Researchers review causes of osteoporosis

Besides aging and calcium deficiency, what causes osteoporosis? A pair of physicians associated with the Institut National de la Sante et de la Recherche Medicale Unite in Paris recently laid out the known intrinsic and external causes of osteoporosis.

Their medical review, which appears in the Journal of Clinical Endocrinology and Metabolism, begins by noting that the aging process is one of the biggest determinants of the onset of osteoporosis.

In a series of diagrams depicting bone formation on the cellular level, the team illustrates the process of healthy bone creation and resorption. Bone tissue is shown being broken down by osteoclasts, which are specialized cells that remove bone minerals. In their wake, complementary cells called osteoblasts build the bone tissue back up again.

In young bones, this process appears balanced, in that bone levels stay relatively stable over time. However, the illustrations depict older bone formation as being increasingly dominated by osteoclasts, which slowly decrease bone mineral levels.

The authors state that several bodily health factors contribute to this process. Estrogen deficiency is a major accelerator of osteoporosis in postmenopausal women and elderly men, for example. Researchers state that while the average rate of bone loss in middle age is about 1 percent each year, once women begin to experience menopause, that figure increases to 5 or 10 percent per year.

Likewise, reduced physical activity can speed the onset of osteoporosis. The pair writes that as individuals age and engage in less exercise, the lack of mechanical force applied to the skeleton discourages osteoblasts from replacing bone.

Studies by scientists at the National Aeronautics and Space Administration have shown that a similar lack of activity results in the atrophy of muscle and bone tissue in astronauts on extended space missions.

The review's authors also point to vitamin D and calcium deficiencies, alcohol use, smoking and long-term glucocorticoid use as factors that boost the risk of osteoporosis.

An estimated 10 million Americans currently have osteoporosis, according to the National Osteoporosis Foundation.