LOS ANGELES — A significant rise in hip fractures among women is one result of the decade-long slide in the popularity of hormone replacement therapy, researchers report.

The landmark Women’s Health Initiative study showed that hormone therapy helps strengthen women’s bones and prevents fractures of hip, wrist and spine by 27 percent to 35 percent. However, hormone use fell out of favor after studies in 2002 showed it raised the risk of breast cancer and did not lower heart-disease risk and, in fact, may elevate the risk in some women. An estimated 93 percent of U.S. women quit using hormones and most stopped asking their doctors for new prescriptions.

While hormone therapy is clearly a trade-off, the benefits to bone health from taking hormones may have been lost on doctors and women over the last decade, said the authors of the new study, from the University of Southern California.

They looked at more than 80,000 women enrolled in Southern California Kaiser Permanente HMO plans and found that women who discontinued hormone therapy were at 55 percent greater risk of hip fracture compared with women who kept taking the medication. Hip fracture risk increased as early as two years after stopping hormones and the risk increased the longer women were off hormones.

The link was found even among women taking the bone-health medications called bisphosphonates.

Many questions about hormone therapy have been raised since the hormone-therapy boom went bust, such as whether certain groups of women may benefit from hormones despite the known risks. The authors of the new study stop short of saying that women should reconsider hormones, but they do warn doctors and women to think more seriously about bone health in the absence of hormone use.

About one-quarter of women who have a hip fracture die within one year. One-quarter require long-term care after a hip fracture and 50 percent suffer a long-term loss of mobility.

“With approximately 1 million women entering menopause each year in the United States alone, the health consequences of bone fracture may have potentially enormous survival and economic consequences if an effective prevention strategy is not in place,” they wrote.

The study is published in the journal Menopause.