While one in four women over the age of 50 has osteoporosis, only one in eight men has the disease. This striking difference is largely due to the important role which the sex hormones (primarily estrogen) play in keeping women's bones healthy.

Bone is a living tissue that is constantly renewed through a process in which old bone is removed and replaced by new bone. In Bone there are two important types of cells - Osteoblasts and Osteoclasts. Osteoclasts are bone eroding cells and Osteoblasts are bone forming cells. The bone eroding cells invade the bone and erode it creating cavities in the bone and the bone forming cells fill the cavities with new bone. This is a natural process — nature's way of restoring bones and keeping them strong.
In younger persons with good bone health, both the cells that erode bone and those that build bone work together. But as we age the bone builders are unable to keep pace with the bone excavators, and this results in loss of bone. Estrogen has been found to play a major role in maintaining the balance by slowing the pace of bone erosion.

Research has shown that when a woman's estrogen levels fall dramatically, bone loss is accelerated.
During Menopause, a woman's estrogen significantly decreases as her ovaries — where nearly all estrogen is produced — cease to function. A woman can lose 2 to 5 % of her bone density each year during the first 5 to 10 years following menopause. However, not all women develop osteoporosis despite this accelerated bone loss. For example, a woman who enters menopause with a high bone density will be less likely to develop osteoporosis because she has more bone to start with. Other factors are also important including genetics, physical activity and nutrition.

Early Menopause
The relationship between bone health and estrogen raises great concern in women who experience premature menopause — menopause before the age of 45. Sometimes such a menopause occurs naturally, while other times it is medically induced through surgery or chemotherapy. Whatever the cause, early menopause can lead to significant bone loss.

Amenorrhea (Missed Periods)
Amenorrhea is a condition which can develop when a girl or young woman develops an eating disorder or when she is training in sports or other intensive physical activities where she over-exercises. In such cases her menstrual cycle may be disrupted and her estrogen production will decrease.
Periods of estrogen loss during this time of life — even if temporary — can have a profound effect on a woman's bone health over her lifetime.
As a result, even if she does not develop osteoporosis early in life , she will reach menopause at a great disadvantage and be a likely candidate for postmenopausal osteoporosis.

Estrogen Halts Bone Loss
If used early enough this can prevent a woman's bones from becoming osteoporotic. In cases where she has low bone density or has already fractured, estrogen can stabilize or even improve her bone density.

Research has provided enough evidence to make a strong case for the use of estrogen as both a preventive therapy and as a treatment for established osteoporosis.