By Maggie Fox

WASHINGTON (Reuters) - Life expectancy may have reached an all-time high for the United States, but it is declining in many poor counties, especially among women, researchers reported on Monday.

Smoking, obesity and high blood pressure are taking the lives of women in Appalachia, Mississippi River states and parts of Texas, a team at Harvard School of Public Health reported.

"There has been increasing disparity in health in the U.S. population for two decades," said Majid Ezzati of the school's department of population and international health, who led the study.

"The people who are worst off are either not getting better or are worse off" than they had been, Ezzati added in a telephone interview.

Last September, the U.S. Centers for Disease Control and Prevention reported that U.S. life expectancy had risen to almost 78 years in 2005 -- up from 75.8 years in 1995 and 69.6 years in 1955. The United States ranks around 42nd in the world in life expectancy.

The CDC noted that U.S. whites will live longer than blacks, and women longer than men. But Ezzati found many exceptions to this rule.

"Female mortality increased in a large number of counties, primarily because of chronic diseases related to smoking, overweight and obesity, and high blood pressure," the researchers wrote in the Public Library of Science journal PLoS Medicine.

Ezzati and colleagues analyzed death rates in all counties of the U.S. states from 1961 to 1999.

INCHING BACK UP

Overall U.S. life expectancy increased mostly because of fewer deaths from heart disease, the No. 1 cause of death, and stroke. But by the 1980s, death rates started to head back up in many counties.

"The majority of these counties were in the Deep South, along the Mississippi River, and in Appalachia, extending into the southern portion of the Midwest and into Texas," Ezzati's team wrote.

"The rise in all-cause mortality was caused by an increase in cancers, diabetes, COPD (chronic obstructive pulmonary disease, mostly emphysema), and a reduction in the rate of decline of cardiovascular diseases," they wrote.

"There was also an important influence of HIV/AIDS and homicide among men."

Ezzati said the worst-affected counties had other troubles, such as lower levels of educational achievement.

"One of the questions we are asking is whether our ranking in the world is getting increasingly worse because we are not doing a good job of taking care of the worst-off," Ezzati said.

"To have 20 years of decline for about one out of five American women, it is something that is rather unprecedented," he added. "We are leaving a larger and larger part of the population behind."

While many of the worst-affected counties had a high black population, Ezzati found that white populations in poorer counties fared worse that whites elsewhere, too.

"It exists above and beyond race," he said.

"Life expectancy decline is something that has traditionally been considered a sign that the health and social systems have failed, as has been the case in parts of Africa and Eastern Europe," said Christopher Murray of the University of Washington, who worked on the study.

"The fact that is happening to a large number of Americans should be a sign that the U.S. health system needs serious rethinking."

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