Calcium, Vitamin D Supplements Increase Kidney Stone Risk
New research finds that taking calcium and vitamin D supplements (1,000 mg and 400 IU, respectively) for seven years can increase the risk of kidney stones by 17 percent in postmenopausal women. But don’t be too quick to throw out your calcium and vitamin D supplements.
Calcium and vitamin D benefits outweigh risk
Subjects in the study included 36,282 postmenopausal women who were part of the Women’s Health Initiative (WHI). Under the direction of Robert Wallace, MS, MD, from the University of Iowa, researchers evaluated data from 18,176 women who took a calcium citrate/vitamin D supplement and 18,106 women who took a placebo for an average of seven years.
Overall, 449 women in the supplement group reported a kidney stone during the trial compared with 381 women in the placebo group. Kidney stones, also known as urinary tract stones, develop from crystals that separate from urine within the urinary tract. Although urine contains chemicals that inhibit the formation of crystals, these inhibitors do not always work.
The most common type of kidney stone contains calcium along with either phosphate or oxalate, all chemicals that are part of a normal diet as well as substances that make up bone and muscle. Men tend to get kidney stones more than women, for whom the prevalence of kidney stones peaks in their 50s.
Researchers in this study did not have any information concerning the chemical makeup of the kidney stones reported by the women, nor could they distinguish between the impact of calcium and vitamin D with respect to the development of stones. They also noted in the article that other previous studies have found a 17 to 20 percent increased risk of stone formation regardless of meals.
Other dietary factors in addition to vitamin D and calcium are associated with kidney stone formation, including fluids, animal protein, sodium, sucrose, and oxalates. Oxalate is of special interest because most stones contain calcium oxalate. Foods that contain oxalate include spinach, collards, almonds, peanuts, soybeans, berries, chocolate, black tea, and okra, among others.
The study’s authors concluded that their findings “have implications” for use of calcium and vitamin D supplements. Harry Rice, PhD, director of regulatory & scientific affairs for the United Natural Products Alliance, commented on the study, stressing that the findings should not change public health policy regarding supplementation with calcium and vitamin D, given previous research showing that the benefits of supplementation outweigh the risks.
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