Why is life expectancy dropping for low-educated white Americans?

Reader Norm sent me a link to this news article that reported on a new study that said that life expectancy had dropped dramatically for white people who did not have much formal education.

The steepest declines were for white women without a high school diploma, who lost five years of life between 1990 and 2008… By 2008, life expectancy for black women without a high school diploma had surpassed that of white women of the same education level, the study found.

White men lacking a high school diploma lost three years of life. Life expectancy for both blacks and Hispanics of the same education level rose, the data showed. But blacks over all do not live as long as whites, while Hispanics live longer than both whites and blacks.

Although a rise in life expectancy is the norm, dramatic declines over a short period are not unprecedented. But they are usually identified with wars, famines, or major social upheavals like the seven-year drop for Russian men following the collapse of the Soviet Union.

Needless to say, this new result has set off a scramble to find explanations, with initial speculations based on correlations. Given that there have been a lot of changes in the last two decades, there is no shortage of ideas. Some have suggested an increase in risky behaviors such as abuse of prescription drugs and smoking. Others have suggested that people have less access to health care and more people have to go to work.

Kathleen Geier at The Washington Monthly points to other studies that suggest that it could be due to rapidly rising income inequality.

But the real puzzle is why this is causing a decline among white people only. When socio-economic data is disaggregated by race and ethnicity, it is almost always the case that blacks and Hispanics do worse. If rising income inequality is the cause, why are the minority groups able to still increase their life expectancy despite bearing a disproportionate share of its negative effects?