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

Physical activity during pregnancy and intelligence in sons; A cohort study

The purpose was to examine the association between exercise during pregnancy and intelligence score in offspring. We analyzed data from 4008 women from the Aarhus Birth Cohort, Aarhus University Hospital, Denmark, recruited during pregnancy from July 1989 to November 1991 and their sons who were registered at conscription at 17-20 years of age. The women gave information by self-administered questionnaires during the first trimester including leisure-time physical activity and weekly hours of sport. This information was linked to the sons' measures of intelligence by Børge Priens test scores from the Danish Conscription Registry. Only sons were included since very few women register at conscription in Denmark. The main outcome measure was the Børge Priens test score as a continuous variable and with a low score defined as <10% of the population score. Analyses were adjusted for maternal body mass index, years in school, and smoking. Sons of women with light and moderate to heavy leisure-time physical activity had lower risk of having a low intelligence score compared with sons of women with sedentary activity: adjusted odds ratio (aOR) 0.66 (95% CI 0.49;0.88) and 0.46 (95% CI 0.23;0.93), respectively. Furthermore, sons of women engaged in sports had lower risk of a low intelligence score: aOR 0.50 (95% CI 0.30; 0.83) for 1-2 h/wk and 0.62 (95% CI 0.35; 1.10) for ≥3 h/wk compared with no weekly sports activity. In conclusion, a higher level of physical activity during pregnancy was associated with a lower risk of low intelligence score in early adulthood in sons.

The Intellectual Disability Mortality Disadvantage: Diminishing With Age?

On average, adults with intellectual disability (ID) have higher mortality risk than their peers in the general population. However, the effect of age on this mortality disadvantage has received minimal attention. Using data from the 1986-2011 National Health Interview Survey-Linked Mortality Files (NHIS-LMF), discrete time hazard models were used to compare mortality risk for adults with and without ID by age and gender. Increased mortality risk was present for all adults with ID, but was most pronounced among younger age females. The mortality differential between those with and without ID diminished with increased age for both females and males. Findings support the argument that heterogeneity of frailty may explain differences in mortality risk between those with and without ID.

Reaction time and mortality from the major causes of death: the NHANES-III study

OBJECTIVE

Studies examining the relation of information processing speed, as measured by reaction time, with mortality are scarce. We explored these associations in a representative sample of the US population.

METHODS

Participants were 5,134 adults (2,342 men) aged 20-59 years from the Third National Health and Nutrition Examination Survey (NHANES III, 1988-94).

RESULTS

Adjusted for age, sex, and ethnic minority status, a 1 SD slower reaction time was associated with a raised risk of mortality from all-causes (HR = 1.25, 95% CI 1.12, 1.39) and cardiovascular disease (CVD) (HR = 1.36, 95% CI 1.17, 1.58). Having 1 SD more variable reaction time was also associated with greater risk of all-cause (HR = 1.36, 95% CI 1.19, 1.55) and CVD (HR = 1.50, 95% CI 1.33, 1.70) mortality. No associations were observed for cancer mortality. The magnitude of the relationships was comparable in size to established risk factors in this dataset, such as smoking.

INTERPRETATION

Alongside better-established risk factors, reaction time is associated with increased risk of premature death and cardiovascular disease. It is a candidate risk factor for all-cause and cause-specific mortality.

IQ in childhood and atherosclerosis in middle-age: 40 Year follow-up of the Newcastle Thousand Families Cohort Study

Objective

Carotid intima-media thickness (IMT) is a known precursor to coronary heart disease (CHD) and other relevant health outcomes such as stroke and cognitive impairment. In addition, higher childhood intelligence has been associated with lower risk of coronary heart disease events in later life, although the mechanisms of effect are unclear. We therefore examined the association between childhood intelligence and atherosclerosis using carotid IMT as a marker of the atherosclerotic process.

Approach

Participants were 412 members of the Newcastle Thousand Families Study, a prospective cohort study of all 1142 births in the city of Newcastle in May and June 1947, who took an IQ test and English and arithmetic tests at age 11 years. Study members participated in a medical examination and lifestyle assessment at age 49–51 years during which IMT was measured using ultrasound techniques.

Results

Individuals with higher childhood IQ score had a lower mean IMT in middle-age. A standard deviation higher score in childhood overall IQ was associated with a 0.053 mm (95% CI −0.102, −0.004) lower IMT in men and a 0.039 mm (95% CI −0.080, −0.002) lower IMT in women. Similar levels of association were found for the English and arithmetic tests. After adjustment for a range of covariates including education, the size of effect was undiminished in men but increased in women.

Conclusions

In the present study, higher childhood IQ scores were associated with a lower degree of atherosclerosis by middle-age.

Fetal alcohol exposure and IQ at age 8: evidence from a population-based birth-cohort study

Background

Observational studies have generated conflicting evidence on the effects of moderate maternal alcohol consumption during pregnancy on offspring cognition mainly reflecting problems of confounding. Among mothers who drink during pregnancy fetal alcohol exposure is influenced not only by mother’s intake but also by genetic variants carried by both the mother and the fetus. Associations between children’s cognitive function and both maternal and child genotype at these loci can shed light on the effects of maternal alcohol consumption on offspring cognitive development.

Methods

We used a large population based study of women recruited during pregnancy to determine whether genetic variants in alcohol metabolising genes in this cohort of women and their children were related to the child’s cognitive score (measured by the Weschler Intelligence Scale) at age 8.

Findings

We found that four genetic variants in alcohol metabolising genes in 4167 children were strongly related to lower IQ at age 8, as was a risk allele score based on these 4 variants. This effect was only seen amongst the offspring of mothers who were moderate drinkers (1–6 units alcohol per week during pregnancy (per allele effect estimates were −1.80 (95% CI = −2.63 to −0.97) p = 0.00002, with no effect among children whose mothers abstained during pregnancy (0.16 (95%CI = −1.05 to 1.36) p = 0.80), p-value for interaction  = 0.009). A further genetic variant associated with alcohol metabolism in mothers was associated with their child’s IQ, but again only among mothers who drank during pregnancy.

The influence of childhood IQ and education on social mobility in the Newcastle Thousand Families birth cohort

Background

It has been suggested that social, educational, cultural and physical factors in childhood and early adulthood may influence the chances and direction of social mobility, the movement of an individual between social classes over his/her life-course. This study examined the association of such factors with intra-generational and inter-generational social mobility within the Newcastle Thousand Families 1947 birth cohort.

Methods

Multivariable logistic regression was used to examine the potential association of sex, housing conditions at age 5 years, childhood IQ, achieved education level, adult height and adverse events in early childhood with upward and downward social mobility.

Results

Childhood IQ and achieved education level were significantly and independently associated with upward mobility between the ages of 5 and 49-51 years. Only education was significantly associated (positively) with upward social mobility between 5 and 25 years, and only childhood IQ (again positively) with upward social mobility between 25 and 49-51 years. Childhood IQ was significantly negatively associated with downward social mobility. Adult height, childhood housing conditions, adverse events in childhood and sex were not significant determinants of upward or downward social mobility in this cohort.

Conclusions

As upward social mobility has been associated with better health as well as more general benefits to society, supportive measures to improve childhood circumstances that could result in increased IQ and educational attainment may have long-term population health and wellbeing benefits.

Intelligence in youth and all-cause-mortality: systematic review with meta-analysis

BACKGROUND

A number of prospective cohort studies have examined the association between intelligence in childhood or youth and life expectancy in adulthood; however, the effect size of this association is yet to be quantified and previous reviews require updating.

METHODS

The systematic review included an electronic search of EMBASE, MEDLINE and PSYCHINFO databases. This yielded 16 unrelated studies that met inclusion criteria, comprising 22,453 deaths among 1,107,022 participants. Heterogeneity was assessed, and fixed effects models were applied to the aggregate data. Publication bias was evaluated, and sensitivity analyses were conducted.

RESULTS

A 1-standard deviation (SD) advantage in cognitive test scores was associated with a 24% (95% confidence interval 23-25) lower risk of death, during a 17- to 69-year follow-up. There was little evidence of publication bias (Egger's intercept = 0.10, P = 0.81), and the intelligence-mortality association was similar for men and women. Adjustment for childhood socio-economic status (SES) in the nine studies containing these data had almost no impact on this relationship, suggesting that this is not a confounder of the intelligence-mortality association. Controlling for adult SES in five studies and for education in six studies attenuated the intelligence-mortality hazard ratios by 34 and 54%, respectively.

CONCLUSIONS

Future investigations should address the extent to which attenuation of the intelligence-mortality link by adult SES indicators is due to mediation, over-adjustment and/or confounding. The explanation(s) for association between higher early-life intelligence and lower risk of adult mortality require further elucidation.

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.

Childhood socioeconomic status modifies the association between intellectual abilities at age 20 and mortality in later life

Background

People who score poorly in intellectual ability tests have shorter life expectancy. A study was undertaken to determine whether this association is different in people from different socioeconomic backgrounds.

Methods

The mortality of 2786 men born in Helsinki, Finland during 1934–1944 who, as military conscripts, underwent a standardised intellectual ability test comprising verbal, visuospatial and arithmetic reasoning subtests was studied. Mortality data came from the Finnish Death Register.

Results

Comparing men in the lowest and highest test score quartiles, HRs for all-cause mortality were 1.9 (95% CI 1.4 to 2.5) for verbal reasoning, 2.2 (95% CI 1.6 to 3.0) for visuospatial reasoning and 1.9 (95% CI 1.4 to 2.5) for arithmetic reasoning, corresponding to 2.6, 3.4 and 2.6 excess years of life lost, respectively. Associations were similar for cardiovascular and non-cardiovascular mortality. Intellectual ability scores were stronger predictors in men who grew up in middle-class families. Compared with middle-class men in the highest quartile of the visuospatial reasoning score, middle-class men in the lowest quartile lost 6.5 years of life while men from families of manual workers in the highest quartile lost 2.8 years and men in the lowest quartile lost 5.6 years.

Conclusions

High intellectual ability in men aged 20 protects them from mortality in later life. This effect is stronger in men who grew up in middle-class families than in those who grew up in manual worker families. This finding suggests that early life conditions that are unfavourable to the development of cognitive abilities negate the life expectancy benefits of being born into a more affluent family.

Low childhood IQ and early adult mortality: the role of explanatory factors in the 1958 British Birth Cohort

OBJECTIVE

To examine whether the association between childhood IQ and later mortality risk was explained by early developmental advantages or mediated by adult sociodemographic factors and health behaviors.

PARTICIPANTS AND METHODS

Participants were 10 620 men and women from the 1958 British Birth Cohort Study whose IQ was assessed at the age of 11 years and who were followed up to age 46. Childhood covariates included birth weight, childhood height at 11 years of age, problem behaviors, father's occupational class, parents' interest in child's education, family size, and family difficulties. Adult risk factors were assessed at ages 23, 33, and 42 years, and they included education, occupational class, marital status, smoking, BMI, alcohol use, and psychosomatic symptoms.

RESULTS

Between ages 23 and 46 years, 192 participants died. Higher childhood IQ was related to lower mortality risk (standardized odds ratio [OR]: 0.80 [95% confidence interval (CI): 0.69-0.93]) with no gender differences (OR: 0.81 [95% CI: 0.67-0.98] [men] and 0.79 [95% CI: 0.63-0.98] [women]). Adjusting for parents' interest in child's education attenuated the IQ-mortality association by 15% to 20%, and adult education and psychosomatic symptoms both attenuated the association by 25%. Other covariates were less influential.

CONCLUSIONS

In a cohort of British men and women, the most important explanatory factors for the lower mortality rate among individuals with high IQ were parental interest in child's education, high adult educational level, and low prevalence of psychosomatic symptoms. However, common sociodemographic risk factors and health behaviors may not be sufficient to explain the association between IQ and early mortality completely.

IQ, socioeconomic status, and early death: The US National Longitudinal Survey of Youth

OBJECTIVE

To assess whether the association between cognitive ability (IQ) and early mortality is mediated by socioeconomic status (SES) or whether the association between SES and mortality reflects a spurious association caused by IQ.

METHODS

The participants were from the US National Longitudinal Survey of Youth (n = 11,321). IQ was assessed at age 16 to 23 years and the participants were followed up to 40 to 47 years of age.

RESULTS

Controlling for sex, birth year, race/ethnicity, baseline health, and parental education, higher IQ was associated with lower probability of death (odds ratio (OR) per 1-standard deviation increase in IQ = 0.78, 95% confidence interval (CI) = 0.66, 0.91). This association disappeared (OR = 0.99, 95% CI = 0.81, 1.20) when adjusted for education and household income. Adjustment for IQ had no effect on the association between SES and mortality. These findings were similar in Hispanic, Black, and White/other participants and in women and men. Parental education moderated the IQ-mortality association so that this association was not observed in participants with low parental education.

CONCLUSIONS

Low IQ predicts early mortality in the US population and this association is largely explained by SES. The results do not support the alternative hypothesis that the socioeconomic gradient in early mortality would reflect IQ differences.

Predictors and correlates of edentulism in the healthy old people in Edinburgh (HOPE) study

OBJECTIVES

To determine the extent to which correlates of edentulism are explained by an association between tooth loss and cognitive ability.

METHODS

Participants in the Healthy Old People in Edinburgh (HOPE) study aged 70 or more at baseline were assessed and health, cognitive, socio-economic and socio-environmental data collected on four consecutive occasions. It was noted whether the participant had any retained teeth and if not, the age when the last tooth was lost. Prior determinants of edentulism were investigated with binary logistic regression models. At the 9-year follow-up, associations with edentulism were examined using general linear models with edentulism as an independent factor.

RESULTS

201 participants were adequately tested, of whom 104 (51.7%) were edentulous. A logistic regression model that considered age, sex, education, social class, deprivation index of residence, objective distance from dentist, participant's estimate of distance from dentist and NART-estimated IQ (NARTIQ) found age (p = 0.032), occupational class (p = 0.019) and NARTIQ (p = 0.027) as significant predictors of edentulism. Cox's proportional hazards modelling found only NARTIQ (p = 0.050) to be correlated. Being edentulous was associated with poorer respiratory function but not hand grip strength (p = 0.23). Edentulous participants had lower self esteem scores (p = 0.020) and poorer dietary assessment scores (p = 0.028). Being edentulous was also associated with significantly lower mean scores on all cognitive testing, although these associations became non-significant after adjustment for NARTIQ and age.

CONCLUSIONS

In healthy older people, edentulism is associated with relative impairment of cognitive ability, although this association is explained by the fact that lower original intelligence predisposes to edentulism and poorer performance on cognitive tests in old age. Once original intelligence is adjusted for, tooth loss is not related to cognitive ability. Tooth loss is, however, associated with poorer status across a wide range of health measures: physical health, nutrition, disability and self-esteem. Establishing the degree to which these health outcomes are causally related to edentulism could usefully be factored into cost-benefit analyses of programmes designed to prevent tooth loss.