Are the educational differences in incidence of cardiovascular disease explained by underlying familial factors? A twin study

Child health and its effect on adult social capital accumulation

Although studies have demonstrated important effects of poor health in childhood on stocks of human and health capital, little research has tested economic theories to investigate the effect of child health on social capital in adulthood. Studies on the influence of child health on adult social capital are mixed and have not used sibling fixed effects models to account for unmeasured family and genetic characteristics, that are likely to be important. Using the Add-Health sample, health in childhood was assessed as self-rated health, the occurrence of a physical health condition or mental health condition, while social capital in adulthood was measured as volunteering, religious service attendance, team sports participation, number of friends, social isolation, and social support. We used sibling fixed effects models, which attenuated several associations to non-significance. In sibling fixed effects models there was significant positive effects of greater self-rated health on participation in team sports and social support, and negative effect of mental health in childhood on social isolation in adulthood. These results suggest that children with poor health require additional supports to build and maintain their stock of social capital and highlight further potential benefits to efforts that address poor child health.

Socioeconomic inequalities in cardiovascular disease: a causal perspective

Socioeconomic inequalities in cardiovascular disease (CVD) persist in high-income countries despite marked overall declines in CVD-related morbidity and mortality. After decades of research, the field has struggled to unequivocally answer a crucial question: is the association between low socioeconomic position (SEP) and the development of CVD causal? We review relevant evidence from various study designs and disciplinary perspectives. Traditional observational, family-based and Mendelian randomization studies support the widely accepted view that low SEP causally influences CVD. However, results from quasi-experimental and experimental studies are both limited and equivocal. While more experimental and quasi-experimental studies are needed to aid causal understanding and inform policy, high-quality descriptive studies are also required to document inequalities, investigate their contextual dependence and consider SEP throughout the lifespan; no simple hierarchy of evidence exists for an exposure as complex as SEP. The COVID-19 pandemic illustrates the context-dependent nature of CVD inequalities, with the generation of potentially new causal pathways linking SEP and CVD. The linked goals of understanding the causal nature of SEP and CVD associations, their contextual dependence, and their remediation by policy interventions necessitate a detailed understanding of society, its change over time and the phenotypes of CVD. Interdisciplinary research is therefore key to advancing both causal understanding and policy translation.

Demystifying the link between higher education and liberal values: A within-sibship analysis of British individuals' attitudes from 1994-2020

The link between university graduation and liberal values is well-established and often taken as evidence that higher education participation causes attitudinal change. Identification of education's causal influence in shaping individual preferences is notoriously difficult as it necessitates isolating education's effect from self-selection mechanisms. This study exploits the household structure of the Harmonized British Household Panel Study and Understanding Society data to tighten the bounds of causal inference in this area and ultimately, to provide a more robust estimate of the independent effect of university graduation on political attitudes. Results demonstrate that leveraging sibling fixed-effects to control for family-invariant pre-adult experiences reduces the size of higher education's effect on cultural attitudes by at least 70%, compared to conventional methods. Significantly, within-sibship models show that obtaining higher education qualifications only has a small direct causal effect on British individuals' adult attitudes, and that this effect is not always liberalizing. This has important implications for our understanding of the relationship between higher education and political values. Contrary to popular assumptions about education's liberalizing role, this study demonstrates that the education-political values linkage is largely spurious. It materializes predominately because those experiencing pre-adult environments conducive to the formation of particular values disproportionately enroll at universities.

Educational attainment impacts drinking behaviors and risk for alcohol dependence: results from a two-sample Mendelian randomization study with ~780,000 participants

Observational studies suggest that lower educational attainment (EA) may be associated with risky alcohol use behaviors; however, these findings may be biased by confounding and reverse causality. We performed two-sample Mendelian randomization (MR) using summary statistics from recent genome-wide association studies (GWAS) with >780,000 participants to assess the causal effects of EA on alcohol use behaviors and alcohol dependence (AD). Fifty-three independent genome-wide significant SNPs previously associated with EA were tested for association with alcohol use behaviors. We show that while genetic instruments associated with increased EA are not associated with total amount of weekly drinks, they are associated with reduced frequency of binge drinking ≥6 drinks (ßIVW = -0.198, 95% CI, -0.297 to -0.099, PIVW = 9.14 × 10-5), reduced total drinks consumed per drinking day (ßIVW = -0.207, 95% CI, -0.293 to -0.120, PIVW = 2.87 × 10-6), as well as lower weekly distilled spirits intake (ßIVW = -0.148, 95% CI, -0.188 to -0.107, PIVW = 6.24 × 10-13). Conversely, genetic instruments for increased EA were associated with increased alcohol intake frequency (ßIVW = 0.331, 95% CI, 0.267-0.396, PIVW = 4.62 × 10-24), and increased weekly white wine (ßIVW = 0.199, 95% CI, 0.159-0.238, PIVW = 7.96 × 10-23) and red wine intake (ßIVW = 0.204, 95% CI, 0.161-0.248, PIVW = 6.67 × 10-20). Genetic instruments associated with increased EA reduced AD risk: an additional 3.61 years schooling reduced the risk by ~50% (ORIVW = 0.508, 95% CI, 0.315-0.819, PIVW = 5.52 × 10-3). Consistency of results across complementary MR methods accommodating different assumptions about genetic pleiotropy strengthened causal inference. Our findings suggest EA may have important effects on alcohol consumption patterns and may provide potential mechanisms explaining reported associations between EA and adverse health outcomes.

Health and criminal justice system involvement among African American siblings

IMPORTANCE

Health disparities between African Americans and Whites have persisted in the United States. Researchers have recently hypothesized that the relatively poor health of African Americans may be caused, in part, by African American overrepresentation in the criminal justice system.

OBJECTIVES

To test the hypothesis that criminal justice system involvement is associated with poor health and greater health risk when controlling for unobserved family factors through a discordant sibling design.

METHODS

Subjects were drawn from the Carolina African American Twin Study of Aging (CAATSA). Criminal conviction records were extracted from North Carolina's Department of Public Safety. Six measures of health and one measure of health risk were analyzed. The health of convicted respondents was compared to that of unrelated non-convicted respondents matched on childhood and demographic factors ("matched sample"). Convicted respondents were also compared to non-convicted siblings ("discordant sibling sample").

RESULTS

The matched sample included 134 CAATSA respondents. On average, convicted CAATSA respondents, compared to matched non-convicted respondents, were in worse health. Convicted respondents had worse mean self-reported health, worse lung function, more depressive symptoms, and smoked more. The discordant sibling sample included 74 respondents. Convicted siblings and non-convicted siblings had similar self-reported health, depressive symptoms, and smoking. In general, non-convicted siblings were in worse health than non-convicted respondents from the matched sample, implying that poor health runs in families.

CONCLUSIONS

This study provided preliminary evidence that some of the association between a criminal record and poor health is confounded by family factors. Though more research is needed to support these results, the study suggests that criminal involvement may not be associated with the surfeit of health problems observed among African Americans. The criminal justice system, nonetheless, could be used to decrease the health disparity.

Socioeconomic inequalities in the prevalence of biomarkers of cardio-metabolic disease in South Korea: Comparison of the Health Examinees Study to a nationally representative survey

BACKGROUND/OBJECTIVES

This study aimed to examine socioeconomic inequalities in the prevalence of biomarkers of cardiovascular disease and diabetes in the newly developed large-scale genomic cohort study of Korean adults, the Health Examinees-Gem (HEXA-G), with a comparison of the nationally representative cross-sectional study, the Korea National Health and Nutrition Examination Survey (K-NHANES).

SUBJECTS/METHODS

Using the HEXA-G and the K-NHANES from 2007-2012, we analyzed the age-adjusted relative risk (RR) and prevalence of enlarged waist circumference (EWC), elevated triglycerides (ET), low HDL cholesterol (LHC), elevated blood pressure (EBP) and elevated blood glucose (EBG) by income and educational groups for adults at age 40-69.

RESULTS

For men, the prevalence of risk factors was similar across different income and educational groups (p>0.1), and between the K-NHANES and the HEXA-G. Among five risk factors, EBG showed the greatest discrepancy by 7 to 11 percentage points (i.e., the prevalence of 0.43 and 0.36 for college graduates, respectively, in K-NHANES and HEXA-G). For women, socioeconomic inequalities appeared for the five risk factors. Prevalence of risk factors was mostly lower in the HEXA-G than the K-NHANES, by approximately 11.0 percentage points. Especially, the discrepancy between K-NHANES and HEXA-G was largest in EBG (i.e., the prevalence of 0.31 and 0.20 for the lowest income groups, respectively).

CONCLUSION

The HEXA-G shows broadly similar socioeconomic inequality in prevalence of cardio-metabolic risk factors to the nationally representative sample with more modest socioeconomic inequality among women in the HEXA-G than the K-NHANES.

The Relationship Between Education and Health: Reducing Disparities Through a Contextual Approach

Adults with higher educational attainment live healthier and longer lives compared with their less educated peers. The disparities are large and widening. We posit that understanding the educational and macrolevel contexts in which this association occurs is key to reducing health disparities and improving population health. In this article, we briefly review and critically assess the current state of research on the relationship between education and health in the United States. We then outline three directions for further research: We extend the conceptualization of education beyond attainment and demonstrate the centrality of the schooling process to health; we highlight the dual role of education as a driver of opportunity but also as a reproducer of inequality; and we explain the central role of specific historical sociopolitical contexts in which the education-health association is embedded. Findings from this research agenda can inform policies and effective interventions to reduce health disparities and improve health for all Americans.

Why does college education matter? Unveiling the contributions of selection factors

This study investigates the contributions of pre-college selection factors that may partially lead to the college degree - health link by using longitudinal data from the National Longitudinal Survey of Youth (1979) cohort. Propensity score matching method finds that the effects of college degree on various health outcomes (self-rated health, physical component summary index, health limitations, CESD scale) are reduced by 51% on average (range: 37%-70%) in the matched sample. Among these observed factors, cognitive skill is the biggest confounder, followed by pre-college health and socioeconomic characteristics (marital aspiration, years of schooling, marriage, fertility, poverty status) and non-cognitive skills (e.g., self-esteem). Rotter Internal-External Locus of Control scale is not significantly associated with all four health measures. The effects of most indicators of family background (parental education, family stability, family size, religious background) on the health of adult children are not direct but through offspring's early adulthood health and socioeconomic status.

The Effect of Schooling on Mortality: New Evidence From 50,000 Swedish Twins

By using historical data on about 50,000 twins born in Sweden during 1886-1958, we demonstrate a positive and statistically significant relationship between years of schooling and longevity. This relation remains almost unchanged when exploiting a twin fixed-effects design to control for the influence of genetics and shared family background. This result is robust to controlling for within-twin-pair differences in early-life health and cognitive ability, as proxied by birth weight and height, as well as to restricting the sample to MZ twins. The relationship is fairly constant over time but becomes weaker with age. Literally, our results suggest that compared with low levels of schooling (less than 10 years), high levels of schooling (at least 13 years of schooling) are associated with about three years longer life expectancy at age 60 for the considered birth cohorts. The real societal value of schooling may hence extend beyond pure labor market and economic growth returns. From a policy perspective, schooling may therefore be a vehicle for improving longevity and health, as well as equality along these dimensions.

Educational inequality in cardiovascular diseases: a sibling approach

AIMS

Educational inequality in diseases in the circulatory system (here termed cardiovascular disease) is well documented but may be confounded by early life factors. The aim of this observational study was to examine whether the associations between education and all cardiovascular diseases, ischaemic heart disease and stroke, respectively, were explained by family factors shared by siblings.

METHODS

The study population included all individuals born in Denmark between 1950 and 1979 who had at least one full sibling born in the same period. Using Cox regression, data were analysed in conventional cohort and within-sibship analyses in which the association was examined within siblings discordant on education. Assuming that attenuation of associations in the within-sibship as compared with the cohort analyses would indicate confounding from factors shared within families.

RESULTS

A lower educational status was associated with a higher risk of cardiovascular disease, ischaemic heart disease and stroke. All associations attenuated in the within-sibship analyses, in particular in the analyses on ischaemic heart disease before age 45 years. For instance, in the cohort analyses, the hazard rate of ischaemic heart disease among women less than 45 years who had a primary school education was 94% (hazard ratio 1.94 (1.78-2.12) higher than among those with a vocational education, while it attenuated to 51% (hazard ratio 1.51 (1.34-1.71)) in the within-sibship analysis.

CONCLUSIONS

Confounding from factors shared by siblings explained the associations between education and the cardiovascular disease outcomes but to varying degrees. This should be taken into account when planning interventions aimed at reducing educational inequalities in the development of cardiovascular disease, ischaemic heart disease and stroke.

Education and coronary heart disease: mendelian randomisation study

Objective To determine whether educational attainment is a causal risk factor in the development of coronary heart disease.Design Mendelian randomisation study, using genetic data as proxies for education to minimise confounding.Setting The main analysis used genetic data from two large consortia (CARDIoGRAMplusC4D and SSGAC), comprising 112 studies from predominantly high income countries. Findings from mendelian randomisation analyses were then compared against results from traditional observational studies (164 170 participants). Finally, genetic data from six additional consortia were analysed to investigate whether longer education can causally alter the common cardiovascular risk factors.Participants The main analysis was of 543 733 men and women (from CARDIoGRAMplusC4D and SSGAC), predominantly of European origin.Exposure A one standard deviation increase in the genetic predisposition towards higher education (3.6 years of additional schooling), measured by 162 genetic variants that have been previously associated with education.Main outcome measure Combined fatal and non-fatal coronary heart disease (63 746 events in CARDIoGRAMplusC4D).Results Genetic predisposition towards 3.6 years of additional education was associated with a one third lower risk of coronary heart disease (odds ratio 0.67, 95% confidence interval 0.59 to 0.77; P=3×10^-8). This was comparable to findings from traditional observational studies (prevalence odds ratio 0.73, 0.68 to 0.78; incidence odds ratio 0.80, 0.76 to 0.83). Sensitivity analyses were consistent with a causal interpretation in which major bias from genetic pleiotropy was unlikely, although this remains an untestable possibility. Genetic predisposition towards longer education was additionally associated with less smoking, lower body mass index, and a favourable blood lipid profile.Conclusions This mendelian randomisation study found support for the hypothesis that low education is a causal risk factor in the development of coronary heart disease. Potential mechanisms could include smoking, body mass index, and blood lipids. In conjunction with the results from studies with other designs, these findings suggest that increasing education may result in substantial health benefits.

The importance of early life family factors in the association between cardiovascular risk factors and early cardiovascular mortality

Objective

To explore the importance of early life factors shared by siblings, such as parental socioeconomic position, parental practices, housing and neighbourhood, for the association between cardiovascular disease (CVD) risk factors and mortality from CVD, ischaemic heart disease (IHD) and cerebrovascular disease.

Methods

Norwegian health surveys (1974–2003) were linked with data from the Norwegian Family Based Life Course Study and the Cause of Death Registry. Participants with at least one full sibling among survey participants (n=2 71 643) were included. Data on CVD risk factors, body mass index (BMI), height, systolic blood pressure (SBP) and total cholesterol (TC) were stratified into ‘low’, ‘medium’ and ‘high’ risk, and smoking to ‘daily smoking’ and ‘not daily smoking’.

Results

Mean age of participants was 41 years, mean follow-up time was 19 years and during follow-up 2512 died from CVD. For each category of increased risk factor level, the per step HR of CVD mortality was increased by 1.91 (95% CI 1.78 to 2.05) for SBP, 1.67 (1.58 to 1.76) for TC, 1.44 (1.36 to 1.53) for BMI, 1.26 (1.18 to 1.35) for height and 2.89 (2.66 to 3.14) for smoking. In analyses where each sibship (groups of full siblings) had a group-specific baseline hazard, these associations were attenuated to 1.74, 1.51, 1.29, 1.18 and 2.63, respectively. The associations between risk factors and IHD mortality followed the same pattern.

Conclusion

Early life family factors explained a small part of the association between risk factors and mortality from CVD and IHD in a relatively young sample.

Volunteering and mortality risk: a partner-controlled quasi-experimental design

Background

The consensus that volunteering is associated with a lower mortality risk is derived from a body of observational studies and therefore vulnerable to uncontrolled or residual confounding. This potential limitation is likely to be particularly problematic for volunteers who, by definition, are self-selected and known to be significantly different from non-volunteers across a range of factors associated with better survival.

Methods

This is a census-based record-linkage study of 308 733 married couples aged 25 and over, including 100 571 volunteers, with mortality follow-up for 33 months. We used a standard Cox model to examine whether mortality risk in the partners of volunteers was influenced by partner volunteering status-something expected if the effects of volunteering on mortality risk were due to shared household or behavioural characteristics.

Results

Volunteers were general more affluent, better educated and more religious than their non-volunteering peers; they also had a lower mortality risk [hazard ratio (HR)adj = 0.78: 95% confidence interval (CI) = 0.71, 0.85 for males and HRadj = 0.77: 95% CI = 0.68, 0.88 for females]. However, amongst cohort members who were not volunteers, having a partner who was a volunteer was not associated with a mortality advantage (HRadj = 1.01: 95% CI = 0.92, 1.11 for men and HRadj = 1.00: 95% CI = 0.88, 1.13 women).

Conclusions

This study provides further evidence that the lower mortality associated with volunteering is unlikely to be due to health selection or to residual confounding arising from unmeasured selection effects within households. It therefore increases the plausibility of a direct causal effect.

Chronic low back pain and the risk of depression or anxiety symptoms: insights from a longitudinal twin study

BACKGROUND CONTEXT

Pain is commonly associated with symptoms of depression or anxiety, although this relationship is considered bidirectional. There is limited knowledge regarding causal relationships.

PURPOSE

This study aims to investigate whether chronic low back pain (LBP) increases the risk of depression or anxiety symptoms, after adjusting for shared familial factors.

STUDY DESIGN

This is a longitudinal, genetically informative study design from the Murcia Twin Registry in Spain.

PATIENT SAMPLE

The patient sample included 1,269 adult twins with a mean age of 53 years.

OUTCOME MEASURES

The outcome of depression or anxiety symptoms was evaluated with EuroQol questionnaire.

METHODS

Using logistic regression analyses, twins were initially assessed as individuals in the total sample analysis, followed by a co-twin case-control, which was partially (dizygotic [DZ] twins) and fully (monozygotic [MZ] twins) adjusted for shared familial factors. There was no external funding for this study and no conflict of interest was declared.

RESULTS

There was a significant association between chronic LBP and the risk of depression or anxiety symptoms in the unadjusted total sample analysis (odds ratio [OR]: 1.81, 95% confidence interval [CI]: 1.34-2.44). After adjusting for confounders, the association remained significant (OR: 1.43, 95% CI: 1.05-1.95), although the adjusted co-twin case-control was non-significant in DZ (OR: 1.03, 95% CI: 0.50-2.13) and MZ twins (OR: 1.86, 95% CI: 0.63-5.51).

CONCLUSIONS

The relationship between chronic LBP and the future development of depression or anxiety symptoms is not causal. The relationship is likely to be explained by confounding from shared familial factors, given the non-statistically significant associations in the co-twin case-control analyses.

The educational gradient in cardiovascular risk factors: impact of shared family factors in 228,346 Norwegian siblings

Background

Various indicators of childhood socioeconomic position have been related to cardiovascular disease (CVD) risk in adulthood. We investigated the impact of shared family factors on the educational gradient in midlife CVD risk factors by assessing within sibling similarities in the gradient using a discordant sibling design.

Methods

Norwegian health survey data (1980–2003) was linked to educational and generational data. Participants with a full sibling in the health surveys (228,346 individuals in 98,046 sibships) were included. Associations between attained educational level (7–9 years, 10–11 years, 12 years, 13–16 years, or >16 years) and CVD risk factor levels in the study population was compared with the corresponding associations within siblings.

Results

Educational gradients in risk factors were attenuated when factors shared by siblings was taken into account: A one category lower educational level was associated with 0.7 (95% confidence interval 0.6 to 0.8) mm Hg higher systolic blood pressure (27% attenuation), 0.4 (0.4 to 0.5) mmHg higher diastolic blood pressure (30%), 1.0 (1.0 to 1.1) more beats per minute higher heart rate (21%), 0.07 (0.06 to 0.07) mmol/l higher serum total cholesterol (32%), 0.2 (0.2 to 0.2) higher smoking level (5 categories) (30%), 0.15 (0.13 to 0.17) kg/m² higher BMI (43%), and 0.2 (0.2 to 0.2) cm lower height (52%). Attenuation increased with shorter age-difference between siblings.

Conclusion

About one third of the educational gradients in modifiable CVD risk factors may be explained by factors that siblings share. This implies that childhood environment is important for the prevention of CVD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-017-4123-0) contains supplementary material, which is available to authorized users.

Educational differences in cardiovascular mortality: The role of shared family factors and cardiovascular risk factors

AIMS

To explore the confounding effects of early family factors shared by siblings and cardiovascular risk factors in midlife on the educational differences in mortality from cardiovascular disease (CVD).

METHODS

Data from national and regional health surveys in Norway (1974-2003) were linked with data from the Norwegian Family Based Life Course Study, the National Educational Registry and the Cause of Death Registry. The study population consisted of participants with at least one full sibling among the health survey participants ( n=271,310). Data were available on CVD risk factors, including weight, height, blood pressure, total cholesterol and smoking.

RESULTS

The hazards ratio (HR) of CVD mortality was 3.44 (95% confidence interval (CI) 2.98-3.96) in the lowest educational group relative to the highest. The HRs were little altered in the within-sibship analyses. Adjusted for risk factors, the HR for CVD mortality in the cohort analyses was 2.05 (CI 1.77-2.37) in the lowest educational group relative to the highest. The respective HR in the within-sibship analyses was 2.46 (CI 1.48-2.24).

CONCLUSIONS

Using a sibling design, we did not find that the association between education and CVD mortality was confounded by early life factors shared by siblings, but it was explained to a large extent by CVD risk factors. These results suggest that reducing levels of CVD risk factors could have the greatest effect on mortality in less well-educated people.

Does education lower allostatic load? A co-twin control study

Many studies have found that education is associated with better health, but the causal basis of this association is unclear. The current study used a co-twin control design to examine if differences in years of education within twin pairs predict allostatic load. The strength of this design is that it controls for genetic and other familial confounds shared between twins. The sample consisted of 381 twins (with 292 twins from 146 complete pairs; mean age=57; 61% female) who participated in the biomarker project of the Midlife Development in the United States (MIDUS) study. Individual-level analyses showed a significant, negative association between years of education and allostatic load, but this association was explained entirely by familial influences shared between twins. The results of this study suggest that schooling does not itself protect against allostatic load.