Causes

Because the patterns of reforming and resorbing bone often vary from patient to patient, experts believe several different factors account for this problem. Important chemicals (such as estrogen, parathyroid hormone, and vitamin D) and blood factors that affect cell growth are involved with this process. Changes in levels of any of these factors could play a role in the development of osteoporosis.

The Role of Sex Hormones in Bone Breakdown

Although ordinarily associated with women, sex hormones play a role in osteoporosis in both genders, most likely by controlling the birth and duration of life of both osteoclasts (bone breakers) and osteoblasts (bone builders).

text continues below

Women and Estrogen. Experts are still puzzled by the rapid decline in bone density after menopause, when a woman’s ovaries stop producing estrogen. Estrogen comes in several forms:

The uterus is a hollow muscular organ located in the female pelvis between the bladder and rectum. The ovaries produce the eggs that travel through the fallopian tubes. Once the egg has left the ovary it can be fertilized and implant itself in the lining of the uterus. The main function of the uterus is to nourish the developing fetus prior to birth.

The most potent form of estrogen is estradiol. Estradiol deficiency appears to be a very strong factor in the development of osteoporosis.
The other important but less powerful estrogens are estrone and estriol.

The ovaries produce most of the estrogen in the body, but it can also be formed in other tissues, such as body fat, skin, and muscle. After menopause, some amounts of estrogen continue to be manufactured in the peripheral body fat. Even though the ovaries have stopped producing estrogens directly, they continue to be a source of the male hormone testosterone, which converts into estradiol.

Estrogen may have an impact on bone density in various ways:

Estrogen’s most important effect on osteoporosis appears to be prevention of bone breakdown (resorption). Some research suggests that estrogen may control the life span of osteoclasts, the cells responsible for bone breakdown.
One study reported that part of estrogen’s beneficial actions may involve maintaining normal levels of vitamin D, an important nutrient in bone protection.