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Calcium for the prevention of osteoporosis: The good and the not so good

It is often recommended to postmenopausal women that they increase their intake of calcium and Vitamin D to prevent the onset of osteoporosis, a disease characterized as mineralization of bone more than two standard deviations below normal. Women are especially prone to osteoporosis due to hormonal changes that occur during menopause and thereafter, specifically as the result of a lack of estrogen. The premise behind increasing calcium and Vitamin D intake is to ultimately result in an increased blood calcium level.

Increased calcium in the blood inhibits the secretion of a hormone called parathyroid hormone. Parathyroid hormone increases blood calcium levels in the body in several ways. Most important to this discussion, however, is the fact that it stimulates demineralization of the bone so calcium is freed from the bone and can be absorbed into the blood. Thus it is believed that by inhibiting the secretion of the parathyroid hormone into the blood, bone demineralization can be thwarted.

Though this seems logical, it is also known that as one ages, calcium starts building up in blood vessels and results in hardening and less elastic arteries; this can lead to increased blood pressure and general decrease in cardiovascular health. Increases in blood calcium may accelerate this hardening.

It was the query of a recent study to evaluate whether an increased cardiovascular risk occurs in women who take calcium to prevent osteoporosis. Unfortunately, an increased cardiovascular risk was observed and begs the question of whether the benefits of calcium and Vitamin D supplementation as a means to prevent osteoporosis outweighs the possible risks of accelerated cardiovascular disease.

Although conclusions can hardly be made with one or even a few such studies, the vast implications of these studies must make us reconsider if status quo recommendations are indeed of any merit and furthermore, if women are aware of this possible association.

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