“If you don’t have hot flashes until you’ve stopped menses, then you won’t have them as long,” said Nancy Avis, a professor of social sciences and health policy at Wake Forest Baptist Medical Center and the study’s first author. “If you start later, it’s a shorter total duration and it’s shorter from the last period on.”

Hot flashes, which can seize women many times a day and night — slathering them in sweat, flushing their faces — are linked to drops in estrogen and appear to be regulated by the hypothalamus in the brain. Studies have found that women with hot flash symptoms also face increased risk of cardiovascular problems and bone loss.

Researchers followed the women in the study, who came from seven American cities, from 1996 to 2013. All of them met the researchers’ definition for having frequent symptoms: hot flashes or night sweats at least six days in the previous two weeks.

Image Mary Hairston found that acupuncture helped with her hot flashes. Credit... Karen Tam for The New York Times

None had had a hysterectomy or both ovaries removed, and none were on hormone therapy. (If they started taking hormone therapy during the study period, their data stopped being included, Dr. Avis said.)

Although some smaller studies have also found that symptoms can last many years, the new research drew praise from experts because, among other things, it included a larger and much more diverse group of women. One-third of them were African-Americans in Pittsburgh, Boston, Chicago and Ypsilanti, Mich. It also included women of Japanese descent in Los Angeles; women of Chinese descent in Oakland, Calif.; and Hispanic women in Newark — about 100 in each group.

“It’s such a real-world study of women we are seeing day in and day out,” said Dr. Risa Kagan, an obstetrician-gynecologist at the University of California, San Francisco, and the Sutter East Bay Medical Foundation in Berkeley. “There is no other study like this.”