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Osteoporosis is caused by a lack of bone strength or bone density.
As a natural part of aging, bone tissue breaks down. It is absorbed faster than new bone is made, and bones become thinner. You are more likely to have osteoporosis if you didn't reach your ideal bone density during your childhood and teen years.
Osteoporosis is much more common in women than in men. In women, bone loss increases around menopause. That's when ovaries decrease production of estrogen, a hormone that protects against bone loss. So the older a woman gets, the more likely she is to have osteoporosis.