Income inequality in the United States has increased substantially over the last three decades, with overall levels of inequality dangerously approaching the extreme level that prevailed prior to the Great Depression. Despite generous stipends such as stimulus checks, the pandemic will likely only widen the gap between the rich and the poor.

But while income inequality and the pressure on the social fabric are important topics of research, not nearly enough attention has been given to wealth disparities, which are far greater and growing at a faster rate than income inequality in the United States. Wealth inequality is particularly important in the context of population health and longevity.

Individuals with greater wealth are better equipped to access medical care, safe places to work and exercise, fresh foods, and are more protected against economic shocks, such as losing a job, unexpected medical emergencies, and other financial crises.

While the impact of wealth on health, in general, cannot be denied, just how much it matters has always been unclear due to a murky environment of confounding factors such as upbringing, genetics, education, and lifestyle choices. Do wealthy individuals tend to live longer by virtue of their financial status alone or do people with a healthy lifestyle, good genetics, or supportive parents tend to both live longer and make more money? Hard to say.

Every additional $50,000 of net worth reduces your risk of death by 5%

This is where a new study from Northwestern University might come in handy. Unlike other studies before it that investigated the effects of a person’s net worth — the difference between a person’s total financial assets and their liabilities — this time, the researchers included siblings and twin pair data. This allowed the researchers to minimize the effect of genetics and upbringing, and focus on how wealth impacts longevity.

For their study, the researchers accessed the Midlife in the United States (MIDUS) project, a longitudinal study on aging that was first established in 1989. The study included nearly 5,400 adults who between 1994 and 1996 had an average age of 46.7 years and a mean net worth of $122,153. Approximately half of the participants were ‘singletons’ (individuals with no siblings), while about 2,490 participants were grouped into siblings and twin pairs. A follow-up was performed 24 years later to see how many of the initial participants were still alive and what their health condition was.

The researchers used survival models to analyze the association between net worth and longevity. They found that, across the entire sample, and regardless of whether or not they had any brothers or sisters, net worth was associated with lower mortality risk.

Specifically, the researchers found that for every additional $50,000 of net worth accumulated at midlife, the risk of death later in life dropped by 5%.

Things were more interesting when comparing longevity in siblings and twin pairs. The researchers found that the sibling or twin with more assets under their names lived considerably longer than their less well-off co-sibling/twin.  A difference of $139,000 in net worth was associated with a 13% relative decrease in the probability of death nearly 24 years later, favoring the family member with a higher net worth, the researchers noted in their study published in JAMA Health Forum.

“The within-family association provides strong evidence that an association between wealth accumulation and life expectancy exists, because comparing siblings within the same family to each other controls for all of the life experience and biology that they share,” said corresponding author Eric Finegood, a postdoctoral fellow in the Institute for Policy Research at Northwestern.

It may be possible that individuals with serious health conditions, such as heart disease or cancer, could find themselves incapable of accruing significant wealth due to healthcare costs and work limitations. But when the Northwestern researchers ran the models again using only a sample of individuals without cancer or heart disease, the within-family association between wealth and longevity remained valid.

“Far too many American families are living paycheck to paycheck with little to no financial savings to draw on in times of need, said Greg Miller, the Louis W. Menk Professor of Psychology and faculty fellow at the Institute for Policy Research at Northwestern. “At the same time, wealth inequality has skyrocketed. Our results suggest that building wealth is important for health at the individual level, even after accounting for where one starts out in life. So, from a public health perspective, policies that support and protect individuals’ ability to achieve financial security are needed.”