Q: I am 65 years old and was advised never to take estrogen following surgery for breast cancer. I am concerned about osteoporosis and wonder whether it can be prevented by taking calcium supplements.
A: A recent editorial in the New England Journal of Medicine by Dr. Robert Heaney has clarified the confusing results of the many studies done to determine the effects of dietary calcium on the development of osteoporosis in postmenopausal women. Most, but not all, of these studies showed that calcium supplements slowed the loss of bone or reduced the number of fractures. However, some studies were flawed by a failure to control the amount of calcium women took.
Dr. Heaney showed that bone loss was slowed or stopped by calcium supplements in 16 of the 19 studies that did take into account the amount of added calcium. Moreover, a significant benefit of calcium was shown in all 12 studies that began at least five years after the menopause.
Other studies have shown a reduction in bone fractures when diets were supplemented with either vitamin D alone or a combination of calcium plus vitamin D. Derivatives of vitamin D, which are formed in the liver and kidney, promote the absorption of calcium from the intestine. Blood levels of these vitamin D derivatives tend to be low in older individuals.
Dr. Heaney concluded that it "seems prudent to increase the intake of calcium and vitamin D in most postmenopausal women -- calcium to at least 1,000 and preferably to 1,500 milligrams per day, and vitamin D to 400 to 800 IU daily."
Since dietary calcium intake in most postmenopausal women is less than 750 milligrams per day, a daily calcium supplement of about 1,000 milligrams would be needed to achieve a total intake of 1,500 milligrams or more of calcium.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for faculty affairs at the school.