Osteoporosis

A decrease in the rate of bone mineralization is a predictable effect of aging. For example, in infancy, the turnover rate of calcium in bone is 100%; by adulthood, this turnover rate falls to only 18% per year.

Women are particularly prone to osteoporosis because of several factors. Women have less bone mass than men to begin with, so the threshold level at which osteoporosis may cause fractures is reached more quickly. It is believed that the bone formation phase is encouraged in some way by the presence of estrogen. In women, estrogen production drops off drastically following menopause (the cessation of the menstrual period). This change in the chemical environment within the bodies of older women apparently results in a decrease in the bone formation phase. With bone resorption continuing at its normal pace, but without the normal pace of bone replacement occurring, bone mass decreases.

Because the pattern of bone formation occurs in response to weight/stresses borne by the bone, disuse osteoporosis occurs in individuals who are on bed rest for prolonged periods of time, as well as in individuals experiencing the relative weightlessness of space flight.

Other causes of osteoporosis include many diseases which alter the hormonal/chemical environment of the body, including thyroid disease, disease of the parathyroid (a gland responsible for calcium levels within the body), gastrointestinal diseases (which can alter the ability of the body to absorb calcium in the diet), diseases which decrease the amount of estrogen produced, and certain liver diseases.

Alcohol and some drugs can also affect calcium levels in the body, thus producing osteoporosis. Some of these drugs include thyroid medications, steroid preparations, anti-seizure medications, and certain chemotherapy (anti-cancer) agents.

Congenital diseases (diseases present at birth) of connective tissue (a group of tissues of the body which includes bone) can cause abnormalities of bone structure, and therefore osteoporosis. Such diseases include osteogenesis imperfecta (brittle bone disease) and Marfan syndrome.