Where you live can impact how long you live.
Previous research has revealed a link between higher incomes and longevity, but the more complex picture is far from complete.
It remains unclear, for example, how the gaps between socioeconomic groups are changing over time, and what effect living in a specific place has on life expectancy.
The roles played by inequality, socioeconomic stress and differences in access to medicine are also subject to debate.
An additional question is whether a threshold exists above which additional income no longer makes a difference, or if there is an income level below which the impact on health does not continue to worsen.
Researchers, led by Raj Chetty, PhD, of Stanford University in California, have examined data enabling them to estimate life expectancy at 40 years of age by household income percentile, gender and geographic location. Location was based on "commuting zones," of which there are 741 in the US, each composed of several counties.
Widening gap revealed by recent figures
The team used new figures on income and mortality for the American population to evaluate factors associated with differences in life expectancy, after adjusting for race and ethnicity.
Income data for people aged 40-76 years came from 1.4 billion de-identified tax records for the period 1999-2014, and mortality data was from Social Security Administration death records.
Subjects were aged 53 years on average, and the median household income annually was $61,175, among those who were working.
There were 4,114,380 deaths among men, equivalent to a mortality rate of 596 per 100,000. Among women, there were 2,694,808 deaths, a mortality rate of 375 per 100,000.
Findings showed that people with a higher income were more likely to live longer. The difference in life expectancy between the richest 1% and poorest 1% was 14.6 years for men and 10.1 years for women.
Inequalities in life expectancy widened over time. From 2001-2014, the discrepancy increased by 2.3 years for men and 2.9 years for women in the top 5% of earnings. In the lower 5%, it increased by only 0.3 years for men and 0.04 years for women.
Life expectancy varied significantly between geographical areas. In the lowest 25% income group, there was a difference of some 4.5 years between areas with the highest and lowest life expectancy. Some areas gained more than 4 years over the study period, while others lost more than 2 years.
The impact of location
Geographic differences in the lowest income quartile were associated with health behaviors such as smoking, but not with access to medical care, the physical environment, income inequality or work-related conditions.
The life expectancy of people on a low income correlated with the proportion of immigrants and college graduates in the area, as well as local government spending.
Study authors suggest that local policy responses may be necessary to narrow the gaps.
"The strong association between geographic variation in life expectancy and health behaviors suggests that policy interventions should focus on changing health behaviors among low-income individuals. Tax policies and other local public policies may play a role in inducing such changes."
Social insurance programs should also take note, they say, as the figures indicate that redistribution of benefits across the community could be more effective.
Men and women in the top 1% of the income distribution can expect to claim Social Security and Medicare for 11.8 and 8.3 more years than those in the bottom 1%.
The report mentions an existing proposal to index the age of eligibility for Medicare and full Social Security benefits to increases in life expectancy. The authors call for such a policy to consider income and location as factors, if it is to maintain current levels of redistribution.
In one of three editorials, Angus Deaton, PhD, of Princeton University in New Jersey, remarks that the study "presents the facts in an extraordinarily comprehensive and complete way." However, he calls for further analysis to establish why income and health are so strongly related, and proposes including educational level on death certificates, to help inform future investigations.
Another editorial, by J. Michael McGinnis, of National Academy of Medicine in Washington, DC, stresses the community aspects of health equality and suggests a role for the study in developing community-wide public health approaches.
In a further comment, Dr. Steven Woolf, of Virginia Commonwealth University in Richmond, VA, and coauthors call for a "culture of collaboration" involving not only health workers, but also representatives from business leaders, education, the media and community groups among others.
Medical News Today reported recently on research indicating that health differences are widening among young people in rich countries.