Their findings throw cold water on the good news that Americans' lives have been getting longer. Life expectancy at birth, they found, "is rising in absolute terms but falling relative to other countries."*

Here's the chart for men, with the U.S. shown as red dots that are gradually slipping in rank among their peers:

The National Academies Press

It's an even more dramatic story for women:

The National Academies Press

Then the authors went even deeper, looking at the probability of someone from a given country living to age 50. American men, they found, have historically ranked low among all countries when it comes to their likelihood of making it to old age. But what they found for women was even worse news: "Over the past 10 years, only the United States has failed to make significant improvements in the probability of survival up to age 50 for women," they wrote.

You can see American women (the red dots) trailing further and further from the pack each year:

The National Academies Press

"In 1980, the United States was ranked 11th on this measure; by 1990 it had fallen to 13th and by 2006 had dropped to 21st," they wrote.

The findings dovetail with other recent research that shows that in half of U.S. counties, life expectancy is getting worse: Today's women are not living as long as their mothers once did, as Grace Wyler described in The Atlantic last year.

Health Affairs/The Population Institute, University of Wisconsin

Some public-health researchers think more and better healthcare is the answer. Longevity in the Netherlands also stagnated in the 1980s, for example, but skyrocketed from 2002 to 2008 after the country began dumping money into the healthcare system.

Others think the cause is poverty, and underpinning that, inadequate education. Less-educated women are less likely to have jobs, and therefore they may not only struggle to afford doctors' visits and healthier lifestyles, but also may lack the strong social networks and sense of purpose that have shown to reduce mortality. At the Metrotrends Urban Institute blog, Aron writes, "Our preliminary analyses suggest that increases in mortality are especially pronounced among white women of reproductive age, not a group we generally think of as being disadvantaged." A 2012 Health Affairs study found that this drop in longevity has been especially dramatic for white high-school dropouts, who are now expected to die five years younger than the previous generation.

Past research has shown that Americans without high-school diplomas are at greater risk for nearly every kind of health issue, and while racial differences in life span persist even among college graduates, better-educated people of every race tend to live longer.

The debate over whether and how poverty causes poor health is endless, but the speed at which the U.S. is losing ground in women's health is worrisome. Sure, less-educated women have less money for healthy food and gym memberships, but those behaviors might be symptoms of larger failings in low-wage jobs, the healthcare system, and public policy.

*The countries included in the analysis were Australia, Austria, Belgium, Canada, Denmark, Finland, France, Iceland, Ireland, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, the United States, and West Germany.