David Feeny of Portland's Kaiser Permanente Center for Health Research said he confirmed the results of a 2005 study of U.S. residents that also found slightly overweight people live far longer than dramatically thin or obese individuals, The (Portland) Oregonian said Wednesday.
But Feeny warned the results of his study and its 2005 predecessor should not prompt people to attempt to gain weight to increase their lifespan.
The current standard for being overweight is a body mass index between 25 and 30, while a normal weight is considered to be between 18.5 and 25.
While a study focused on Canadian adults found similar results regarding weight and lifespan, The Oregonian said the reason for the correlation remains a mystery to researchers.
"The evidence is accumulating that overweight may be protective," Feeny said. "We need to understand why that might be the case and historically that wasn't."