Women in 180 counties and men in 11 counties were living 1.3 fewer years by 1999 than in 1983, according to an analysis of mortality statistics and Census data published in tomorrow's Public Library of Science Medicine journal. The differences in death rates across the 2,068 large counties and groups of small counties studied also widened during this period.

Improvements in medical science added six to seven years to the average American's life since 1961, with men expected to live to age 74 and women to age 80 by the end of the last decade, the study found. The halt of this trend in certain areas beginning in 1983 is "troubling" and marks a "reversal of fortunes" for a minority of the population, the authors said.

"The study emphasizes how important it is to monitor health inequalities between different groups, in order to ensure that everyone -- and not just the well-off -- can experience gains in life expectancy," researchers from Harvard University's Initiative for Global Health wrote in the study.

The decline in life expectancy was caused by increased mortality from lung cancer, diabetes and chronic obstructive pulmonary disease, the study found. A rise in HIV/AIDS cases and homicide also contributed to higher death rates in men. The authors didn't name the counties where life expectancy fell.