TUESDAY, March 11 (HealthDay News) -- Life expectancy in the United States is on the increase, but only among people with more than 12 years of education, a new study finds.

In fact, those with more than 12 years of education -- more than a high school diploma -- can expect to live to 82; for those with 12 or fewer years of education, life expectancy is 75.

"If you look in recent decades, you will find that life expectancy has been increasing, which is good, but when you split this out by better-educated groups, the life expectancy gained is really occurring much more so in the better-educated groups," said lead researcher Ellen R. Meara, an assistant professor of health care policy at Harvard Medical School.

"The puzzle is why we have been successful in extending life span for some groups. Why haven't we been successful in getting that for less advantaged groups?" Meara said.

The answer may lie with tobacco, the study found.

About one-fifth of the difference in mortality between well-educated and less-educated groups can be accounted for by smoking-related diseases such as lung cancer and emphysema, Meara said.

But the disparity in life expectancy is not only a function of education, Meara said. "Those with less education are likely to have lower income. They're likely to live in areas that have their own health threats, either through crime or poor housing conditions. In addition, they may have worse access to health insurance coverage and health services," she said.

The study was published in the March/April issue of Health Affairs.

For the study, Meara's team collected data on people who took part in the National Longitudinal Mortality Study. The researchers used death certificates, plus estimates from Census data, to create two datasets -- one covering 1981 to 1988 and the other from 1990 to 2000.

The researchers found that in both datasets, life expectancy rose but only for people with more than 12 years of education. For those with 12 years of education or less, life expectancy remained flat through the periods.

When the researchers compared data from the 1980s to data from the 1990s, people with more education had almost a year and half of increased life expectancy. But, for people with less education, life expectancy increased by only six months.

In the period of 1990 to 2000, the better educated saw their life expectancy increase by 1.6 years. For the less educated, life expectancy didn't increase in all.

When the researchers looked at gender differences, they found that less-educated women actually had a decline in life expectancy. In 2000, those women with more than 12 years of education by age 25 could expect to live five years longer than less-educated women, the study found.

The challenge, Meara said, is to figure out ways to extend life expectancy of all groups in U.S society. "We need to get a better understanding of how we can extend these great things we're learning about how to lead healthier lives into these groups," she said.

Dr. David L. Katz, director of the Yale University School of Medicine's Prevention Research Center, thinks fighting poverty and improving education are key to increasing life expectancy among less-advantaged Americans.

"Disparities in health are a major challenge in the United States," he said. "The less affluent and less educated are also, invariably, less healthy."

Initiatives that target health disparities are always welcome, but they may not go far enough if they don't relieve underlying discrepancies in educational or economic status, Katz said.

"Despite efforts throughout the 1980s and 1990s to reduce the disproportionate mortality and morbidity burden experienced by ethnic minorities and the socio-economically disadvantaged, those burdens have persisted," Katz said. "And the gap in life expectancy between the more educated and the less has actually widened."

The take-home message is to redouble efforts to eliminate health disparities, Katz said. "Health is not a product of health care per se, but of one's life course and opportunities. Poverty and limited education are enemies to both opportunity and health. Public health efforts must strive against them as earnestly as against the diseases they drag in their wake."

In another report in the same journal issue, Rachel Kimbro, a sociology professor at Rice University, and colleagues found that immigrants with low levels of education fared better in health outcomes compared with native-born Americans, regardless of race or ethnicity.

The researchers said these differences should be taken into account when targeting programs to reach specific groups of people.

More information

For more on health-care disparities, visit the U.S. Agency for Healthcare Research and Quality.