While most Americans assume that their children will live longer than they do, a growing body of evidence suggests this isn't true for everyone. The latest piece of evidence is a study by Jay Olshansky, a public health professor at the University of Illinois at Chicago, who found that life expectancy for people with less than a high school diploma decreased by four years between 1990 and 2008.

Olshansky also found that the declines were most pronounced among white women who did not graduate from high school. He says their life expectancy decreased by five years. White men lacking a high school diploma, by comparison, lost three years of life expectancy. Olshansky's data also showed that life expectancy for both blacks and Hispanics who did not graduate from high school actually increased.

Why are women with little education living shorter lives? Olshanksy's team couldn't pin down the exact cause but speculated that the decline may be related to increases in "prescription drug overdoses among young whites, higher rates of smoking among less educated white women, rising obesity, and a steady increase in the number of the least educated Americans who lack health insurance," according to a report by The New York Times.

A new study by Harvard University sheds some light on the trend. Researchers at the Harvard Center for Population and Development Studies found that the two factors most strongly associated with uneducated women's shorter life expectancies are smoking and not having a job.

Jennifer Karas Montez, who led the Harvard study, and her team used health surveys conducted by the National Center for Health Statistics, drawing on data from about 47,000 women ages 45 to 84, according to The New York Times. "The study weighed more than a dozen factors to see which were causing the divergence in mortality rates. Poverty, obesity, homeownership, marital status and alcohol consumption were among the factors investigated," according to the Times.

None of these factors had much impact, according to Montez. Not surprisingly, smoking did impact life expectancy but the only other factor that had any measurable impact on life span was joblessness.

"But the study raised more questions than it answered, in particular about why employment status affects physical health," reported The New York Times. Montez said there is some evidence that "having a job offered intangible benefits that could improve health, including a sense of purpose and control in life, as well as providing networks that help to reduce social isolation."