Bone loss and osteoporosis develop so slowly in most women whose bones test normal at age 65 that many can safely wait as long as 15 years before having a second bone density test, researchers report in a new study.

The study, published in Thursday’s issue of The New England Journal of Medicine, is part of a broad rethinking of how to diagnose and treat the potentially debilitating bone disease that can lead to broken hips and collapsing spines.

A class of drugs, bisphosphonates, which includes Fosamax, has been found to prevent fractures in people with osteoporosis. But medical experts no longer recommend the medicines to prevent osteoporosis itself. They no longer want women to take them indefinitely, and no longer consider bone density measurements the sole defining factor in deciding if a woman needs to be treated.

Now, with the new study, researchers are asking whether frequent bone density measurements even make sense for the majority of older women whose bone density is not near a danger zone on initial tests, recommended at age 65.