People with 12 years of education or more have seen their life expectancy rise faster than among those with less education, and researchers say that differences in smoking rates are an important reason for the disparity.

Science Daily reported March 12 that researchers from Harvard Medical School and Harvard University studied death-certificate data and information from the National Longitudinal Mortality Study gathered between 1981 and 1988, and between 1990 and 2000. They found that in both data sets life expectancy rose among those with 12 years or more of education, while it plateaued among individuals with less education.

Bottom line: as of 2000, better-educated 25-year-olds could expect to live to age 82, while less-educated adults of the same age could only expect to live to 75.

Smoking-related illnesses accounted for much of the mortality gap, researchers found. Lung cancer and chronic obstructive pulmonary disorder alone accounted for 20 percent of the mortality differences between the two groups. Past studies have shown that less-educated people are also less likely to quit or abstain from smoking.

"We like to think that as we as a country get healthier, everyone benefits," said study co-author David Cutler. "Here we've found that you can have a rising tide that only lifts half the boats -- and the ones lifted are the ones doing better to begin with."

The study appears in the March/April 2008 issue of the journal Health Affairs.