Stroke is predicted by low visuospatial in relation to other intellectual abilities and coronary heart disease by low general intelligence

Multilevel multiverse meta-analysis indicates lower IQ as a risk factor for physical and mental illness

Is lower intelligence in early life an overlooked risk factor for later physical and mental illness? Intelligence shapes decision-making, career paths, and other health-relevant factors. However, our understanding of its association with health remains limited because there is no quantitative synthesis of the literature. Here, we conducted a comprehensive systematic review and meta-analysis of associations between intelligence test scores and mental and physical health. We included studies reporting standardized intelligence test scores obtained in childhood, adolescence, or early adulthood (<21 years of age) and their association with later-life health outcomes. We excluded studies limited to clinical populations without healthy controls. Our three-level multiverse analyses of 49 studies (N > 2,900,000) showed a 15-point IQ disadvantage in early life was associated with a 22 percent higher risk of later mental and physical illness (logHR = 0.20, 95% CI [0.13, 0.26]). Lower IQ predicted disease risk across various conditions, including schizophrenia, depression, dementia, and diabetes. Notably, the association between IQ and future health diminished with improved healthcare quality and when education was statistically held constant. Nevertheless, a meaningful effect of intelligence remained after adjusting for these variables. Multiple methods for detecting dissemination bias indicated that risk of bias was low. While our summary effect estimates are precise, all included data were collected in highly developed nations. Further, samples were predominantly male, potentially limiting generalizability. We show that lower IQ scores in early life are linked to a higher risk of later physical and mental illness. Improving education and healthcare quality appears as potential measures to address the issue. This research received no specific funding.

Cognitive function in adolescence and the risk of early-onset stroke

BACKGROUND

Stroke is increasingly prevalent at younger ages but the risk factors are uncertain. We examined the association between adolescent cognitive function and early-onset stroke.

METHODS

This was a nationwide population-based cohort study of 1 741 345 Israeli adolescents (42% women) who underwent comprehensive cognitive function tests at age 16-20 years, before mandatory military service, during 1987-2012. Cognitive function (range: 1-9) was categorised as low (1-3, corresponding to IQ score below 89), medium (4-7, IQ score range: 89-118), or high (8-9, IQ score above 118). Participant data were linked to the Israeli National Stroke Registry. Cox proportional hazard models were used to estimate risks for the first occurrence of ischaemic stroke during 2014-2018.

RESULTS

During 8 689 329 person-years of follow-up, up to a maximum age of 50 years, 908 first stroke events occurred (767 ischaemic and 141 haemorrhagic). Compared with a reference group of people with high cognitive function, body mass index-adjusted and sociodemographic-adjusted HRs (95% CIs) for early-onset stroke were 1.78 (1.33-2.38) in medium and 2.68 (1.96-3.67) in low cognitive function groups. There was evidence of a dose-response relationship (P for trend <0.0001) such that one-unit of lower cognitive function z-score was associated with a 33% increased risk of stroke (1.33; 1.23-1.42). These associations were similar for ischaemic stroke but lower for haemorrhagic stroke; persisted in sensitivity analyses that accounted for diabetes status and hypertension; and were evident before age 40 years.

CONCLUSIONS

Alongside adolescent obesity and hypertension, lower cognitive function may be a risk factor for early-onset stroke.

Brain working memory network indices as landmarks of intelligence

Identifying the neural correlates of intelligence has long been a goal in neuroscience. Recently, the field of network neuroscience has attracted researchers' attention as a means for answering this question. In network neuroscience, the brain is considered as an integrated system whose systematic properties provide profound insights into health and behavioral outcomes. However, most network studies of intelligence have used univariate methods to investigate topological network measures, with their focus limited to a few measures. Furthermore, most studies have focused on resting state networks despite the fact that brain activation during working memory tasks has been linked to intelligence. Finally, the literature is still missing an investigation of the association between network assortativity and intelligence. To address these issues, here we employ a recently developed mixed-modeling framework for analyzing multi-task brain networks to elucidate the most critical working memory task network topological properties corresponding to individuals' intelligence differences. We used a data set of 379 subjects (22-35 y/o) from the Human Connectome Project (HCP). Each subject's data included composite intelligence scores, and fMRI during resting state and a 2-back working memory task. Following comprehensive quality control and preprocessing of the minimally preprocessed fMRI data, we extracted a set of the main topological network features, including global efficiency, degree, leverage centrality, modularity, and clustering coefficient. The estimated network features and subject's confounders were then incorporated into the multi-task mixed-modeling framework to investigate how brain network changes between working memory and resting state relate to intelligence score. Our results indicate that the general intelligence score (cognitive composite score) is associated with a change in the relationship between connection strength and multiple network topological properties, including global efficiency, leverage centrality, and degree difference during working memory as it is compared to resting state. More specifically, we observed a higher increase in the positive association between global efficiency and connection strength for the high intelligence group when they switch from resting state to working memory. The strong connections might form superhighways for a more efficient global flow of information through the brain network. Furthermore, we found an increase in the negative association between degree difference and leverage centrality with connection strength during working memory tasks for the high intelligence group. These indicate higher network resilience and assortativity along with higher circuit-specific information flow during working memory for those with a higher intelligence score. Although the exact neurobiological implications of our results are speculative at this point, our results provide evidence for the significant association of intelligence with hallmark properties of brain networks during working memory.

Cognitive ability in young adulthood predicts risk of early-onset dementia in Finnish men

Objective

To test if the Finnish Defence Forces Basic Intellectual Ability Test scores at 20.1 years predicted risk of organic dementia or Alzheimer disease (AD).

Methods

Dementia was defined as inpatient or outpatient diagnosis of organic dementia or AD risk derived from Hospital Discharge or Causes of Death Registers in 2,785 men from the Helsinki Birth Cohort Study, divided based on age at first diagnosis into early onset (<65 years) or late onset (≥65 years). The Finnish Defence Forces Basic Intellectual Ability Test comprises verbal, arithmetic, and visuospatial subtests and a total score (scores transformed into a mean of 100 and SD of 15). We used Cox proportional hazard models and adjusted for age at testing, childhood socioeconomic status, mother's age at delivery, parity, participant's birthweight, education, and stroke or coronary heart disease diagnosis.

Results

Lower cognitive ability total and verbal ability (hazard ratio [HR] per 1 SD disadvantage >1.69, 95% confidence interval [CI] 1.01–2.63) scores predicted higher early-onset any dementia risk across the statistical models; arithmetic and visuospatial ability scores were similarly associated with early-onset any dementia risk, but these associations weakened after covariate adjustments (HR per 1 SD disadvantage >1.57, 95% CI 0.96–2.57). All associations were rendered nonsignificant when we adjusted for participant's education. Cognitive ability did not predict late-onset dementia risk.

Conclusion

These findings reinforce previous suggestions that lower cognitive ability in early life is a risk factor for early-onset dementia.

Education, Socioeconomic Status, and Intelligence in Childhood and Stroke Risk in Later Life: A Meta-analysis

BACKGROUND

Stroke is the second most common cause of death, and a common cause of dependency and dementia. Adult vascular risk factors and socioeconomic status (SES) are associated with increased risk, but less is known about early life risk factors, such as education, childhood SES, or intelligence (IQ).

METHODS

We comprehensively searched Medline, PsycINFO, and EMBASE from inception to November 2015. We included all studies reporting data on >50 strokes examining childhood/premorbid IQ, SES, and education. Two reviewers independently screened full texts and extracted and cross-checked data, including available risk factor adjustments. We meta-analyzed stroke risk using hazard ratios (HR), odds ratios (OR), and mean differences (MD). We tested effects of study and participant characteristics in sensitivity analyses and meta-regression, and assessed heterogeneity and publication bias.

RESULTS

We identified 90 studies examining stroke risk and education (79), SES (10), or IQ (nine) including approximately 164,683 stroke and over 5 million stroke-free participants. Stroke risk increased with lower education (OR = 1.35, 95% CI = 1.24, 1.48), SES (OR = 1.28, 95% CI = 1.12, 1.46), and IQ (HR = 1.17, 95% CI = 1.00, 1.37) in studies reporting point estimates, with similar associations for MD. We found minimal publication bias. Between-study heterogeneity was partly explained by participant age and case ascertainment method.

CONCLUSIONS

Education, childhood SES, and intelligence have modest but important associations with lifetime stroke, and hence dementia, risks. Future studies distinguishing between the individual and combined effects of education, childhood SES and intelligence are needed to determine the independent contribution of each factor to stroke risk. See video abstract at, http://links.lww.com/EDE/B210.

Association between breastfeeding and better preserved cognitive ability in an elderly cohort of Finnish men

BACKGROUND

Being breastfed in infancy has been shown to benefit neurodevelopment. However, whether the benefits persist to old age remains unclear.

METHODS

We examined the associations between breastfeeding and its duration on cognitive ability in young adulthood and old age, and on aging-related cognitive change over five decades. In total, 931 men from the Helsinki Birth Cohort Study born in 1934-1944 in Finland took the Finnish Defence Forces Basic Intellectual Ability Test (total and verbal, arithmetic and visuospatial subtest scores) twice, at ages 20.2 and 67.9 years, and had data on breastfeeding (yes v. no) and its duration ('never breastfed', 'up to 3', '3 to 6' and '6 or more months'). Linear and mixed model regressions tested the associations.

RESULTS

At 20.2 years, breastfed men had higher cognitive ability total and visuospatial subtest scores [mean differences (MDs) ranged between 3.0-3.9, p values < 0.013], and its longer duration predicted higher cognitive ability total and arithmetic and visuospatial subtest scores (MDs ranged between 3.0 and 4.8, p values < 0.039). At 67.9 years, breastfed men had higher total cognitive ability and all subtest scores (MDs ranged between 2.6 and 3.4, p values < 0.044) and its longer duration predicted all cognitive ability scores (MDs ranged between 3.1 and 4.7, p values < 0.050). Verbal subtest scores decreased over five decades in men who were never breastfed or were breastfed for 3 months or less, and increased in those breastfed for longer than 3 months.

CONCLUSIONS

Neurodevelopmental advantages of breastfeeding and its longer duration persist into old age, and longer duration of breastfeeding may benefit aging-related change, particularly in verbal reasoning ability.

Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study

Objectives To examine the association between intelligence measured in childhood and leading causes of death in men and women over the life course.Design Prospective cohort study based on a whole population of participants born in Scotland in 1936 and linked to mortality data across 68 years of follow-up.Setting Scotland.Participants 33 536 men and 32 229 women who were participants in the Scottish Mental Survey of 1947 (SMS1947) and who could be linked to cause of death data up to December 2015.Main outcome measures Cause specific mortality, including from coronary heart disease, stroke, specific cancer types, respiratory disease, digestive disease, external causes, and dementia.Results Childhood intelligence was inversely associated with all major causes of death. The age and sex adjusted hazard ratios (and 95% confidence intervals) per 1 SD (about 15 points) advantage in intelligence test score were strongest for respiratory disease (0.72, 0.70 to 0.74), coronary heart disease (0.75, 0.73 to 0.77), and stroke (0.76, 0.73 to 0.79). Other notable associations (all P<0.001) were observed for deaths from injury (0.81, 0.75 to 0.86), smoking related cancers (0.82, 0.80 to 0.84), digestive disease (0.82, 0.79 to 0.86), and dementia (0.84, 0.78 to 0.90). Weak associations were apparent for suicide (0.87, 0.74 to 1.02) and deaths from cancer not related to smoking (0.96, 0.93 to 1.00), and their confidence intervals included unity. There was a suggestion that childhood intelligence was somewhat more strongly related to coronary heart disease, smoking related cancers, respiratory disease, and dementia in women than men (P value for interactions <0.001, 0.02, <0.001, and 0.02, respectively).Childhood intelligence was related to selected cancer presentations, including lung (0.75, 0.72 to 0.77), stomach (0.77, 0.69 to 0.85), bladder (0.81, 0.71 to 0.91), oesophageal (0.85, 0.78 to 0.94), liver (0.85, 0.74 to 0.97), colorectal (0.89, 0.83 to 0.95), and haematopoietic (0.91, 0.83 to 0.98). Sensitivity analyses on a representative subsample of the cohort observed only small attenuation of the estimated effect of intelligence (by 10-26%) after adjustment for potential confounders, including three indicators of childhood socioeconomic status. In a replication sample from Scotland, in a similar birth year cohort and follow-up period, smoking and adult socioeconomic status partially attenuated (by 16-58%) the association of intelligence with outcome rates.Conclusions In a whole national population year of birth cohort followed over the life course from age 11 to age 79, higher scores on a well validated childhood intelligence test were associated with lower risk of mortality ascribed to coronary heart disease and stroke, cancers related to smoking (particularly lung and stomach), respiratory diseases, digestive diseases, injury, and dementia.

Intelligence in youth and health at age 50

Background

The link between intelligence in youth and all-cause mortality in later-life is well established. To better understand this relationship, the current study examines the links between pre-morbid intelligence and a number of specific health outcomes at age 50 using the NLSY-1979 cohort.

Methods

Participants were the 5793 participants in the NLSY-79 who responded to questions about health outcomes at age 50. Sixteen health outcomes were examined: two were summary measures (physical health and functional limitation), 9 were diagnosed illness conditions, 4 were self-reported conditions, and one was a measure of general health status. Linear and logistic regressions were used, as appropriate, to examine the relationship between intelligence in youth and the health outcomes. Age, sex and both childhood and adult SES, and its sub-components – income, education, & occupational prestige – are all adjusted for separately.

Results & conclusion

Higher pre-morbid intelligence is linked with better physical health at age 50, and a lower risk for a number of chronic health conditions. For example, a 1 SD higher score in IQ was significantly associated with increased odds of having good, very good, or excellent health, with an odds ratio of 1.70 (C.I. 1.55–1.86). Thirteen of the illness outcomes were significantly and negatively associated with IQ in youth; the odds ratios ranged from 0.85 for diabetes/high blood sugar to 0.65 for stroke, per one standard deviation higher score in IQ. Adjustment for childhood SES led to little attenuation but adult SES partially mediated the relationship for a number of conditions. Mediation by adult SES was not consistently explained by any one of its components—income, education, and occupation status. The current findings contribute to our understanding of lower intelligence as a risk factor for poor health and how this may contribute to health inequalities.

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We examined links between intelligence in youth and health at age 50 in NLSY-1979.

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Higher intelligence in youth is linked with better physical health at age 50.

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Higher intelligence in youth is linked with lower risk for chronic illnesses.

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Adult but not childhood SES partially mediated the intelligence–health relationship.

Intelligence in childhood and atherosclerosis of the carotid and peripheral arteries in later life: the Lothian Birth Cohort 1936

OBJECTIVE

There is some evidence that people who score higher on tests of intelligence in childhood have lower carotid intima-media thickness and higher ankle brachial index in middle age. These findings need replicating in other, older populations. We investigated the prospective relationship between intelligence in childhood and atherosclerosis in the carotid and peripheral arteries at age 73 years.

METHODS

Participants were 713 members of the Lothian Birth Cohort 1936 whose intelligence was assessed at age 11 years. At age 73 years, carotid intima-media thickness and degree of stenosis were measured using ultrasound imaging; ankle-brachial index was measured using Doppler ultrasound.

RESULTS

There were no significant associations between intelligence at age 11 and measures of atherosclerosis at age 73. In age- and sex-adjusted analyses, for a standard deviation higher score in intelligence, intima-media thickness (x 10) was lower by 0.07 (-0.20, 0.06) mm and ankle brachial index (x 10) was lower by 0.09 (-0.24, 0.07); odds ratios for having carotid stenosis >25% or peripheral arterial disease were 0.98 (0.82, 1.16) and 1.05 (0.81, 1.36) respectively.

CONCLUSION

In this study of people aged 73 years, higher childhood intelligence was not associated with reduced risk of atherosclerosis in the carotid or peripheral arteries.

Cognitive test scores in young men and subsequent risk of type 2 diabetes, cardiovascular morbidity, and death

BACKGROUND

The association between cognitive scores in young adulthood and long-term cardiometabolic risks remains unclear.

METHODS

Using population-based registries, we followed 6502 military conscripts from their 22nd birthday until death, emigration, or 55 years of age. We calculated risks and hazard ratios (HRs) associating quartiles of cognitive scores (very high, high, moderate, and low) with type 2 diabetes, hypertension, myocardial infarction, stroke, venous thromboembolism, and death before age 55 years.

RESULTS

The 33-year risk of the combined outcome was inversely associated with cognitive scores (26% for low and 16% for very high scores). Compared with very high scores, the HR for the combined outcome was 1.20 (95% confidence interval = 1.02, 1.41) for high, 1.43 (1.22, 1.68) for moderate, and 1.67 (1.43, 1.95) for low scores. Similar HRs were observed for individual outcomes.

CONCLUSION

Low cognitive score in young adulthood was a strong predictor for type 2 diabetes, cardiovascular morbidity, and death before 55 years of age.