DOCTOR'S VIEW ARCHIVE

Taking Calcium Supplements? Want To Avoid Kidney Stones?

A study published in the New England Journal of Medicine, April 1, 1997, has important implications for women who take calcium supplements for the prevention of osteoporosis, a common condition affecting 20 million women that results in thinning of bones and leads to fractures of the hips and spine.

Kidney stones also are a common condition in which stones form in the kidney and result in pain, bleeding into the urine, and blockage of the ureters, the tubes that conduct urine from the kidney to the bladder. The major components of the most common type of kidney stone are calcium and oxalate both of which come primarily from the diet, that is, the food we eat.

The study was a large, epidemiological study of 91,731 nurses who had never had kidney stones and were between the ages of 34 and 59 at the beginning of the study in 1980. The nurses were followed with questionnaires for 12 years. The questionnaires asked specifically about dietary habits, calcium supplements, and kidney stones. The dietary intake of calcium also was estimated from the dietary habits.

During the 12 years of the study, 864 nurses developed kidney stones for the first time. Each year, one of every 1,000 nurses developed stones (for an incidence of 0.1% per year). There was a strong association between higher dietary calcium intake and stones, that is, the greater the intake of calcium, the fewer the nurses developing stones. Nurses taking the highest amount of dietary calcium were half as likely to develop stones as women taking the lowest amount of dietary calcium.

Among nurses taking calcium supplements (in addition to their dietary calcium) the risk of developing stones was greater than among nurses not taking calcium supplements. Specifically, nurses taking supplemental calcium were 20% more likely to develop stones as women not taking supplemental calcium.