NEW YORK - 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 today’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, 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 they no longer consider bone density measurements to be the single 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 close to a danger zone on an initial test.
“Bone density testing has been oversold,’’ said Steven Cummings, the study’s principal investigator and an emeritus professor of medical epidemiology and biostatistics at the University of California, San Francisco.
The study followed nearly 5,000 women aged 67 and older for more than a decade. The women had a bone density test when they entered the study and did not have osteoporosis. (In a separate national study by the Centers for Disease Control and Prevention, about 70 percent of women over age 65 did not have osteoporosis.)
The researchers report that less than 1 percent of women who have normal bone density when they entered the study and less than 5 percent with mildly low bone density developed osteoporosis in the ensuing 15 years. But of those with substantially low bone density at the study’s start, close to the cut-off point for osteoporosis of less than 2.5 standard deviations from the reference level, 10 percent progressed to osteoporosis in about a year.
Dr. Margaret Gourlay, the study’s lead author, and a family practice specialist at the University of North Carolina, said she and her colleagues were surprised by how slowly women progressed to osteoporosis.
Medicare pays for a bone density test every two years, and many doctors have assumed that this is the ideal interval, although national guidelines say only that screening should be done at “regular intervals.’’