Women in large swaths of America are dying younger than they were a generation ago, reversing nearly a century of progress in public health and underscoring the rising toll of smoking and record obesity.

Nationwide, life expectancy for American men and women has risen over the past two decades, and some U.S. communities still boast life expectancies as long as any in the world, according to newly released data. But over the past decade, the nation has experienced a widening gap between the most and least healthy places to live. In some parts of the United States, men and women are dying younger on average than their counterparts in nations such as Syria, Panama and Vietnam.

Baltimore remains among the areas with the lowest life expectancies, though improvements accelerated at twice the national average during the most recent decade studied.

Overall, America is falling further behind other industrialized nations, many of which have also made greater strides cutting child mortality and reducing preventable deaths.

In 737 U.S. counties, life expectancies for women actually declined between 1997 and 2007. For life expectancy to decline in a developed nation is rare. Setbacks on this scale have not been seen in the U.S. since the Spanish influenza epidemic of 1918, according to demographers.

"There are just lots of places where things are getting worse," said Dr. Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington, which conducted the research. "We're not keeping up."

The widening gulf between the healthiest and least healthy populations is partly due to wealth. But part of the gap appears to be attributable to cultural norms and differences in public health efforts, the researchers found.

Communities with large immigrant populations — Southern California, for example — fared considerably better than average despite relatively high poverty rates. The worst-performing counties were clustered primarily in Appalachia, the deep South and the lower Midwest. In those places, women died as much as a year younger in 2007 than women did a decade earlier. Life expectancy for women slipped 21/2 years in Madison County, Miss., which recorded the biggest regression.

A key finding of the data is that "inequality appears to be growing in the U.S.," said Eileen Crimmins, a gerontologist at the University of Southern California who also co-chaired the 2011 National Academies panel on life expectancies. "We are different than other countries." Researchers found substantially fewer geographic disparities in Great Britain, Canada and Japan, for example.

In general, men and women die youngest in poor, mostly rural parts of the South and in struggling urban centers like Philadelphia and St. Louis. In Baltimore, men on average live only 66.7 years.

By contrast, Americans in affluent counties near Washington, the San Francisco Bay Area and elsewhere have among the longest life expectancies in the world, outpacing even international leaders such as Japan and Switzerland.

The state and Baltimore's health officials have long recognized that those in the wealthier suburbs live longer and so do those in wealthier city neighborhoods.

For example, average life expectancy in Hollins Market is 20 years shorter than in wealthier Roland Park.

Dr. Oxiris Barbot, city health commissioner, said it amounts to a lot of "preventable death."

The city has adopted programs over the years to address the disparities, and Barbot recently unveiled a new program called Healthy Baltimore 2015 that seeks to involve most neighborhood, hospitals, businesses and faith organizations in the city. It sets specific goals for reducing the prevalence of Baltimore's most pervasive killers, such as HIV infection, heart disease and smoking.

"The fact that Baltimore City and cities like it continue to have shorter life expectancies than other areas draws attention to the fact that what we do in addressing the public health challenges has to go beyond the traditional health models," Barbot said. "We need to address the social determinants of health and adopt a health-in-all-policies approach."

That approach has already helped the statistics, said Frances B. Phillips, a deputy secretary of the state Department of Health and Mental Hygiene. The University of Washington report showed a jump in life expectancy of 4.1 years for men in Baltimore and 2.2 years for women in the decade ending in 2007 — about twice the national average.

Since then, Phillips said, the state's own data show that life expectancy for men and women in the state increased to 72.9 years in 2008-2009 from 72.4 years in 2006-2008.

She said the city and state have to continue focusing on access to health care, but also social and environmental factors, particularly in less affluent neighborhoods.

For now, she said, "Your ZIP code represents so many influences and opportunities you have to stay healthy or not."