Saturday science subject: Weight and life expectancy

Could being overweight make you live longer? That's essentially the conclusion reached by a research group from the Centers for Disease Control and Prevention and the National Cancer Institute. The New York Times says the group found that overweight people—those with a body mass index between 25 and 30—were less likely to die from diseases like Alzheimer's, Parkinson's, and lung disease than people who are obese or of normal weight.

Curiouser yet, the group found that overweight people are not likelier to die from other diseases like cancer, diabetes, or heart disease than those of normal weight. "As a consequence . . . there were more than 100,000 fewer deaths among the overweight in 2004, the most recent year for which data were available, than would have expected if those people had been of normal weight," the group found.

The numbers have led some, including Dr. Elizabeth Barrett-Connor from the University of California, to assert that a BMI between 25 and 30 "may be optimal." However, those people are missing the big picture, according to Dr. JoAnn Manson from Boston's Brigham and Women’s Hospital. Manson says overall health has to do with more than just mortality rates, citing other studies (including ones from Harvard) that say overweight people are likelier to suffer from diabetes, heart disease, and some types of cancer.

The researchers behind this latest study, too, warn that their data "cannot speak to cause and effect." They "do not yet know, precisely, what it is about being underweight, for instance, that increases the death rate from everything except heart disease and cancer." Nonetheless, Dr. Mitchell Gail, one of the researchers behind the study, advises that "if you are in the pink and feeling well and getting a good amount of exercise and if your doctor is very happy with your lab values and other test results, then I am not sure there is any urgency to change your weight."

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