Chicago ? The chances of dying within a year after obesity surgery are much higher than previously thought, even among people in their 30s and 40s, a study of more than 16,000 Medicare patients found.

Some previous studies of people in their 30s to their 50s – the most common ages for obesity surgery – found death rates well under 1 percent. But among 35- to 44-year-olds in the Medicare study, more than 5 percent of men and nearly 3 percent of women were dead within a year, and slightly higher rates were seen in patients 45 to 54.

Among patients 65 to 74, nearly 13 percent of men and about 6 percent of women died. In patients 75 and older, half of the men and 40 percent of the women died.

The study involved 16,155 Medicare patients who underwent obesity surgery between 1997 and 2002. It was published in today’s Journal of the American Medical Assn.