Americans are living longer, but not in every corner of the country. A new study shows that in hundreds of U.S. counties — mostly in the South — life expectancy has fallen.

The researchers believe problems like smoking and obesity are partly to blame.

“There are enormous variations within the country” said Dr. Christopher Murray, a University of Washington researcher. He’s a study author and an editor of the online journal, Population Health Metrics, which released the study Wednesday.

Overall, life expectancy in the U.S. is at an all-time high. The Centers for Disease Control and Prevention recently estimated that a baby born in 2009 could expect to live 78 years and 2 months.

The CDC doesn’t calculate estimates by county; Murray’s research covers 2000 through 2007 when U.S. life expectancy grew a year to nearly 78.

A federal expert in these kinds of statistics said Murray’s methods were sound, but the findings aren’t terribly surprising.

The U.S. estimate actually dropped from 2004 to 2005, noted Bob Anderson of the CDC’s National Center for Health Statistics. Given that downward blip — and the fact that statistics fluctuate more when you’re dealing with smaller populations —— it’s not unexpected to see some declines at the local level, he said.

The study found that life expectancy for women fell significantly in 702 of the nation’s more than 3,100 counties. The largest declines — by nearly 2 years — were in Mississippi’s Madison County, near Jackson, and the adjacent Hughes and Okfuskee counties in eastern Oklahoma.

Life expectancy dropped for men in 251 counties, by more than 2 years in Kentucky’s Perry County in Appalachia and Mississippi’s Madison.

In 158 counties, it dropped for both men and women. In some cases, counties with plummeting life expectancy were next to or very near counties with rising longevity.

There is some debate about why life expectancy estimates rose and fell more in some counties than others.

Murray and his colleagues said they checked issues like poverty or racial makeup, and those didn’t explain the difference. They believe high rates of obesity, smoking and other preventable health problems may be main reasons.

Some experts disagree, saying the findings may be tied to the availability of good health care or with the migration of healthy people from one place to another.

Perhaps young blacks and whites are leaving to go off to college or work somewhere else. “That leaves the least educated and the least healthy” back in the original counties, Anderson said.

Or, in some places, the arrival of healthy Hispanic immigrants may be the reason, said Dr. Roger Rochat, an Emory University public health professor and trained demographer.

But Murray said his research finds migration theories are not the answer; there’s been little movement in or out of most places with the lowest life expectancy.

The counties with the largest increases in male life expectancy, though, were metro areas lush with jobs and universities — almost four years in Georgia’s Fulton County (Atlanta) and more than three years in New York City, Washington and nearby Alexandria, Va.

For women, the biggest jumps — 3 1/2 years — were in Alexandria and a Wyoming County that includes the affluent Jackson Hole.

Curiously, third on that list was Louisiana’s Orleans Parish even though it included the 2005 devastation of New Orleans by Hurricane Katrina. A large number of healthy women could have stayed in the city or returned the next two years, Rochat said.

“I think it’s a change in who’s living there,” he said.

Online:

http://www.pophealthmetrics.com/