As many as 2 million American men already have osteoporosis, the bone thinning that makes bones brittle and porous and at likely to fracture. Twelve million men are at risk, and may have early signs of bone loss and low bone density, called osteopenia. But given that four times as many women have osteoporosis, men are less likely to end up with thin bones than women.
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"Women live longer, so they're more likely to get osteoporosis," says Paul Mystkowski, MD, an endocrinologist at Virginia Mason Medical Center in Seattle and clinical faculty member of the University of Washington in Seattle. And because men are generally more physically active over the course of their lives, he says, men are less likely to lose bone mass, since exercise has been shown to protect bone density.
But there's an even bigger difference with male osteoporosis.
"In general, osteoporosis in men is considered a symptom of something else," says Mystkowski, "whereas in older women, it's almost always postmenopausal."
And for many men, that "something" is hormonal.
Causes of Male Osteoporosis: Testosterone Deficiency
The most common cause of male osteoporosis is testosterone deficiency, says Mystkowski. "There's a clear consensus that when you're evaluating men with osteoporosis, you always evaluate for testosterone deficiency," he says.
For low-testosterone men, doctors may advise testosterone replacement to build bone mass. The dilemma is that science hasn't yet shown how much of the bone-building benefit is a direct testosterone effect -- or the result of turning testosterone into estrogen. "Probably the bulk of the benefit is the testosterone," Mystkowski says, "but it's important not to minimize the role of testosterone to estrogen conversion."
Men also need a small amount of estrogen, says Mystkowski. Estrogen preserves bone density -- in both men and women. In fact, all men normally convert testosterone to estrogen to build bone mass.
"If you look at men who lack an enzyme to make even small amounts of estrogen because they were genetically born that way," says Mystkowski, "they get osteoporosis. If you give them estrogen, their osteoporosis improves. So even though estrogen doesn't circulate in very high concentrations in men, it's a critical factor for bone health."