Primary Osteoporosis - What Causes Osteoporosis: Osteoporosis

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Primary osteoporosis

The result of a normal physiological process, such as menopause or aging, primary osteoporosis is the most common form of the disease.

Type 1 primary osteoporosis

Type 1 primary osteoporosis, also known as postmenopausal osteoporosis, is the result of a rapid loss of bone associated with the decline in estrogen levels in women during the three to five years preceding menopause, at menopause, and following menopause. Typically, bone loss accelerates in the first few years after menopause, and then begins to level off. The effects are most prominent in the trabecular bone, which isn't as dense as compact bone. Several factors may contribute to this process. A number of researchers are examining the roles of chemical regulators, such as interleukin-1, interleukin-6, prostaglandin E2, and tumor necrosis factor, which appear to speed up bone resorption by spurring on osteoclasts as estrogen levels decline.

Type 2 primary osteoporosis

This condition results from the cumulative effects of the gradual loss of both trabecular and compact bone that occurs with aging. Type 2 primary osteoporosis develops more slowly than type 1 and is usually not apparent until age 75 or later. As with all age-related changes, it is probably due to several factors.

One is the general slowdown in bone formation as you age (see "Peak bone mass"). Another is a decline in the availability of minerals. With age, the intestines gradually absorb less calcium from the diet, and the kidneys seem to be less efficient at conserving calcium. Thus, more calcium is lost in the stool and urine, and less reaches the bloodstream, making it more likely that the bones' calcium stores will be tapped.

To make matters worse, most people consume less dietary calcium as they age, further straining the bones' calcium supplies. Many people shy away from dairy products, often because of lactose intolerance (the reduced ability to digest milk sugar), which can produce gas and abdominal discomfort. Others may shun calcium-containing foods and supplements because they have constipating effects.

The body's production of vitamin D frequently drops as well. Your skin cells use sunlight to produce a precursor of vitamin D; the liver and kidneys then convert this precursor into active vitamin D. Vitamin D plays a central role in the body's absorption of calcium and in the process of turning calcium into bone. If you don't have enough vitamin D to signal your intestines to absorb calcium, your body will break down bone to get the calcium it needs — no matter how much calcium you're getting from food or supplements. Many people don't get enough vitamin D — a problem that is particularly common among older adults. One reason is that people often spend less time in the sunlight as they grow older; thus, they are unable to produce an adequate supply of vitamin D. In addition, many older adults consume fewer vitamin D–fortified dairy products.

Last updated:	January 23, 2007