College-educated people live seven years longer on average than those who never went beyond high school, according to a Harvard University researcher.

Those who were 25 in 2000 and better educated could expect to live to the age of 82, compared with age 75 for those less educated, according to research in the journal Health Affairs. Smoking-related illnesses were more prevalent in the group with less education, accounting for about one-fifth of the mortality difference, the study found.

This is the first study based on education to examine life expectancy trends over 10 years to determine links to specific diseases, said lead author Ellen Meara, an assistant professor of health-care policy at Harvard Medical School in Boston. The U.S. government and health groups may need to better target health programs at less-educated groups to reduce the disparity in life expectancy, the researchers said.

"If we really want to target the least advantaged, we really need to understand why all groups are not able to take advantage or enjoy the benefits of things that improve health,'' Meara said. "We tend to think of life expectancy as increasing. This is a wake-up call because it is not for everybody.''

The researchers reviewed death certificates and census population estimates for whites and blacks in the U.S. from 1981 through 1988 and 1990 through 2000.

In both time periods, life expectancy rose for people with more than 12 years of education, while remaining about the same for those with 12 years or less, the study found. From 1990 to 2000, the better-educated group had a life expectancy increase of 1.6 years compared with no increase among the less educated, the study found.

Smoking

Twenty-one percent of the mortality differences in the 1990s were attributed to lung cancer and chronic obstructive pulmonary disorder, conditions caused by smoking, the researchers said. People with less education tend to smoke more. Heart disease and cancer, excluding lung cancer, contributed to about 32 percent of the difference.

Those who are less educated also tend to have lower incomes and less access to health insurance and health care, Meara said.

"We like to think that as we as a country get healthier, everyone benefits,'' David Cutler, a study author and dean for social sciences at Harvard University, said in a statement distributed by the school. "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 was funded by the National Institutes of Health.