Researchers followed more than 200,000 women for more than 25 years, recording data on lifestyle, health factors and disease outcomes and updating information with periodic interviews.

They found 1,054 cases of ovarian cancer. After adjusting for other variables, they found that women who took a baby aspirin — 100 milligrams or less — had a 23 percent reduced risk for ovarian cancer compared with those who did not. They found no risk reduction for those who took a standard 325-milligram pill.

“Our study has limits,” said the lead author, Mollie E. Barnard, a postdoctoral fellow at the Huntsman Cancer Institute at the University of Utah, “but we do have prospective data, and a very large sample followed over a long period of time. And we were able to look at standard and low-dose separately.”