Researchers are blaming drugs, alcohol and suicide for a troubling increase in the mortality rate among a large group of white men and women in middle age. Another deadly factor in the trend could well be economic.

Demographers have long known that wealthier people tend to live longer than the poor -- it's one of the many advantages of affluence.

And while the authors of a new study examining recent pattern in mortality did not directly consider levels of income, they did consider levels of educational attainment, often used by researchers to estimate a person's social class.

They found that among white men and women between the ages of 45 and 54 without a college degree, the rate of death has increased since 1999, a reversal after decades of improvement. Had the mortality rate continued to decline, roughly half a million people in this group who died between 1999 and 2013 would still be alive today. That number of early deaths is comparable to the toll of AIDS in the United States, according to the authors.

In several similar countries, the rate of death continued to decline over the 14 years of the study, as it did among better educated white U.S. men and women.

The black and Hispanic mortality rates are also declining in the United States, although the black rate is still higher than the white mortality rate.

The authors of the study are Princeton University economists Anne Case and Angus Deaton, her husband, who was named a Nobel laureate last month. They find that suicides, overdoses, and liver diseases associated with heavy, chronic drinking are among the reasons for the increasing frequency of death among white men and women in middle age.

That these conditions are concentrated among this particular group of Americans with modest education suggests that the broader economic opportunities that come with higher education can somehow alleviate the stresses and anxieties of middle age.

Income for typical Americans have declined since reaching an apex in 1999, the same year in which the study found mortality rates reversed. And a recent report predicted that men who turned 50 in 2010 could expect to live to 89 if they were in the richest group of Americans, but only to 76 if they were in the poorest group.

Researchers are still trying to understand the exact connections between income, education, and overall health. What does seem clear is that for many Americans, social class can determine not just the kind of life you live but for how long you live it.