Obese older women who never took postmenopausal hormones are at almost double the risk of developing ovarian cancer compared to their normal weight peers, a new study finds.

Among all older women, however, obese women were only at slightly higher risk for ovarian cancer than those of normal weight, the scientists found.

Researchers at the National Cancer Institute looked at differences among women who had never used hormone replacement therapy because it may play a role in the development of cancer. The comparison helps to tease out the effects of other risk factors, the authors said.

The study is to be published in the Feb. 15 issue of the journal Cancer.

The findings add to an ongoing scientific controversy over the potential association between body weight and ovarian cancer. “We speculate that what may be driving the increased risk among the obese is the surplus estrogen produced by the fat cells in the body,” said Dr. Michael F. Leitzmann, a former investigator at the National Cancer Institute and first author of the paper.