Experts have long known that rich people generally live longer than poor people. But a growing body of data shows a more disturbing pattern: Despite big advances in medicine, technology and education, the longevity gap between high-income and low-income Americans has been widening sharply.

The poor are losing ground not only in income, but also in years of life, the most basic measure of well-being. In the early 1970s, a 60-year-old man in the top half of the earnings ladder could expect to live 1.2 years longer than a man of the same age in the bottom half, according to an analysis by the Social Security Administration. Fast-forward to 2001, and he could expect to live 5.8 years longer than his poorer counterpart.

New research released Friday contains even more jarring numbers. Looking at the extreme ends of the income spectrum, economists at the Brookings Institution found that for men born in 1920, there was a six-year difference in life expectancy between the top 10 percent of earners and the bottom 10 percent. For men born in 1950, that difference had more than doubled, to 14 years.

For women, the gap grew to 13 years, from 4.7 years.

"There has been this huge spreading out," said Gary Burtless, one of the authors of the study.

The growing chasm is alarming policymakers, and has surfaced in the presidential campaign. During the Democratic debate Thursday night, Bernie Sanders and Hillary Clinton expressed concern over shortening life spans for some Americans.

"This may be the next frontier of the inequality discussion," said Peter Orszag, a former Obama administration official now at Citigroup, who was among the first to highlight the pattern.

The causes are still being investigated, but public health researchers say that deep declines in smoking among the affluent and educated may partly explain the difference.

Overall, according to the Brookings study, life expectancy for the bottom 10 percent of wage earners improved by just 3 percent for men born in 1950 compared with those born in 1920. For the top 10 percent, though, it jumped by about 28 percent. (The researchers used a common measure — life expectancy at age 50, and included data from 1984 to 2012.)

It is hard to point to one overriding cause, but public health researchers have a few answers. In recent decades, smoking, the single biggest cause of preventable death, has helped drive the disparity, said Andrew Fenelon, a researcher at the Centers for Disease Control and Prevention. As the rich and educated began to drop the habit, its deadly effects fell increasingly on poorer, uneducated people. Fenelon has calculated that smoking accounted for a third to a fifth of the gap in life expectancy between men with college degrees and men with only high school degrees. For women it was as much as a quarter.

Obesity, which has been sharply rising since the 1980s, is more ambiguous. The gap between obesity rates for high earners and low earners actually narrowed from 1990 to 2010, according to an analysis by the National Academy of Sciences. By 2010, about 37 percent of adults at the lower end of the income ladder were obese, compared with 31 percent of those at the higher end.

More recently, the prescription drug epidemic has ravaged poor white communities, a problem that experts said would most likely exacerbate the trend of widening disparities.

Limited access to health care accounts for surprisingly few premature deaths in America, researchers have found. So it is an open question whether President Barack Obama's health care law — which has sharply reduced the number of Americans without health insurance since 2014 — will help ease the disparity.

At the heart of the disparity, said Elizabeth H. Bradley, a professor of public health at Yale, are economic and social inequities, "and those are things that high-tech medicine cannot fix."

Life expectancy for the bottom 10 percent of male wage earners born in 1920 was 72.9, compared with 73.6 for those born in 1950, the Brookings researchers found. For the top 10 percent, life expectancy jumped to 87.2 from 79.1.

The growing longevity gap means that benefits like Social Security are paid out even more disproportionately to the better-off, because they are around for more years to collect them. Last summer, the National Academy of Sciences convened a panel of experts to study the implications. It concluded that disparate life expectancies are making the country's biggest entitlement programs, like Social Security and Medicare, increasingly unfair to the poor and suggested officials consider policy changes to address the problem.

Poor health outcomes for low-income Americans have dragged the United States down to some of the lowest rankings of life expectancy among rich countries. The Social Security Administration found, for example, that life expectancy for the wealthiest American men at age 60 was just below the rates in Iceland and Japan, two countries where people live the longest. Americans in the bottom quarter of the wage scale, however, ranked much further down — one notch above Poland and the Czech Republic.

"It's embarrassing," Bradley said.

Some researchers noticed a pattern of diverging longevity in the 1990s, but many were doubtful, saying that it could be a statistical blip and that the data was not strong enough. The evidence continued to gather, but many researchers remained skeptical. In late 2007, researchers from the Social Security Administration identified the pattern in a large trove of earnings and death data. Now most researchers agree that the change is real.

Many researchers believe the gap in life spans from lower- to upper-income Americans started widening about 40 years ago, when income inequality began to grow. Earlier in the 20th century, trends in life spans were of declining disparities, some experts say, because improvements in public health, such as the invention of the polio vaccine and improved sanitation, benefited rich and poor alike. The broad adoption of medication for high blood pressure in the 1950s led to a major improvement for black men, erasing a big part of the gap with whites, said Dana P. Goldman, the director of the Leonard D. Schaeffer Center for Health Policy and Economics at the University of Southern California. But medical improvements can also drive disparity when they disproportionately benefit affluent Americans; for example, cutting-edge cancer treatments.

The experience of other countries suggests that disparities do not necessarily get worse in contemporary times. Consider Canada, where men in the poorest urban neighborhoods experienced the biggest declines in mortality from heart disease from 1971 to 1996, according to a 2002 study. Overall, the gap in life expectancy at birth between income groups declined in Canada during that period. And a study comparing cancer survival rates found that low-income residents of Toronto had greater survival rates than their counterparts in Detroit. There was no difference for middle- and high-income residents in the two cities.

"There are large swaths of the population that are not enjoying the pretty impressive gains the rest of us are having in life spans," said Christopher J.L. Murray, director of the Institute for Health Metrics and Evaluation in Seattle. "Not everybody is sharing in the same prosperity and progress."