Let’s talk about bone health.

Tom was cleaning out his attic 12 years ago when he tripped and hurt his ankle. An X-ray ruled out a fracture but revealed something unexpected: a severe bone loss that suggested osteoporosis, a condition in which the bones become thin and fragile. “The doctor said not to worry, just to take calcium supplements,” said Tom, a 57-year-old professor who did not want to give his full name or location.

Tom did worry, and a year later he had a bone density test, the definitive diagnostic exam for osteoporosis. It confirmed that he had the disease. But back then, there was nothing he could do to treat it, said Dr. Sarah L. Morgan, Tom’s present doctor and the medical director of the Osteoporosis Prevention and Treatment Clinic at the University of Alabama at Birmingham. There were no medications approved for men and no research on osteoporosis in men.

An enormous gender gap exists regarding information about osteoporosis. “With other conditions, like heart disease, women have gotten the short end of the stick, but the exception is osteoporosis,” said Dr. Donald A. Bergman, clinical professor of medicine at Mount Sinai School of Medicine in Manhattan and president-elect of the American College of Endocrinology.

Osteoporosis has long been considered a women’s disease because 80 percent of those affected are women. But in the last 5 to 10 years research has shown that osteoporosis also takes a significant toll on men. Two million men in the United States have the disease, and one in four will have an osteoporosis-related fracture in his lifetime. Such fractures are a major cause of disability in both men and women, but they are more likely to be fatal in men.

Osteoporosis is known as a silent disease because it usually causes no symptoms until bone fractures, most often in the spine, hip or wrist. Even when men find out they have it, many question the diagnosis. “The biggest challenge for men is believing that they have a ‘women’s’ disease,” said Dr. Deborah T. Gold, associate professor of medical sociology at Duke University Medical Center in Durham, N.C.

Men and women share many of the same risk factors. Not getting enough calcium and Vitamin D raises the risk because these nutrients help prevent bone loss. A lack of weight-bearing exercises may also increase the odds because these activities appear to increase bone density.

Additional shared risk factors are smoking; heavy drinking; a family history of osteoporosis; light skin; small bones; use of corticosteroid medications for more than three months; and several illnesses, including kidney or liver disease.

But other risk factors affect only men. Hypogonadism, or a low testosterone level, leads to bone loss. Testosterone helps guard against osteoporosis in men because some of it is converted to estrogen, a hormone that helps maintain bone density. Another risk factor is androgen ablation therapy for prostate cancer, which causes testosterone to drop.

Age increases the odds of developing osteoporosis in men and women, although they increase more slowly for men, perhaps because of a higher peak bone mass or because they have no sudden hormonal shift like menopause.

Perhaps the biggest obstacle in preventing and detecting the disease equally for both sexes is the lack of guidelines on screening men. The National Osteoporosis Foundation has recommendations for bone density testing in women but not for men. Dr. Bess Dawson-Hughes, president of the foundation, said there was not enough research to determine which men should be screened.

Other groups recommend that men, as well as women, have a bone density test after age 65, or earlier if they have additional risk factors like using corticosteroids for more than three months or having an unexplained fracture.

Some controversy exists over the screening results in men because their interpretation is based on comparisons among women, Dr. Dawson-Hughes said.

One question is whether men and women with the same bone density have the same fracture risk. “Some data are convincing that they do and others are convincing that they don’t,” Dr. Dawson-Hughes said.

She expects the answer in another year or so with the completion of “Mr. Os,” a seven-year study supported by the National Institutes of Health that is following 5,700 men aged 65 and older to clarify which osteoporosis risk factors are most important in men.

Meanwhile, the National Osteoporosis Foundation recommends that men take 1,000 milligrams a day of calcium for those under 50, and 1,200 milligrams a day for those over 50; 400 to 800 international units of Vitamin D a day for all men; doing weight-bearing exercises regularly; avoiding smoking, and restricting alcoholic drinks to about two a day.

Men with osteoporosis or low bone mass and other risk factors should talk with their doctors about taking medication to prevent more bone loss and reduce the risk of fractures.

Two of the five types of osteoporosis drugs are approved for men: bisphosphonates, like alendronate (Fosamax) and risedronate (Actonel), are taken orally; and parathyroid hormone, a bone-building hormone approved for men who are at high risk for fractures, is given by injection. Calcitonin, a hormone that inhibits bone reabsorption, is sometimes prescribed for men, although it is approved only for women and has not been tested in men.

Tom started taking Fosamax when it first came on the market, about 10 years ago. It upset his stomach, a common side effect, but “that was a small price to pay, given the alternative,” he said. His bone mass has remained stable, and he has not had a fracture.

Read more by Susan Gilbert, New York Times