Greater personal wealth very clearly correlates with modestly greater longevity. Why is this? That is a hard question to answer, as the network of correlations between socioeconomic status, education, wealth, intelligence, and lifestyle choices are challenging to pick apart in most available databases of epidemiological information. Are wealthier people on balance more educated, and more educated people tend to take better care of their health? Are wealthier people wealthy because they tend to be more proactive in all aspects of life, and thus also make better use of the opportunities provided by medical technology? Are wealthier people better equipped culturally by their upbringing to take better care of their health? Does greater intelligence, and thus greater capacity to become wealthy, derive from gene variants that also produce physical robustness and a longer life span? And so forth.
The study here is interesting for looking into the correlation between personal wealth and the later life survival of siblings and twins, as well as a more general population. Comparing siblings can eliminate many of the questions regarding, for example, the effects of upbringing in a wealthier environment on lifestyle choice, or the possibility of pleiotropic effects of genetic variants on both intelligence and physical robustness. The researchers find that wealth effects on longevity, whatever the underlying cause, appear to be much the same between siblings and non-siblings. This by no means points to a definitive explanation for the correlations observed, but it does make some of the existing hypotheses less likely to be true.
Socioeconomic disparities in life expectancy are substantial in size. Financial wealth or net worth, which is the value of an individual's assets (such as savings, real estate, and vehicles) minus liabilities, is directly associated with longevity. However, a challenge in this area of research has been eliminating or minimizing the potential for confounding by the early environment and heritable traits, either of which could simultaneously affect socioeconomic conditions in adulthood and health in the course of life.
Full siblings who were raised in the same family share much of their early rearing environment and are genetically related to one another. Thus, in sibling-comparison studies, factors that are shared between siblings are controlled. Twin comparisons provide an even greater control of family-level early-life confounding and, in the case of monozygotic (MZ) twins, control for all heritable genetic factors. Previous research found that discordance in occupational prestige was associated with cardiovascular risk and overall mortality; twins with lower-prestige jobs had worse health on both outcomes compared with their co-twins with higher-prestige jobs. This pattern suggests that socioeconomic disparities in health are affected by experiential factors in adulthood over and above any potential confounders that involve the siblings' shared early environment and genetic characteristics. In other discordant sibling and twin analyses, educational attainment and composite measures of adult socioeconomic position also have been associated with better adult health outcomes and longevity. However, results from these and other studies that used different methods do suggest these associations may be partially explained by shared family-level environmental factors or genetic predispositions.
Comparatively little attention has been given to wealth disparities, a potentially important oversight. In this cohort study, we used a discordant sibling design to conservatively estimate the association between wealth and longevity. Specifically, we aimed to identify the association between net worth at midlife (the middle years of life) and subsequent all-cause mortality in individuals as well as within siblings and twin pairs. We posed two research questions. First, was wealth accumulation at midlife associated with longevity over a nearly 24-year follow-up? Consistent with previous work, we expected that higher wealth accumulation would be associated with increased longevity. Second, was the wealth-longevity association present over and above controls for family and heritable factors that could confound this association?
In this cohort study of 5,414 participants in the Midlife in the United States study, those who had accumulated a higher net worth by midlife had significantly lower mortality risk over the subsequent 24 years. In sibling and twin comparison models that controlled for shared early life experiences and genetic influence, the association between net worth and longevity was similar in magnitude. Thus net worth at midlife was associated with longevity among adults in the study, and this association is unlikely to be merely an artifact of early experiences or heritable traits shared by families.