As the bones thin they become fragile, easy to fracture, and in certain circumstances a fracture can occur even with the slightest amount of trauma and even with normal movement. Osteoporosis is much more common in women than in men.
Estrogen deficiency causes the calcium to leak out or be absorbed from the bones.
Other factors which increase the risks of osteoporosis include early menopause, deficiencies of calcium, the lack of physical activity, certain drugs, smoking, and the use of alcohol. Each of these causes or risk factors can be reduced, and in most cases, it is much easier to prevent the problem than to try and treat the osteoporosis once it has become severe or after a fracture has occurred. The loss of sex hormones or 'estrogen' either by surgical removal of the ovaries or menopause will result in the subsequent loss of bone mass. Clearly, there is a balance between the risks of the drugs and the risks of osteoporosis. The major risk with hormone replacement is the possible increased risk of developing breast cancer or cancer of the uterus.