There's new research out today that shows the life expectancy gap between the rich and the poor in America is wide and growing — but not necessarily inevitable.

For the study, published today in JAMA, a group of researchers led by Stanford University economist Raj Chetty analyzed income data for the US population from 1.4 billion tax records between 1999 and 2014. They then compared it with mortality data from Social Security Administration death records.

What they found was a startling divide in longevity between America's richest and poorest. Men who were among the top 1 percent of income earners lived 15 years longer than men at the bottom 1 percent. For women at the extremes of the income distribution, life expectancy differed by 10 years.

This inequality has also gotten worse over time. "Between 2001 and 2014," the researchers wrote, "life expectancy increased by 2.3 years for men and 2.9 years for women in the top 5 percent of the income distribution, but increased by only 0.3 years for men and 0.04 years for women in the bottom 5 percent." And compared with other wealthy countries, the extremes are more extreme: Life expectancy here is lower and disease morbidity is higher.

Health and longevity gaps aren't inevitable

But there's evidence that the gaps aren't inevitable and vary significantly from region to region.



For examples, in some cities the disparities in life expectancy were smaller. For people in the bottom income quartile, the top cities when it came to life expectancy were New York, Santa Barbara, San Jose, Miami, and Los Angeles. In these places, the mean life expectancy among the bottom 25 percent of earners was about 81 — or four or five years less than those at the top 25 percent.

The worst cities for longevity among the poorest were Tulsa, Indianapolis, Oklahoma City, Las Vegas, and Gary, Indiana. There, the people at the bottom income quartile lived to 77, or about seven to nine years less than the richest folks.

Why such huge socioeconomic and geographical differences in longevity?

Turns out that's very hard to answer. The researchers considered various theories, and they found limited evidence for any of them.



"One such theory is that health and longevity are related to differences in medical care," they wrote. But they found little support for this idea: Life expectancy among poor folks was not significantly correlated with worse health care quality or coverage.



They also weren't able to demonstrate that factors in the physical environment (such as air pollution) in poorer areas might be shortening people's lives, or that the unequal life spans were related to a lack of social cohesion or local labor market conditions.



"None of the four theories for shorter life expectancy among low-income individuals was consistently supported by the data," the researchers summed up.



Instead, Harvard economist David Cutler, one of the study authors, pointed out the strongest pattern they uncovered was that low-income individuals lived the longest (and had more healthy behaviors) in places with well educated, high-income populations, as well as generous government spending.



So, contrary to theories that extreme inequality can lower life expectancy, especially for the poor, the researchers found that cities with a lot of rich people — like New York and San Francisco — actually had poor people who lived longer.



The researchers aren't entirely sure why, and called for more research. They do, however, suspect that it has to do with health-promoting public policies and better-funded public services in rich cities.



For example, they found the geographic differences in life expectancy for the poorest folks were "significantly correlated" with health behaviors like smoking. Smoking bans, cigarette taxes, and anti-obesity efforts (such as the ban on trans fats or calorie labeling requirements) in cities like New York may have had a net positive effect on the health of the local population — including the lowest-income people.

"A different theory," Cutler said, "is who you're around effects your health." So there may be some social contagion of healthy behaviors at work. "If you're in New York City or San Francisco, where fewer people are smoking, it's just not as pleasurable to smoke," he added.

Any future research that can answer this question will be a major step toward addressing health inequalities. For now, Cutler guesses "it's some combination of formal public policies and the effect that comes when you're around fewer people who have behaviors like smoking, and therefore you smoke less."

"Inadequate income is jeopardizing US life expectancy"

In an accompanying editorial, Steven Woolf, director of Virginia Commonwealth University's Center on Society and Health, and Jason Purnell of Washington University in St. Louis noted that the study's most important implication is that "inadequate income is jeopardizing US life expectancy. "

They write that this should be a call to action for physicians to not only consider how social status and income may affect their patients' health, but also to reach beyond medicine and work with others across sectors in order to improve the health of populations.

"Clinicians and health care systems find it unrealistic and overwhelming to tackle complex social problems, but they are not alone," Woolf and Purnell write. "Teachers, police officers, parents, employers, and many others also feel powerless to solve social problems without partners. Meaningful change requires broader thinking. ... As the history of tobacco control teaches, multilevel interventions across the socioecological framework— from legislation to marketing — are essential to advance population health."