the Collaborative Perinatal Project. Participants were interviewed as adults, and their lifetime histories of GAD were assessed using the Diagnostic Interview Schedule. We used Cox regression to estimate the association between fetal growth indicators and development of GAD.

RESULTS

The lifetime risk of GAD differed between infants in the highest category of BW, PI, and all others. Newborns with birth weights below 3.5 kg (hazard ratio, HR: 2.38; CI=1.25, 4.55), in the lowest four BW Z-score quintiles (HR=2.49; CI=1.14, 5.45) or a PI in the lowest four quintiles (HR=2.33; CI=1.04, 5.00) had higher lifetime risks of GAD.

CONCLUSION

In contrast to earlier studies on psychiatric outcomes in relation to fetal growth, there was no linear relationship between birth weight and GAD. Although these results generally support the hypothesis that a healthy nutritional fetal uptake, as indicated by BW and PI, is associated with better lifetime mental health, further work is needed to characterize the nature of the association between fetal growth and subsequent psychopathology.

Revisiting the association between maternal smoking during pregnancy and ADHD

OBJECTIVE

Studies examining the relationship between maternal smoking during pregnancy and the development of Attention Deficit Hyperactivity Disorder (ADHD) among offspring have yielded mixed results, with some studies suggesting a strong association and others finding no association. These studies have varied in quality of design and measures. The purpose of this study was to evaluate the association between maternal smoking during pregnancy and offspring ADHD, using detailed prospective smoking data and subsequent follow-up data from the Collaborative Perinatal Project (CPP).

METHOD

Maternal smoking status was collected throughout pregnancy during the original CPP study. Offspring were followed-up in early adulthood and questioned about ADHD symptoms and diagnosis. Logistic regression was used to model the association between maternal smoking during pregnancy and ADHD. Linear and logistic regression were used to examine clinical characteristics and remission rates associated with ADHD in relation to maternal smoking.

RESULTS

No association was found between maternal smoking during pregnancy and offspring ADHD. Further, no differences in age of onset, number of symptoms, or likelihood of remission were found among ADHD subjects with and without a history of maternal smoking during pregnancy.

CONCLUSIONS

These findings do not support the hypothesis that maternal smoking during pregnancy is causally related to ADHD. Ongoing research should continue to strive to identify those environmental or genetic factors that may enhance the impact of maternal smoking on ADHD or that may be associated more clearly with the development and potential prevention of ADHD.

Cognitive test scores in male adolescent cigarette smokers compared to non-smokers: a population-based study

BACKGROUND

Although previous studies indicate that people with lower intelligence quotient (IQ) scores are more likely to become cigarette smokers, IQ scores of siblings discordant for smoking and of adolescents who began smoking between ages 18-21 years have not been studied systematically.

METHODS

Each year a random sample of Israeli military recruits complete a smoking questionnaire. Cognitive functioning is assessed by the military using standardized tests equivalent to IQ.

RESULTS

Of 20 221 18-year-old males, 28.5% reported smoking at least one cigarette a day (smokers). An unadjusted comparison found that smokers scored 0.41 effect sizes (ES, P < 0.001) lower than non-smokers; adjusted analyses remained significant (adjusted ES = 0.27, P < 0.001). Adolescents smoking one to five, six to 10, 11-20 and 21+ cigarettes/day had cognitive test scores 0.14, 0.22, 0.33 and 0.5 adjusted ES poorer than those of non-smokers (P < 0.001). Adolescents who did not smoke by age 18, and then began to smoke between ages 18-21 had lower cognitive test scores compared to never-smokers (adjusted ES = 0.14, P < 0.001). An analysis of brothers discordant for smoking found that smoking brothers had lower cognitive scores than non-smoking brothers (adjusted ES = 0.27; P = 0.014).

CONCLUSION

Controlled analyses from this large population-based cohort of male adolescents indicate that IQ scores are lower in male adolescents who smoke compared to non-smokers and in brothers who smoke compared to their non-smoking brothers. The IQs of adolescents who began smoking between ages 18-21 are lower than those of non-smokers. Adolescents with poorer IQ scores might be targeted for programmes designed to prevent smoking.

Childhood cognition and risk factors for cardiovascular disease in midadulthood: the 1958 British Birth Cohort Study

OBJECTIVES

We sought to establish whether associations between childhood cognition and risk factors for cardiovascular disease in adulthood are explained by common causes, or adult social position or health behavior.

METHODS

We analyzed associations between cognition at age 11 and cardiovascular disease risk factors at age 45 in the 1958 British birth cohort (n=9377), with and without adjustment for covariates.

RESULTS

General ability was inversely associated with systolic and diastolic blood pressure, glycosylated hemoglobin, triglycerides (in women), body mass index, and waist circumference. Systolic blood pressure decreased by 0.47 mm Hg (95% confidence interval [CI]=-0.90, -0.05) for a 1-standard-deviation increase in ability. Separate adjustment for social class at birth, education level by adulthood, adult social class, and health behaviors reduced the associations respectively by 14% to 34%, 36% to 50%, 14% to 36%, and 24% to 73%. Full adjustment reduced associations between ability and risk factors at age 45 years by 43% to 92%, abolishing all associations.

CONCLUSIONS

Increments across the distribution of childhood cognition are associated with improvements in cardiovascular risk profile in midlife, with associations primarily mediated through adult health behavior and social destinations.

The association of early IQ and education with mortality: 65 year longitudinal study in Malmö, Sweden

OBJECTIVES

To establish whether differences in early IQ explain why people with longer education live longer, or whether differences in father's or own educational attainment explain why people with higher early IQ live longer.

DESIGN

Population based longitudinal study. Mortality risks were estimated with Cox proportional hazards regressions.

SETTING

Malmö, Sweden.

PARTICIPANTS

1530 children who took IQ tests at age 10 and were followed up until age 75.

RESULTS

Own educational attainment was negatively associated with all cause mortality in both sexes, even when early IQ and father's education were adjusted for (hazard ratio (HR) for each additional year in school 0.91 (95% CI 0.85 to 0.97) for men and HR 0.88 (95 % CI 0.78 to 0.98) for women). Higher early IQ was linked with a reduced mortality risk in men, even when own educational attainment and father's education were adjusted for (HR for one standard deviation increase in IQ 0.85 (95 % CI 0.75 to 0.96)). In contrast, there was no crude effect of early IQ for women, and women with above average IQ had an increased mortality risk when own educational attainment was adjusted for, but only after the age of 60 (HR 1.60 (95 % CI 1.06 to 2.42)). Adding measures of social career over and above educational attainment to the model (for example, occupational status at age 36 and number of children) only marginally affected the hazard ratio for women with above average IQ (<5%).

CONCLUSIONS

Mortality differences by own educational attainment were not explained by early IQ. Childhood IQ was independently linked, albeit differently, to male adult mortality and to female adult mortality even when father's education and own educational attainment was adjusted for, thus social background and own social career seem unlikely to be responsible for mortality differences by childhood IQ. The clear difference in the effect of IQ between men and women suggests that the link between IQ and mortality involves the social and physical environment rather than simply being a marker of a healthy body to begin with. Cognitive skills should, therefore, be addressed in our efforts to create childhood environments that promote health.

The association between IQ in adolescence and a range of health outcomes at 40 in the 1979 US National Longitudinal Study of Youth

A link between pre-morbid intelligence and all cause mortality is becoming well established, but the aetiology of the association is not understood. Less is known about links with cause specific mortality and with morbidity. The aim of this study is to examine the association between intelligence measured in adolescence and a broad range of health outcomes ascertained at 40 years of age. We use data on 7476 participants in the US National Longitudinal Survey of Youth 1979 who had their cognitive ability measured at baseline and completed the 'Health at 40' interview module between 1998 and 2004. The Health at 40 module includes assessments of general health and depression, nine medically diagnosed conditions, and 33 common health problems. Higher mental test scores were associated with lower depression scores, better general health, significantly lower odds of having five of the nine diagnosed conditions and 15 of the 33 health problems. A health disadvantage of higher cognitive ability was evident for only three of the 33 health problems.

Disparities in the prevalence of cognitive delay: how early do they appear?

Cognitively delayed children are at risk for poor mental and physical health throughout their lives. The economically disadvantaged and some race/ethnic groups are more likely to experience cognitive delay, but the age at which delays first emerge and the underlying mechanisms responsible for disparities are not well understood. The objective of this study was to determine when sociodemographic disparities in cognitive functioning emerge, and identify predictors of low cognitive functioning in early childhood. Data were from 7308 singleton and 1463 multiple births in the Early Childhood Longitudinal Study-Birth Cohort (ECLS-B), a nationally representative cohort of children born in the USA in 2001. Multiple logistic regression analyses examined associations between sociodemographic characteristics and low cognitive functioning at 9 and 24 months, and tested whether gestational and birth-related factors mediate these associations. Sociodemographic characteristics were statistically significant predictors of low cognitive functioning among singletons at 24 months, including the three lowest quintiles of socio-economic status [lowest quintile, odds ratio (OR) = 2.7, 95% confidence interval [CI][1.7, 4.1]], non-white race/ethnicity (African American OR = 1.8 [95% CI 1.3, 2.5], Hispanic OR = 2.3 [95% CI 1.6, 3.2]), and gender (male OR = 2.1, [95% CI 1.7, 2.5]). Gestational and birth characteristics associated with low cognitive function at 9 months included very low and moderately low birthweight (OR = 55.0 [95% CI 28.3, 107.9] and OR = 3.6 [95% CI 2.6, 5.1]), respectively, and very preterm and moderately preterm delivery (OR = 3.6 [95% CI 2.0, 6.7] and OR = 2.4 [95% CI 1.7, 3.5]), respectively, but they had weaker effects by 24 months (ORs for birthweight: 3.7 [95% CI 2.3, 5.9] and 1.8 [95% CI 1.4, 2.3]; ORs for preterm: 1.8 [95% CI 1.1, 2.9] and 0.9 [95% CI 0.7, 1.3]). Results for multiple births were similar. Sociodemographic disparities in poor cognitive functioning emerged by 24 months of age, but were not mediated by gestational or birth characteristics. Further investigation of processes whereby social disadvantage adversely affects development prior to 24 months is needed.

Intelligence in girls and their subsequent smoking behaviour as mothers: the 1958 National Child Development Study and the 1970 British Cohort Study

BACKGROUND

Exposure to tobacco smoke either in utero or postnatally can have substantial adverse effects on child health, yet many women continue to smoke during pregnancy and after the birth. How women's intelligence in childhood affects their smoking behaviour as mothers is unclear.

METHODS

The participants were from two British national birth cohorts: 3325 women aged 33 years from the 1958 National Child Development Study and 1971 women aged 34 years from the 1970 British Cohort Study. We used structural equation modelling to examine the direct and indirect effects of intelligence measured at age 10-11 years, parental and current social class, educational attainment and age at first birth on smoking during pregnancy and current smoking status.

RESULTS

Forty per cent of women in the 1958 cohort smoked during pregnancy, compared with 28% of those from the 1970 cohort. In both cohorts, women with lower IQ in childhood were more likely as adults to smoke during pregnancy and to be a smoker currently. Structural equation modelling showed that the effects of childhood IQ on smoking behaviour were indirect, as they were statistically mediated by educational attainment and age at first birth. There was some effect of educational attainment and age at first birth on smoking behaviour over and above the effect of intelligence.

CONCLUSION

Childhood intelligence influenced women's smoking behaviour as mothers primarily through its contributions to educational attainment and age at first birth.

How does IQ affect onset of smoking and cessation of smoking--linking the Swedish 1969 conscription cohort to the Swedish survey of living conditions

OBJECTIVE

To examine the association between intelligence quotient (IQ) measured at ages 18 to 20 and onset of smoking, and the association between IQ and smoking cessation.

METHODS

Data on IQ, smoking, mental health, and social background among 49,321 Swedish men born 1949 to 51, collected at conscription for military service in 1969, were used. The association between IQ and smoking cessation was investigated among those 694 members of the full cohort also interviewed in the Swedish Level of Living Conditions study 1981 to 2002.

RESULTS

Lower IQ measured at ages 18 to 20 was weakly associated with increased prevalence of smoking, independently of indicators of mental illness and social misbehavior measured in late adolescence. By contrast, smoking cessation later in life among those who smoked at ages 18 to 20 was not associated with IQ. Among smokers, lower IQ was significantly associated with a lower level of smoking after adjusting for other factors.

CONCLUSION

Low IQ was associated with an increased prevalence of smoking in adolescence. However, the main part of this association disappeared after adjustment for measures of mental health and social function in early life. IQ was not associated with likelihood of quitting smoking.

Birth weight and cognitive ability in childhood among siblings and nonsiblings

OBJECTIVES

The purpose of this work was to examine whether the positive association between birth weight and childhood cognitive ability is seen within siblings from the same family, as well as between nonsiblings, and to determine whether these associations vary with age.

METHODS

We compared the association of birth weight with cognitive ability measured at ages 5 to 6, 7 to 9, and 11 to 12 years among a total of 5402 children from different families with that among 2236 to 3083 sibships from the National Longitudinal Study of Youth 1979-Children.

RESULTS

In the whole cohort, there were positive associations between birth weight and cognitive ability at all ages, with the association increasing with age from a 0.81-point increase at ages 5 to 6 years to 1.30 and 1.44 points at ages 7 to 9 and 11 to 12 years, respectively, per 1 SD of gestational age- and gender-adjusted birth weight z score. With adjustment for covariates, there was marked attenuation of these associations. Mean differences were 0.28 points in children aged 5 to 6 years, 0.67 points in those aged 7 to 9 years, and 0.52 points in those aged 11 to 12 years after adjusting for child's gender, race or ethnicity, year of birth, and age at test; maternal age, height, parity, education, smoking during pregnancy, and cognitive ability; and household income. Our family-based analyses that separated within- and between-family effects found that the between-family associations were much stronger than the within-family associations. However, adjustment for potential confounders attenuated the between-family associations, and there was no evidence for a difference in association comparing the between- and within-family associations.

CONCLUSIONS

In these data, the positive association between birth weight and childhood cognitive ability at ages 5 to 12 years is explained largely by family characteristics rather than a specific intrauterine effect.

The resources that matter: fundamental social causes of health disparities and the challenge of intelligence

A robust and very persistent association between indicators of socioeconomic status (SES) and the onset of life-threatening disease is a prominent concern of medical sociology. The persistence of the association over time and its generality across very different places suggests that no fixed set of intervening risk and protective factors can account for the connection. Instead, fundamental-cause theory views SES-related resources of knowledge, money, power prestige, and beneficial social connections as flexible resources that allow people to avoid risks and adopt protective strategies no matter what the risk and protective factors are in a given place or time. Recently, however, intelligence has been proposed as an alternative flexible resource that could fully account for the association between SES and health and thereby find its place as the epidemiologists' "elusive fundamental cause" (Gottfredson 2004). We examine the direct effects of intelligence test scores and adult SES in two data sets containing measures of intelligence, SES, and health. In analyses of prospective data from both the Wisconsin Longitudinal Study and the Health and Retirement Survey, we find little evidence of a direct effect of intelligence on health once adult education and income are held constant. In contrast, the significant effects of education and income on health change very little when intelligence is controlled. Although data limitations do not allow a definitive resolution of the issue, this evidence is inconsistent with the claim that intelligence is the elusive fundamental cause of health disparities, and instead supports the idea that the flexible resources people actively use to gain a health advantage are the SES-related resources of knowledge, money, power, prestige, and beneficial social connections.

Mental ability across childhood in relation to risk factors for premature mortality in adult life: the 1970 British Cohort Study

OBJECTIVE

To examine the relation of scores on tests of mental ability across childhood with established risk factors for premature mortality at the age of 30 years.

METHODS

A prospective cohort study based on members of the British Cohort Study born in Great Britain in 1970 who had complete data on IQ scores at five (N = 8203) or 10 (N = 8171) years of age and risk factors at age 30 years.

RESULTS

In sex-adjusted analyses, higher IQ score at age 10 years was associated with a reduced prevalence of current smoking (OR(per 1 SD advantage in IQ) 0.84; 95% CI 0.80, 0.88), overweight (0.88; 0.84, 0.92), obesity (0.84; 0.79, 0.92), and hypertension (0.90; 0.83, 0.98), and an increased likelihood of having given up smoking by the age of 30 years (1.25; 1.18, 1.24). These gradients were attenuated after adjustment for markers of socioeconomic circumstances across the life course, particularly education. There was no apparent relationship between IQ and diabetes. Essentially the same pattern of association was evident when the predictive value of IQ scores at five years of age was examined.

CONCLUSIONS

The mental ability-risk factor gradients reported in the present study may offer some insights into the apparent link between low pre-adult mental ability and premature mortality.

Why do children from socioeconomically disadvantaged families suffer from poor health when they reach adulthood? A life-course study

The authors investigated what risk factors contribute to an excess risk of poor adult health among children who experience socioeconomic disadvantage. Data came from 1,037 children born in Dunedin, New Zealand, in 1972-1973, who were followed from birth to age 32 years (2004-2005). Childhood socioeconomic status (SES) was measured at multiple points between birth and age 15 years. Risk factors evaluated included a familial liability to poor health, childhood/adolescent health characteristics, low childhood intelligence quotient (IQ), exposure to childhood maltreatment, and adult SES. Adult health outcomes evaluated at age 32 years were major depressive disorder, anxiety disorders, tobacco dependence, alcohol or drug dependence, and clustering of cardiovascular disease risk factors. Results showed that low childhood SES was associated with an increased risk of substance dependence and poor physical health in adulthood (for tobacco dependence, sex-adjusted relative risk (RR) = 2.27, 95% confidence interval (CI): 1.41, 3.65; for alcohol or drug dependence, RR = 2.11, 95% CI: 1.16, 3.84; for cardiovascular risk factor status, RR = 2.55, 95% CI: 1.46, 4.46). Together, the risk factors studied here accounted for 55-67% of poor health outcomes among adults exposed to low SES as children. No single risk factor emerged as the prime explanation, suggesting that the processes mediating the link between childhood low SES and adult poor health are multifactorial.

Socioeconomic status and health: youth development and neomaterialist and psychosocial mechanisms

There is substantial debate in the field of epidemiology over the theoretical underpinnings of socioeconomic status (SES)-disease mechanisms in the developed world. In particular, it has been debated whether psychosocial mechanisms are important in understanding these relationships, compared with material influences. Within an interdisciplinary context, this review synthesizes the youth development and resilience literatures in examination of this hypothesis. This review provides evidence that both classes of mechanisms are critical to understanding and addressing SES-disease mechanisms over the lifecourse. Research findings demonstrating the effects of these classes of factors point to the complicated and dynamic nature of how SES may impact disease. In the epidemiologic literature, investigators predominantly consider the cumulative impact of biological insults over time. A developmental perspective, however, provides evidence of the importance of psychosocial influences early in life on socioeconomic and health trajectories over the lifecourse. Future epidemiologic research should consider cumulative and developmental influences of early adversity--both psychosocial and material--on later health. This perspective may be particularly relevant to appropriately evaluating the impact of selection and causation in research on SES and disease and will also hopefully provide clarity to this ongoing theoretical debate.

Socioeconomic position, maternal IQ, home environment, and cognitive development

OBJECTIVE

To assess whether socioeconomic position, maternal intelligence (IQ), and the home environment are inter-related to cognitive development in childhood.

STUDY DESIGN

Prospective cohort study (n = 723) with cognitive tests at ages 2, 4, 7, and 11 to 13 years.

RESULTS

There were statistically significant positive associations of father's occupational prestige, Home Observation for Measurement of Environment (HOME) score, and maternal IQ with cognitive performance in childhood. After adjustment for confounding factors, there was an increase in cognitive development by 0.8 to 2.0, 2.9 to 4.8, and 4.2 to 9.0 points for a 10-unit increment in father's occupational prestige, maternal IQ, and HOME score, respectively.

CONCLUSIONS

These results demonstrate that socioeconomic position, maternal IQ, and the home environment are independently and positively predictive of children's cognitive development. These findings provide additional rationale for implementing social policies that reduce socioeconomic inequalities.

Examining life-course influences on chronic disease: the importance of birth cohort studies from low- and middle- income countries. An overview

The objectives of this overview are to describe the past and potential contributions of birth cohorts to understanding chronic disease aetiology; advance a justification for the maintenance of birth cohorts from low- and middle-income countries (LMIC); provide an audit of birth cohorts from LMIC; and, finally, offer possible future directions for this sphere of research. While the contribution of birth cohorts from affluent societies to understanding disease aetiology has been considerable, we describe several reasons to anticipate why the results from such studies might not be directly applied to LMIC. More than any other developing country, Brazil has a tradition of establishing, maintaining and exploiting birth cohort studies. The clear need for a broader geographical representation may be precipitated by a greater collaboration worldwide in the sharing of ideas, fieldwork experience, and cross-country cohort data comparisons in order to carry out the best science in the most efficient manner. This requires the involvement of a central overseeing body--such as the World Health Organization--that has the respect of all countries and the capacity to develop strategic plans for 'global' life-course epidemiology while addressing such issues as data-sharing. For rapid progress to be made, however, there must be minimal bureaucratic entanglements.

To what extent does IQ 'explain' socio-economic variations in function?

Background

The aims of this study were to examine the extent to which higher intellectual abilities protect higher socio-economic groups from functional decline and to examine whether the contribution of intellectual abilities is independent of childhood deprivation and low birth weight and other socio-economic and developmental factors in early life.

Methods

The Maastricht Aging Study (MAAS) is a prospective cohort study based upon participants in a registration network of general practices in The Netherlands. Information was available on 1211 men and women, 24 – 81 years old, who were without cognitive impairment at baseline (1993 – 1995), who ever had a paid job, and who participated in the six-year follow-up. Main outcomes were longitudinal decline in important components of quality of life and successful aging, i.e., self-reported physical, affective, and cognitive functioning.

Results

Persons with a low occupational level at baseline showed more functional decline than persons with a high occupational level. Socio-economic and developmental factors from early life hardly contributed to the adult socio-economic differences in functional decline. Intellectual abilities, however, took into account more than one third of the association between adult socio-economic status and functional decline. The contribution of the intellectual abilities was independent of the early life factors.

Conclusion

Rather than developmental and socio-economic characteristics of early life, the findings substantiate the importance of intellectual abilities for functional decline and their contribution – as potential, but neglected confounders – to socio-economic differences in functioning, successful aging, and quality of life. The higher intellectual abilities in the higher socio-economic status groups may also underlie the higher prevalences of mastery, self-efficacy and efficient coping styles in these groups.

Cognitive epidemiology

This glossary provides a guide to some concepts, findings and issues of discussion in the new field of research in which intelligence test scores are associated with mortality and morbidity. Intelligence tests are devised and studied by differential psychologists. Some of the major concepts in differential psychology are explained, especially those regarding cognitive ability testing. Some aspects of IQ (intelligence) tests are described and some of the major tests are outlined. A short guide is given to the main statistical techniques used by differential psychologists in the study of human mental abilities. There is a discussion of common epidemiological concepts in the context of cognitive epidemiology.

The association between cognitive ability measured at ages 18-20 and coronary heart disease in middle age among men: a prospective study using the Swedish 1969 conscription cohort

An association between childhood cognitive ability measured with IQ-tests and coronary heart disease (CHD) incidence has been reported recently. It is not clear from those studies to what extent the increased relative risk associated with lower cognitive ability may be explained by CHD risk factors. This study aims to investigate the association between cognitive ability measured at age 18-20 and incidence of CHD, acute myocardial infarction (AMI), and stroke among middle aged men adjusting for risk factors for CHD over the life course. Data on cognitive ability, and other risk factors for CHD (height, parental cardiovascular diseases (CVD) mortality, blood pressure, smoking, risky use of alcohol, BMI), were collected from 49,321 men, born in 1949-51, at conscription for compulsory military training in 1969/70 in Sweden. Information on socioeconomic factors in childhood (socioeconomic position and crowded housing) and adulthood (education, socioeconomic position, and income), as well as information on mortality and morbidity, was collected through national registers. Cognitive ability showed an inverse and graded association with CHD incidence. Adjustment for indicators of poor childhood circumstances, behavioural factors measured in late adolescence, and adult social circumstances strongly attenuated the increased risks of CHD and AMI. The contribution from adult social circumstances, after adjustment from all other factors, was very small. After adjustment for all risk factors no significantly increased relative risk was seen for stroke incidence. After adjustment for risk factors over the life course, the risk of CHD and AMI associated with cognitive ability decreased substantially, and was of borderline significance. Given the results from this study it is unlikely that cognitive ability is a risk factor on its own for CHD, AMI and stroke among men below 54 years of age.

Childhood cognitive performance and risk of generalized anxiety disorder

BACKGROUND

Perception of control over one's environment, particularly when faced with an ambiguous situation, has been identified as a critical cognitive process involved in worry and generalized anxiety disorder (GAD). Similarly, it is thought that individuals with lower cognitive skills feel less in control, and do not cope as well as individuals with higher cognitive skills. This study tests the hypothesis that individuals with higher cognitive skills are less likely to develop a lifetime diagnosis of GAD, and considers onset in three developmental periods: childhood, adolescence and adulthood.

METHODS

Survival analysis and multivariate regression models were used to evaluate the relationship between cognitive performance at age seven, and DSM-IV diagnosis of GAD. Study participants were 689 individuals in their mid-30s, who had been followed since birth as part of the National Collaborative Perinatal Project in Providence, RI, USA.

RESULTS

A 15-point (1 SD) advantage in childhood cognitive performance was significantly associated with a 50% reduced risk of lifetime GAD and an 89 and 57% reduction in risk of GAD in childhood and adolescence, respectively, after adjusting for relevant covariates including socio-economic status and parent history of mental health problems. These results were not affected by behavioural inhibition or learning disabilities in childhood.

CONCLUSIONS

Childhood cognitive performance is associated with a diagnosis of GAD in childhood and adolescence. Further research on the association between childhood cognitive performance and GAD is warranted.

Childhood IQ in relation to risk factors for premature mortality in middle-aged persons: the Aberdeen Children of the 1950s study

OBJECTIVE

A series of studies have shown an association between high childhood IQ scores and reduced rates of total mortality in adulthood. Several mechanisms have been advanced to explain these relationships, including mediation via established risk factors. This study examines the association between childhood IQ and a range of established physiological and behavioural risk factors for premature mortality in adulthood.

DESIGN, SETTING AND PARTICIPANTS

In 1962, 12,150 children took part in a school-based survey when their IQ scores were extracted from educational records. When re-surveyed forty years later (n = 7183; 63.7% response), they self-reported information on risk factors for premature mortality (smoking, heavy alcohol consumption, obesity, height, hypertension and diabetes).

MAIN RESULTS

In sex-adjusted analyses based on an analytical sample of 5340 (2687 women), higher childhood IQ scores were associated with a decreased prevalence of ever having smoked regularly in adulthood (OR(per SD increase in IQ) (95% CI): 0.77 (0.73 to 0.81)), heavy alcohol consumption (0.89 (0.84 to 0.94)), obesity (0.78 (0.72 to 0.83)) and overweight (0.86 (0.81 to 0.91)). Higher IQ scores were similarly related to a reduced prevalence of short stature and higher rates of smoking cessation in smokers; effects that were stronger in women (p value for interaction: < or =0.04). Adjusting for indicators of early and, particularly, later-life socioeconomic circumstances led to heavy attenuation of these gradients with statistical significance at conventional levels lost in most analyses.

CONCLUSIONS

The IQ-risk factor gradients reported may offer some insights into the apparent link between high pre-adult IQ and reduced mortality rates.

IQ in childhood and vegetarianism in adulthood: 1970 British cohort study

OBJECTIVE

To examine the relation between IQ in childhood and vegetarianism in adulthood.

DESIGN

Prospective cohort study in which IQ was assessed by tests of mental ability at age 10 years and vegetarianism by self-report at age 30 years.

SETTING

Great Britain.

PARTICIPANTS

8170 men and women aged 30 years participating in the 1970 British cohort study, a national birth cohort.

MAIN OUTCOME MEASURES

Self-reported vegetarianism and type of diet followed.

RESULTS

366 (4.5%) participants said they were vegetarian, although 123 (33.6%) admitted eating fish or chicken. Vegetarians were more likely to be female, to be of higher social class (both in childhood and currently), and to have attained higher academic or vocational qualifications, although these socioeconomic advantages were not reflected in their income. Higher IQ at age 10 years was associated with an increased likelihood of being vegetarian at age 30 (odds ratio for one standard deviation increase in childhood IQ score 1.38, 95% confidence interval 1.24 to 1.53). IQ remained a statistically significant predictor of being vegetarian as an adult after adjustment for social class (both in childhood and currently), academic or vocational qualifications, and sex (1.20, 1.06 to 1.36). Exclusion of those who said they were vegetarian but ate fish or chicken had little effect on the strength of this association.

CONCLUSION

Higher scores for IQ in childhood are associated with an increased likelihood of being a vegetarian as an adult.

Smoking in pregnancy in relation to gender and adult mortality risk in offspring: the Helsingborg Birth Cohort Study

BACKGROUND

Smoking in pregnancy is a well-documented risk factor for fetal growth impairment and poor perinatal outcomes. Less is known about the long-term effects of maternal smoking on offspring mortality.

METHODS

A follow-up study in national registers on total mortality and cancer based on a birth cohort from Helsingborg, Sweden, including data on 2,010 sons and 1,982 daughters born to mothers for whom the smoking habits during pregnancy (50% smokers) have been recorded.

RESULTS

A total of 92 offspring deaths were recorded (54 men, 38 women) during follow-up. Of these deaths, 43 deaths were related to trauma, 6 to circulatory disease, and 2 to endocrine disorders. In men, an elevated mortality risk was associated with increasing maternal smoking habits (p for trend 0.011), but in women with low birth weight (p for trend 0.006). A total of 47 incident offspring cancers were registered (18 in men and 29 in women). No significant relation was noted for maternal smoking habits and cancer in the offspring.

CONCLUSIONS

Maternal smoking during pregnancy is associated with an increased mortality risk in early adult life for male offspring but not for female offspring. This could represent the possible consequence of an increased susceptibility in male fetuses.

Childhood mental ability in relation to food intake and physical activity in adulthood: the 1970 British Cohort Study

OBJECTIVE

The purpose of this work was to examine the relation of scores on tests of mental ability in childhood with food consumption and physical activity in adulthood.

METHODS

Based on a cohort of >17,000 individuals born in Great Britain in 1970, 8282 had complete data for mental ability scores at 10 years of age and reported their food intake and physical activity patterns at 30 years of age.

RESULTS

Children with higher mental ability scores reported significantly more frequent consumption of fruit, vegetables (cooked and raw), wholemeal bread, poultry, fish, and foods fried in vegetable oil in adulthood. They were also more likely to have a lower intake of chips (French fries), nonwholemeal bread, and cakes and biscuits. There was some attenuation in these associations after adjustment for markers of socioeconomic position across the life course, which included educational attainment, with statistical significance lost in some analyses. Higher mental ability was positively associated with exercise habit, in particular, intense activity (defined by being out of breath/sweaty). The associations between mental ability and these behaviors were similar in both men and women, and they were somewhat stronger for verbal than nonverbal ability.

CONCLUSIONS

It is plausible that the skills captured by IQ tests, such as the ability to comprehend and reason, may be important in the successful management of a person's health behaviors.

Premorbid (early life) IQ and later mortality risk: systematic review

PURPOSE

Studies of middle-aged and particularly older-aged adults found that those with higher scores on tests of IQ (cognitive function) had lower rates of later mortality. Interpretation of such findings potentially is hampered by the problem of reverse causality: such somatic diseases as diabetes or hypertension, common in older adults, can decrease cognitive function. Studies that provide extended follow-up of the health experience of individuals who had their (premorbid) IQ assessed in childhood and/or early adulthood minimize this concern. The purpose of the present report is to systematically locate, evaluate, and interpret the findings of all such studies.

METHODS

We systematically identified individual-level studies linking premorbid IQ with later mortality by using four approaches: search of electronic databases (MEDLINE, EMBASE, and PSYCHINFO); scrutiny of the reference sections of identified reports; search of our own files; and contact with researchers in the field. Study quality was assessed by using predefined criteria.

RESULTS

Nine cohort studies met the inclusion criteria. Overall, study quality was moderate. All reports showed an inverse IQ-mortality relation; i.e., higher IQ scores were associated with decreased mortality risk. The nature of this relation (i.e., dose-response or threshold) and whether it differs by sex was unclear. The IQ-mortality association did not appear to be explained by reverse causality or selection bias. Confounding by other early-life factors also did not seem to explain the association, although some studies were not well characterized in this regard. Adult socioeconomic position appeared to mediate the IQ-mortality association in some studies, but this was not a universal finding.

CONCLUSIONS

In all studies, higher IQ in the first two decades of life was related to lower rates of total mortality in middle to late adulthood. Some plausible mechanistic pathways exist, but further examination is required. The precise nature of the IQ-mortality relation (particularly in ethnic minorities and women) and the link between IQ and disease-specific outcomes also warrants further research.

Childhood IQ and life course socioeconomic position in relation to alcohol induced hangovers in adulthood: the Aberdeen children of the 1950s study

OBJECTIVE

To examine the association between scores on IQ tests in childhood and alcohol induced hangovers in middle aged men and women.

DESIGN, SETTING, AND PARTICIPANTS

A cohort of 12 150 people born in Aberdeen (Scotland) who took part in a school based survey in 1962 when IQ test scores were extracted from educational records. Between 2000 and 2003, 7184 (64%) responded to questionnaire inquiries regarding drinking behaviour.

MAIN OUTCOME MEASURES

Self reported hangovers attributable to alcohol consumption on two or more occasions per month.

RESULTS

Higher IQ scores at 11 years of age were associated with a lower prevalence of hangovers in middle age (OR(per one SD advantage in IQ score); 95% CI: 0.80; 0.72, 0.89). This relation was little affected by adjustment for childhood indicators of socioeconomic position (0.82; 0.74, 0.91) but was considerably attenuated after control for adult variables (fully adjusted model: 0.89; 0.79, 1.01).

CONCLUSIONS

Higher childhood IQ was related to a lower prevalence of alcohol induced hangovers in middle aged men and women. The IQ-hangover effect may at least partially explain the link between early life IQ and adult mortality. This being the first study to examine this relation, more evidence is required.

Effect of maternal smoking during pregnancy on offspring's cognitive ability: empirical evidence for complete confounding in the US national longitudinal survey of youth

BACKGROUND

Numerous studies have reported that maternal cigarette smoking during pregnancy is related to lower IQ scores in the offspring. Confounding is a crucial issue in interpreting this association.

METHODS

In the US National Longitudinal Survey of Youth 1979, IQ was ascertained serially during childhood using the Peabody Individual Achievement Test, the total score for which comprises results on 3 subtests: mathematics, reading comprehension, and reading recognition. Maternal IQ was assessed by using the Armed Forces Qualification Test. There were 5578 offspring (born to 3145 mothers) with complete information for maternal smoking habits, total Peabody Individual Achievement Test score, and covariates.

RESULTS

The offspring of mothers who smoked > or = 1 pack of cigarettes per day during pregnancy had an IQ score (Peabody Individual Achievement Test total) that was, on average, 2.87 points lower than children born to nonsmoking mothers. Separate control for maternal education (0.27-IQ-point decrement) and, to a lesser degree, maternal IQ (1.51-IQ-point decrement) led to marked attenuation of the maternal-smoking-offspring-IQ relation. A similar pattern of results was seen when Peabody Individual Achievement Test subtest results were the outcomes of interest. The only exception was the Peabody Individual Achievement Test mathematics score, in which adjusting for maternal IQ essentially led to complete attenuation of the maternal-smoking-offspring-IQ gradient (0.66-IQ-point decrement). The impact of controlling for physical, behavioral, and other social indices was much less pronounced than for maternal education or IQ.

CONCLUSIONS

These findings suggest that previous studies that did not adjust for maternal education and/or IQ may have overestimated the association of maternal smoking with offspring cognitive ability.

Childhood IQ and deaths up to middle age: The Newcastle Thousand Families Study

OBJECTIVES

To test the hypothesis that an association exists between childhood IQ (at age 11) and mortality up to middle age.

STUDY DESIGN

The Newcastle Thousand Families study, a prospectively followed cohort, originally consisted of all 1142 births in the city of Newcastle in May and June 1947. Using data on 717 members of this cohort, we investigated the associations between the results of tests of IQ and English and arithmetic ability at age 11 years and mortality up to the end of 2003 using Cox's proportional hazards models.

RESULTS

Childhood IQ was significantly related to mortality in men (hazard ratio 0.57 for a standard deviation change in IQ at age 11; 95% CI 0.37, 0.86; P=0.007), but not in women (hazard ratio 0.79; 95% CI 0.49, 1.27; P=0.33). Adjustment for social class at birth had little effect on the associations. Similar results were seen when using the English and arithmetic scores.

CONCLUSIONS

These results confirm a recently reported association between individual differences in childhood cognition and mortality up to middle age, independent of childhood socio-economic circumstances. It is possible that the link between IQ and mortality is in part mediated through later life choices. Further research is required to identify the mechanisms by which such an association may occur, and to provide input to health promotion and disease management strategies that may improve health throughout life.

Childhood IQ in relation to obesity and weight gain in adult life: the National Child Development (1958) Study

OBJECTIVE

To examine the relation of childhood intelligence (IQ) test results with obesity in middle age and weight gain across the life course.

METHODS

We analysed data from the National Child Development (1958) Study, a prospective cohort study of 17 414 births to parents residing in Great Britain in the late 1950s. Childhood IQ was measured at age 11 years and body mass index (BMI), an indicator of adiposity, was assessed at 16, 23, 33 and 42 years of age. Logistic regression (in which BMI was categorised into obese and non-obese) and structural equation growth curve models (in which BMI was retained as a continuous variable) were used to estimate the relation between childhood IQ and adult obesity, and childhood IQ and weight gain, respectively.

RESULTS

In unadjusted analyses, lower childhood IQ scores were associated with an increased prevalence of adult obesity at age 42 years. This relation was somewhat stronger in women (OR(per SD decrease in IQ score) [95% CI]: 1.38 [1.26, 1.50]) than men (1.26 [1.15, 1.38]). This association remains statistically significant after adjusting for childhood characteristics, including socio-economic factors, but was heavily attenuated following control for adult characteristics, particularly education (women: 1.11 [0.99, 1.25]; men: 1.10 [0.98, 1.23]). When weight gain between age 16 and 42 years was the outcome of interest, structural equation modelling revealed that education and dietary characteristics in adult life mediated the association with childhood IQ.

CONCLUSIONS

A lower IQ score in childhood is associated with obesity and weight gain in adulthood. In the present study, this relation appears to be largely mediated via educational attainment and the adoption of healthy diets in later life.

Childhood intelligence in relation to adult coronary heart disease and stroke risk: evidence from a Danish birth cohort study

While recent studies have reported an inverse relation between childhood intelligence test scores and all-cause mortality in later life, the link with disease-specific outcomes has been rarely examined. Furthermore, the potential confounding effect of birthweight and childhood social circumstances is unknown. We investigated the relation of childhood intelligence with coronary heart disease (CHD) and stroke risk in a cohort of 6910 men born in 1953 in the Copenhagen area of Denmark. Events were ascertained from 1978 to 2000 using a cause-of-death register and hospital discharge records. There were 150 CHD (19 fatal; 131 non-fatal) and 93 stroke (4 fatal; 89 non-fatal) events during follow-up into mid-life. Childhood intelligence was inversely related to CHD with the highest rate apparent in adults with low childhood test scores (HR(lowest vs. highest quartile), 2.70; 95% confidence interval: 1.60, 4.57; P(trend) = 0.0001). After adjustment for paternal social class and birthweight, this association was attenuated only marginally. There was little evidence of a IQ-stroke relationship. The cognitive characteristics captured by IQ testing in the present study, such as communication and problem solving ability, appear to be associated with risk of CHD. Health promotion specialists and clinical practitioners may wish to consider these skills in their interactions with the general public. Replication of these results using studies which hold data on intelligence and socio-economic position across the life course is required.

Childhood cognitive performance and risk of mortality: a prospective cohort study of gifted individuals

Recent research suggests that childhood cognitive performance is associated with various health outcomes, but the nature of the relation is not well understood. It is unclear whether the association occurs across the continuum of cognitive performance, and if it is independent of socioeconomic status. Prospective data from the Terman Life Cycle Study were used to evaluate the hypothesis of a monotonic relation between childhood intelligence quotient (IQ) and adult mortality and to determine whether there exists a threshold beyond which the protective effects of IQ are no longer evident. A total of 897 individuals of school age who scored 135 or higher on the Stanford-Binet IQ test were recruited in 1922. Cox proportional hazards regression was used to estimate survival over a 64-year period. A 15-point advantage in childhood IQ was significantly associated with a decreased risk of mortality (hazard ratio = 0.68, 95% confidence interval: 0.49, 0.93) for IQ scores up to 163; beyond that, the risk of death plateaued. Results were similar when the sample was limited to those participants whose fathers had nonmanual occupations. Childhood IQ, even at the upper end of the distribution, is a significant predictor of mortality, independent of childhood social position.

Could associations between breastfeeding and insulin-like growth factors underlie associations of breastfeeding with adult chronic disease? The Avon Longitudinal Study of Parents and Children

OBJECTIVE

The influence of infant feeding method (breast/formula) on growth factor levels could underlie associations of breastfeeding with childhood growth and risk factors for cardiovascular disease. We investigated associations of having been breastfed with serum IGF-I and IGFBP-3 in childhood.

METHODS

Prospective birth cohort study (subsample of the Avon Longitudinal Study of Parents and Children, UK) based on 871 children born in 1991/1992 who underwent clinical follow-up and blood tests at age 7-8 years. A total of 488 (56%) children had complete data.

RESULTS

In children with complete data, the age- and sex-standardized IGF-I levels of those who were partially or exclusively breastfed were 6.1 and 13.8 ng/ml higher, respectively, than those who were never breastfed (increase in IGF-I levels per category of breastfeeding exclusivity: 7.1 ng/ml; 95% CI: 0.3-13.9; P = 0.04). In models also controlling for birthweight, gestational age, mother's age, and socioeconomic and dietary factors, the breastfeeding-IGF-I association was attenuated (regression coefficient: 3.3 ng/ml; -4.2-10.7; P = 0.4); further adjustment for IGFBP-3 made little difference (regression coefficient: 4.1 ng/ml; -2.8-10.9; P = 0.2). There was little evidence for an association between breastfeeding and IGFBP-3 or the molar ratio IGF-I/IGFBP-3.

CONCLUSIONS

The positive association between breastfeeding and IGF-I could be due to residual confounding or to chance. Nevertheless, the magnitude of the fully adjusted effect estimate and the novelty of the association suggest that larger studies should now be conducted to confirm or refute the hypothesis that variations in IGF-I by infant feeding mode explain associations of breastfeeding with health in later life.