During childhood and teen years, new bone grows faster than existing bone is absorbed by the body. After age 30, this process begins to reverse. As a natural part of aging, bone dissolves and is absorbed faster than new bone is made, and bones become thinner. You are more likely to have osteoporosis if you did not reach your ideal bone thickness (bone mineral density) during your childhood and teenage years.

In women, bone loss increases around menopause, when ovaries decrease production of estrogen, a hormone that protects against bone loss. Likewise, testosterone protects men from bone loss. Osteoporosis is typically seen in men older than 65, when production of this hormone declines. In both men and women, the older you get the more likely you are to have osteoporosis. See an illustration of healthy bone versus bone weakened by osteoporosis.

Not getting enough calcium, vitamin D, and phosphorus contributes to bone thinning. In addition, a tendency for lower bone mass may pass from parent to child.