TUESDAY, Dec. 18 (HealthDay News) -- One bone mineral density test can accurately predict a woman's chance of spinal fractures 15 years down the line, new research shows.

And, according to the largest and longest prospective study of osteoporosis ever, women who had a spinal fracture at the beginning of the study had four times the risk of sustaining another fracture later on.

The bottom line: "Women need to talk to their doctors about the risk of osteoporosis," according to Jane Cauley, lead author of the study and professor of epidemiology at the University of Pittsburgh Graduate School of Public Health.

Her team published the findings in the Dec. 19 issue of the Journal of the American Medical Association.

"I agree with the guidelines that all women after the age of 65 have bone density tests, and Medicare will pay for that," Cauley said. "Women who are postmenopausal, 50 to 64 years of age, should consider having a bone density test if they have other risk factors for osteoporosis or if they want to know what their bone density is before they consider any other treatment."

The findings don't change current standard practice, experts said, and they don't change the basic message to women: Don't ignore bone health, especially in middle and old age.

"The only really major advance here is that it's a longer term study. Mostly studies are five years typically. This one went out 15 years," said Paul Brandt, associate professor of neuroscience and experimental therapeutics at Texas A&M Health Science Center College of Medicine in College Station. "Women need to get their bone mineral density tested after they start menopause and if they stay on hormone replacement therapy or an anti-osteoporotic treatment." he said.

Postmenopausal women are particularly vulnerable to fractures resulting from osteoporosis, a degenerative weakening of the bones. Some 10 million Americans, including one in five American women over the age of 50, suffer from osteoporosis, which is the most common type of bone disease.

Spinal fractures are the most common type of fracture resulting from osteoporosis, affecting 35 percent to 50 percent of women over 50 (about 700,000 vertebral fractures annually in the United States).

But many, if not most, of these fractures go undetected. "Osteoporosis is sometimes called the silent thief," Cauley said. "It basically robs the skeleton of strength and resources, and women don't really know about it. About 75 percent of all spine fractures actually occur silently."

"Identifying risk factors for spine fractures is less well developed. You have to systematically look for them by repeated X-rays," Cauley continued.

The findings from this study are based on bone mineral density data from 2,300 women over the age of 65 who enrolled in the Study of Osteoporotic Fractures (SOF), initiated in 1986.

After 15 years of follow-up, it was evident that 25 percent of women who had low BMD at the beginning of the study developed fractures of the spine, compared with only 9 percent of women with normal BMD.

"It was pretty much a strong gradient of risk," Cauley explained. "If you had normal bone density when you entered and did not have an [existing] fracture, the risk of having a new spine fracture was about 9 percent, compared to a risk of 56 percent in women who had osteoporosis and who had an existing fracture. So, the range of risk varied dramatically depending on bone density and previous spine fractures."

According to Brandt, one interesting finding from the study is that a previous vertebral fracture topped even bone mineral density as a predictor for future fracture.

This indicates that women with an existing vertebral fracture should be treated for osteoporosis regardless of their BMD, the authors reported.

"People think osteoporosis is an inevitable consequence of aging, but it is preventable and treatable," she said.

More information

There's more on age-linked bone loss at the U.S. National Library of Medicine.