Researchers have long established that people who earn lower incomes live measurably shorter lives than their better-off counterparts. But disturbing new findings from the Brookings Institution indicate that the “longevity gap” between the rich and the poor in the United States has grown dramatically wider in recent years.

Researchers Barry Bosworth, Gary Burtless, and Kan Zhang analyzed data from the Census Bureau’s Survey of Income and Program Participation, Social Security Administration, and Health and Retirement Study to provide details about the incomes and lives of over 100,000 men and women born between 1910 and 1950. According to their findings, “the mortality differential is growing over time.”

Just how significantly? The average life expectancy of men who were born in 1920, survived to age 50 and are at the top 10 percent of earners is 79.3 years. Their counterparts in the bottom 10 percent are expected on average to live five years fewer, the study finds.

Fast forward to men born in 1940 and you find a longevity gap of 12 years between the top and bottom 10 percent. This gulf is even wider for men born in 1950, expanding to a 14-year difference in life expectancy.

It's no different for female populations. Among women born in 1920 who survived to age 50, the longevity gap was 4.7 years. That widened to a gulf of 13 years for those born in 1950.

Meanwhile, for the lowest earners, average life expectancy is barely improving. Researchers found that the bottom 10 percent of male earners born in 1920 are expected to live to 72.9 years. That same demographic born in 1950 is expected live to the age of 73.6 on average.

Women in the lowest income group, meanwhile, made “no gain at all” in life expectancy, the researchers concluded. Top earners, in contrast, saw an improvement of 6.4 years.

While the Brookings Institution is hardly a paragon of progressive economic policy, its findings come amid growing concerns about inequality, from the debate in the 2016 presidential election cycle to growing low-wage worker movements demanding a $15 minimum wage.

While the Brookings examination does not include an in-depth analysis of race, other studies show a profound life expectancy gap between white and black people in the United States. One study published by Health Affairs in 2014 found that the gulf has diminished slightly between 1990 and 2009. However, it remains wide: at 5.4 years for males and 3.8 years for females.