A report issued last month by the Government Accountability Office shows that wealthier Americans, who are often able to delay receiving Social Security, are living longer and therefore collecting more money from the government.CREDITPHOTOGRAPH BY TETRA IMAGES / CORBIS

There may be no better way to appreciate humanity’s growing prosperity than to consider how long we live. A child born in 1900—little more than a century ago—was likely, on average, to die by the age of thirty. Today, according to theWorld Bank, the comparable figure is seventy-one. That is a worldwide average and so, of course, there is a considerable gulf between rich countries in Europe and Asia, where people live into their eighties, and the poorest nations in sub-Saharan Africa, where people born today will struggle to live to fifty. Nonetheless, even a child born in Chad, which has the world’s lowest life expectancy—49.81 years—will live two years longer than did the average white American male born in 1900.

Globally, the inequality in life expectancy is shrinking. Unfortunately, this effect, which the demographer Nicholas Eberstadt has aptly described as a “survival revolution,” does not apply to our country. Here,according to a studypublished in the most recent issue of the Journal of the American Medical Association (JAMA), the numbers are moving in the opposite direction.

It will surprise nobody to learn that life expectancy increases with income. Coming, however, in the midst of a Presidential campaign in which the corrosive effects of income inequality have been a principal debate topic, the data and its implications for public policy are particularly striking: the richest one per cent of American men live 14.6 years longer on average than the poorest one per cent. For women, the average difference is a just over ten years.

The gap appears to be growing fast. The researchers, led by Raj Chetty, a professor of economics at Stanford University, analyzed more than 1.4 billion federal tax returns, as well as mortality data from the Social Security Administration, from the years 2001 to 2014. In that period, the life expectancy of the richest five per cent of Americans increased by roughly three years. For the poorest five per cent, there was no increase.

What does a three-year difference mean? According to federal statistics cited in the study, eliminating every cancer death in the United States would add roughly three years to the average lifespan. For the richest Americans, then, the longevity increases of the past fifteen years have been the equivalent of curing cancer.

“To give you a sense of the magnitude’’ of the difference in life expectancy between rich and poor Americans, Chettytold NPR, “men in the bottom one per cent have life expectancy comparable to the average life expectancy in Pakistan or Sudan.’’

To the surprise of many experts, including those who did the research, the study found that the poorest Americans live considerably longer in some cities than in others. In New York, Los Angeles, and Miami, for example, the lowest quarter of income earners lived, on average, until the age of eighty-one. That’s only a few years less than the richest one per cent—and far longer than poor Americans in other regions. The cities with the shortest lifespans for the poor include Las Vegas, Tulsa, and Indianapolis.

Public-health officials often operate under the assumption that vast differences in access to health care would explain that kind of discrepancy. In this study, it didn’t. The report appears to have laid waste to another dogma: that poor people who live in America’s most stressful, crowded, and expensive cities face the biggest challenges to their health. At least with regard to how long one lives, the opposite appears to be true. People lived longer in cities, whether expensive or not, with highly educated residents, high incomes, and where local government invested in public health.

The reasons for the difference are not clear, although the authors point out that cities like New York often have aggressive anti-smoking policies and make it harder for people to eat trans fats, and drink sugary sodas—which are implicated in common diseases like obesity and diabetes.

The findings are sure to offer ammunition to those who argue for greater investment in community and public health. “Amid the excitement over personalized medicine,’’Steven H. Woolf and Jason Q. Purnell wrote in an accompanying editorial, “the fact remains that a patient’s zip code may be more useful for targeting therapy than his or her genotype. The ability of patients to understand, personalize, and implement treatment plans is influenced by their education, language, literacy, and neighborhood resources.’’

The longevity gap between rich and poor has already begun to have a profound effect on Social Security, according to aGovernment Accountability Officereport that was issued last month. Americans are entitled to receive retirement benefits at the age of sixty-two. But many wait to retire (benefits must begin by age seventy), and those who do wait earn bigger Social Security checks. Since those who are able to wait are often richer they also tend to live longer and therefore will collect more money from the government.

The formula for calculating monthly Social Security benefits is supposed to be progressive. Payments are meant to provide a proportionally larger monthly income for lower earners than for higher earners. However, when viewed in terms of benefits received over a lifetime, the disparities in life expectancy across income groups nullify the progressive effect of the program: the rich collect payments for years longer. In other words, a growing share of Social Security benefits will go to people with higher incomes and a shrinking share are going to those with lower incomes.

Such disparities may reshape the very foundation of American social-welfare policy. “A medical journal article reporting that income is significantly associated with life expectancy is a call to arms,’’ the authors of the editorial inJAMAwrote, “ but the answer cannot come from medicine or public health alone.’’ Instead, it will have to come from the realm of politics. And until such answers begin to be translated into laws, two things are certain to keep growing: the prosperity of rich Americans, and the suffering of the poor.