Although adult mortality rates are lower in the US than they are in other developed countries, the geographic location of where people die most frequently in the US has shifted over time and is now concentrated in the central southern part of the nation, according to a new study from a Brown University researcher that suggests smoking may have a role in the mortality shift.

Between 1965 and 2004, the distribution of the US states with the highest levels of adult mortality changed dramatically. In 1965 the highest mortality rates were in Alaska, Rhode Island, Delaware, Pennsylvania and New Hampshire. But by 2004 there was a marked shift in mortality rates to south central states that were geographically contiguous - Alabama, Kentucky, Mississippi, and Tennessee.

Brown University's Andrew Fenelon, who is affiliated with the Population Council - a group that conducts biomedical, social science, and public health research - compiled data pertaining to the cause of death in each of these states.

For the purposes of his research he considered a death by lung cancer to be indicative of cigarette smoking.

"In the US, more than 90 percent of lung cancer deaths among men and more than 80 percent among women result from smoking," the Population Council said in a statement. "Although the prevalence of smoking declined in all states in that time period, southern states, particularly Kentucky, have maintained overall high levels of smoking."

From the five decades of data, Fenelon observed that mortality attributable to smoking peaked later in in the Central South. The death rate in the region was also significantly higher, which Felelon suggests is a indication of a greater and more persistent burden of smoking.

"By 2004, the gap in mortality attributable to smoking between the Central Southern states and states in other regions was exceptionally large: among men, smoking explained as much as 75 percent of the difference between the Central South and other US regions," the Population Council stated.

Tobacco laws in the South are generally more lenient than they are elsewhere in the country. There are 10 states that have no statewide smoking bans in places such a workplaces or restaurants. Nearly all of these states are in the south.

Relatively high smoking-attributable mortality in the South explains 50-100 percent of the divergence for men between 1965 and 1985 and up to 50 percent for women between 1985 and 2004. There is also a geographic correspondence between the contribution of smoking and other factors, suggesting that smoking may be one piece of a more complex health-related puzzle. State taxes on tobacco products are also lower in the South when compared to other states with lower mortality from smoking. Separate research has suggested that smoking bans and higher taxes reduce the prevalence of smoking.

"This study highlights geographic inequalities in health and mortality within the US and underscores the importance of narrowing these gaps as a public policy goal," the Population Council said.

Felenon's research is published in the journal Population and Development Review.