In an elegant analysis of Midlife in the United States (MIDUS) cohort data, Finegood et al1 show that greater wealth in midlife is associated with lower mortality during the next 24 years. Moreover, the authors show that the association is similar even when it is estimated based only on comparing siblings, dizygotic twins, or monozygotic twins within families. The authors conclude that the association of wealth with mortality is therefore not attributable to early life or genetic factors, both of which have been posited as confounders of the associations between wealth in adulthood and mortality later in life.
The analytical approach used by Finegood et al1 cleverly disentangles levels of family wealth from within family deviations in wealth for each sibling or twin. By focusing on the effect of within-family deviations, they are able to hold family factors, including family wealth, constant. The beauty of this is that it presumably holds constant heritable and early environment factors that may be associated with wealth acquisition and health. (I say presumably because, as Finegood et al1 note, this is not perfect because there may be differences in the early circumstances of siblings, even with twins.) In using this analytical approach, the research question is narrowed to the following: are within-family differences in wealth associated with within-family differences in mortality? This method has the potential advantage of strengthening the ability to draw causal inferences.
Several methodologists have commented on the strength and weaknesses of sibling and twin designs, including what they gain and lose by conditioning on family.2,3 Finegood et al1 discuss several of these challenges and also note the limitations of their sample, which is predominantly composed of (more than 90%) White individuals. Because of their sample, they are not able to investigate the effect of wealth differences comparable in magnitude with the stark differences observed, for example, between Black and White individuals in the US, differences that result from a long history of systemic racism. The median wealth in the sample is $122 000 compared with national data for 2019 of $189 000 for White individuals and $24 000 for Black individuals.4 It is plausible that the health consequence of moving from an already high to a higher level of wealth is smaller than what we would observe by increasing wealth among those who have little or no wealth at all.
Finegood et al1 carefully address a narrow and specific question: are differences in wealth that emerge in adulthood (ie, that are independent of family factors, including family wealth) associated with subsequent differences in mortality? They endeavor to use a design and analytical approach that allows them to disentangle the possible effects of wealth in adulthood from genetic and other family factors, including early environment factors. They carefully note the possibility that unaccounted for factors or experiences would still confound the within-family associations between wealth and mortality. Despite these caveats, and the challenges in drawing causal inferences regarding the effects of specific interventions from these types of analyses, their results suggest, as they note, that increasing wealth among adults could benefit their health.
But the results reported by Finegood et al1 also raise questions about how we should think about the underlying causes of health inequities and what we should do about them. Interestingly, Finegood et al1 show that in models that pool siblings and twins, higher family wealth (proxied by the average wealth of the siblings or twins) is also associated with mortality independently of within-family deviations in wealth and other individual-level factors that are included in their analysis. Their study was not designed to investigate the health consequences of family wealth (and other family factors that are correlates or consequences of family wealth could contribute to this association), so they understandably do not dwell on this result. Nevertheless, the presence of a family wealth effect highlights the many ways in which inequities in wealth might affect health, not only through the health consequences of the wealth that individuals may acquire during their lives (independently of their family wealth, the main focus of Finegood et al1), but also through the long, pervasive, and profound effects of the intergenerational transmission of wealth.
Given what we know about how wealth is sustained and enhanced across generations, and also the many ways in which wealth affects exposures, opportunities, and access to resources that are relevant to health,5 I would surmise that the intergenerational transmission of wealth and its many consequences (including its association with early life and beyond) has a more profound association with population health than the wealth acquired by individuals during their lives (be it a function of individual ability, opportunities, or sheer luck) independently of their family circumstances. The fundamental driver is economic inequality and its many consequences over the life course and across generations, inequality that arises from the history and systems embedded in our society.
Studying the effect of social and economic factors like wealth is much more complex than studying a drug or even a behavior or medical intervention. This is because the factors we are studying are broad, operate over long periods (even across generations), and through many different and often changing mechanisms. In our quest to build evidence for the effects of these factors, we often understandably narrow the questions and focus them on specific groups or samples. We need studies like those of Finegood et al1 and many others that valiantly grapple with the complexities involved, breaking them down into pieces. But then the task is to put Humpty-Dumpty back together again and pull together different kinds of imperfect and partial evidence, draw inferences, propose policies, and then learn by evaluating those policies. We have enough evidence from multiple sources to know that inequality (including wealth inequality) is a key driver of population health and of the stark disparities in health by race and class present in our society. The question now is, can we act on this knowledge?
Corresponding Author: Ana V. Diez Roux, MD, PhD, MPH, Dana and David Dornsife Dean, Dornsife School of Public Health, 3215 Market St, 2nd Floor, Room 256, Philadelphia, PA 19104 (Avd37@drexel.edu).
Published: July 23, 2021. doi:10.1001/jamahealthforum.2021.1647
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Diez Roux AV. JAMA Health Forum.
Conflict of Interest Disclosures: None reported.
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Diez Roux AV. The Pervasive Influence of Wealth Inequality on Health. JAMA Health Forum. 2021;2(7):e211647. doi:10.1001/jamahealthforum.2021.1647