Increased intake of dietary calcium may help protect younger women from developing kidney stones. The use of calcium supplements, however, has no effect on the risk. An inverse association between dietary calcium and kidney stone risk has been noted in older women and men, but studies have not adequately addressed this relationship in younger women. Researchers from the Harvard Medical School in Boston conducted a study and analysed data from more than 96,000 young women who participated in the Nurses' Health Study II, a study spanning several years. The women completed dietary questionnaires in the early 1990s and were followed until a kidney stone was diagnosed, death occurred, or May 31, 1999--whichever came first. During follow-up, 1,223 symptomatic kidney stones were diagnosed. Women with the highest levels of dietary calcium intake were 27 percent less likely to develop stones than those with the lowest levels. Dietary levels of phytate, a salt that contains magnesium and calcium, was also tied to a decreased risk of stone formation. The risk reduction between women with the highest and the lowest levels of phytate intake was even higher than that seen with dietary calcium--37%. The consumption of animal protein and fluid was associated with a reduced risk, while sugar intake seemed to raise the risk. In older adults, there has been evidence that supplemental calcium can raise the risk of stones, but no such effect was seen in the current group of younger women. The findings reinforce the idea that routine restriction of dietary calcium in patients who have had a kidney stone is no longer justified. Also dietary phytate may be a new, important, and safe addition to our options for stone prevention.
Archives of Internal Medicine,
April 2004