WASHINGTON (AP) — Women's life expectancy declined significantly in 180 U.S. counties, mostly in the deep South and Appalachia, between 1983 and 1999, according to a study being released Tuesday.

Researchers blamed the decrease in women's life expectancy on high blood pressure as well as chronic diseases related to smoking and obesity, such as lung cancer and diabetes.

The decline, averaging 1.3 years in the 180 counties. Men's life expectancy declined by 1.3 years in only 11 counties.

In another 783 counties, women's life expectancy declined by 0.5 years, but the researchers said those results were not statistically significant because those counties were relatively small.

The study, based on data from the National Center for Health Statistics and the U.S. Census Bureau, was designed to analyze disparities in life expectancy between different counties with different social conditions and health programs.

Overall, life expectancy rose for both men and women between 1961 and 1999. For men, it increased from 66.9 years to 74.1 years; for women, it rose from 73.5 years to 79.6 years.

Between 1961 and 1983, no counties had a statistically significant increase in mortality, the study said, noting that the reduction for both sexes was caused by a reduction in cardiovascular mortality.

From 1983 on, however, "The worst-off counties no longer experienced a fall in death rates, and in a substantial number of counties, mortality actually increased, especially for women," the researchers wrote. Life expectancy of women in those counties was 75.5 years in 1999.

"The study emphasizes how important it is to monitor health inequalities between different groups," the researchers wrote, "in order to ensure that everyone — and not just the well-off — can experience gains in life expectancy."

The analysis was conducted by researchers at Harvard University, the University of California, San Francisco, and the University of Washington. It was posted Monday night in the online journal PLoS Medicine, a publication of the Public Library of Science, an organization of scientists and physicians.

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PLoS Medicine: http://medicine.plosjournals.org/