While most Americans can look forward to living longer than ever, that’s not the case for white women who didn’t graduate from high school. Their life expectancy has actually dropped by five years — from 78 years in 1990 to 73 in 2008.

Graduation from high school can add years to your life. (Diana Reese for The Washington Post)

More heartening is the finding that black women without a high school diploma saw their life expectancy increase by a year from 73 to 74. In fact, they can now expect to live a year longer than their white counterparts.

The findings are from a study led by S. Jay Olshansky, a longevity researcher at the University of Illinois in Chicago, that looked at the disparities in life expectancy due to gender, race and education.

Published a year ago in the journal “Health Affairs” and funded by the MacArthur Foundation Research Network on an Aging Society, the research is making headlines again after a poignant and provocative piece in “The American Prospect” this week titled, “What’s Killing Poor White Women?”

The article examined the case of Crystal Wilson of Cave City, Ark., who dropped out of school in the ninth grade to marry. No, she wasn’t pregnant at the time. But by the age of 38, when she died unexpectedly, she was a mom and a grandmother, overweight and suffering from diabetes. She didn’t drink or smoke. Her death was attributed to “natural causes.”

Writer Monica Potts describes the drastic decline in longevity:

“It is an unheard-of drop for a wealthy country in the age of modern medicine. Throughout history, technological and scientific innovation have put death off longer and longer, but the benefits of those advances have not been shared equally, especially across the race and class divides that characterize 21st-century America. Lack of access to education, medical care, good wages, and healthy food isn’t just leaving the worst-off Americans behind. It’s killing them.

“It’s as if Americans with the least education are living in a time warp,” according to a video produced by the University of Illinois at Chicago, with life expectancy rates returning to those from the 1950s and 1960s; the least educated black men are living in 1954, black  women in 1962, white women in 1964 and white men in 1972.

The disparity in life expectancy at different educational levels has led to the formation of “at least two Americas,” Olshansky said, with “notably different longevity prospects” for each subgroup. White men with a college degree or higher educational level may live, on average, to age 80, compared to white males who did not graduate high school living to age 67. White college-educated women have a life expectancy of nearly 84, while white women without high school diplomas live to 73.

But why? Why, with all the advances in medicine and health care, are we seeing such a rapid decline in life expectancy for uneducated white women and men (who dropped three years from 70 to 67 from 1990 to 2008)?

The reasons are “unclear,” Olshansky e-mailed me, saying it’s all “speculation” at this point. All sorts of theories have been offered, but researchers have yet to prove any of them, he said.

He wonders whether obesity, a clear risk factor for African Americans, simply takes longer to contribute to fatal outcomes, while non-prescription drug use (think alcohol and meth) kills whites faster.

“But this is speculation,” he emphasized. “I have not seen a published explanation for this yet.”

In the meantime, the “obvious suggestion,” he said, is to raise education levels for all subgroups, which often correlates to higher employment and income and improved access to health care. (If nothing else, a higher income makes it easier to afford healthy food and gym memberships.) As of 2010, 5 percent of whites and 8 percent of African Americans between ages of 16 and 24 were not enrolled in school and did not have a high school diploma.

But Olshansky wasn’t quick to blame health-care access:

“I’m not sure the least educated members of the population are missing out on the advances in medical technology as much as they are adopting harmful behavioral habits that shorten their life. I’ve argued for quite some time that the only control we have over the duration of our lives is to shorten it, and we exercise that control often and with increased frequency (smoking, obesity, etc.).”

In other words, we can’t really do anything to lengthen our life span, but we sure can do things to shorten it.