Geography plays a big role in what is arguably the ultimate measure of health — longevity, especially among those with lower incomes, according to a new study published online by JAMA.

Specifically, lead author Raj Chetty, Ph.D., and colleagues found that higher income is associated with greater life expectancy, and differences in life expectancy across income groups increase. The association between longevity and income varied greatly across geographic areas, however.

“These are really enormous differences across places,” said Chetty, a Stanford University economist.

The researchers analyzed income data from 1.4 billion de-identified tax records and mortality data from Social Security Administration death records. Their analysis yielded four main findings:

  1. Higher income was associated with greater longevity at every level of the income distribution. And the gap between the richest 1% and the bottom 1% in the nation was vast. At 40, the richest men could expect to live to 87, whereas the bottom 1% had a life expectancy of just more than 72 years. Women had longer life expectancies than men, but the gap between genders narrowed substantially at higher income levels. Women at the top of the income distribution could expect to live close to 89 years, but the life expectancy of women at the bottom was 79 years.
  2. Inequality in life expectancy increased over time. Between 2001 and 2014, life expectancy increased by 2.3 years for men and 2.9 years for women in the top 5% of the income distribution, but it increased by only 0.3 years for men and 0.04 years for women in the bottom 5%.
  3. Life expectancy varied substantially across local areas. For those in the bottom income quartile, life expectancy differed by approximately 4.5 years between areas with the highest and lowest longevity. Changes in life expectancy between 2001 and 2014 ranged from gains of more than 4 years to losses of more than 2 years across areas.
  4. Geographic differences in life expectancy for individuals in the lowest income quartile were significantly correlated with health behaviors such as smoking and not exercising but were not significantly correlated with access to medical care, physical environmental factors, income inequality or labor market conditions. Life expectancy for those with low incomes was positively correlated with the local area fraction of immigrants, fraction of college graduates and local government expenditures per capita.

The study’s findings have implications for national policies like Social Security and Medicare, according to the authors. The fact that wealthier individuals generally have longer lifespans than poor individuals means that those with low incomes are paying into the system for a long time but don’t get to realize the benefits for as long. This reality is particularly important to discussions of raising the retirement age, according to the authors.

“If we think about a policy like indexing the retirement age to life expectancy, we need to think hard about which life expectancy we are talking about,” Chetty said. “If we just use average life expectancy in the United States, we are going to essentially start hurting the poor, especially in certain areas — like Detroit — relative to the rich.”

In a related commentary, Steven H. Woolf, M.D., M.P.H., and Jason Q. Purnell, Ph.D., M.P.H., argued that a “good life” is shaped by health, housing, the environment, safety,  education, employment, income and other factors. People working in those sectors should collaborate, and professional organizations should advocate among government and business officials, to help communities successfully address the social determinants of health, they said.

The issue contains two additional commentaries related to the research as well.