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Diet Can Alter Risk of Kidney Stones

Calcium, whole grains and veggies are good choices

MONDAY, Nov. 17, 2003 (HealthDayNews) -- Belying the common belief that calcium contributes to kidney stones, a new study of young women has found eating foods rich in this mineral may actually reduce the risk of getting the painful condition.

Dietary calcium, whole grains and vegetables all appear to lower the chances you'll get kidney stones, while a high sugar intake may do the opposite, the study finds.

Contrary to what was believed in the past, eating more protein doesn't increase your risk of kidney stones either, the researchers say. The study also found no additional risk from taking calcium supplements.

"Dietary factors are important," says study author Dr. Gary Curhan, an associate professor of medicine and a nephrologist at Brigham and Women's Hospital in Boston. "Dietary modification may reduce an individual's risk of kidney stones. Our findings challenge the belief that calcium should be restricted."

Curhan presented the findings Nov. 16 at the American Society of Nephrology's annual meeting in San Diego.

Curhan and his colleagues gathered data from the large Nurses' Health Study II, which includes more than 100,000 women. For this study, the researchers focused on 96,000 women between the ages of 27 and 44 at the start of the study who had completed dietary information surveys in 1991 and 1995.

At the start of the study, none of the women had kidney stones. At the end of the eight-year study period, 1,223 women had developed kidney stones.

Kidney stones form from substances in the urine. The most common type of stone forms from calcium oxalate in the urine. Other substances that contribute to stone formation include uric acid, struvite and cystine, the researchers say.

Stones come in varying sizes -- from a grain of sand to the size of a golf ball. Some stones pass through the urinary tract system on their own, but some get stuck and block the flow of urine. When this happens, medical intervention is necessary.

The researchers found women who had the highest dietary calcium intake from foods such as milk, cheese and yogurt reduced their risk of kidney stones by 27 percent. Consumption of phytate, a naturally occurring substance found in whole grains and vegetables, lowered the risk of kidney stones by 37 percent, and a higher fluid intake also appeared to reduce the risk of kidney stones.

What did raise the risk of developing kidney stones was sugar. Sugar increased kidney stone risk in young women by slightly more than 30 percent. Meat and calcium supplements didn't appear to significantly increase or decrease the risk.

Dr. Khalid Zafar, a nephrologist at William Beaumont Hospital in Royal Oak, Mich, says, "The take-home message here is that people with kidney stones should not decrease dietary calcium and they can take supplements and eat meat."

He says the finding that supplements don't increase the risk of kidney stones in young women is especially important, because women need calcium to prevent osteoporosis, and many don't get sufficient amounts from their diet.

More information

To learn more about kidney stones, visit the National Institute of Diabetes and Digestive and Kidney Diseases.

SOURCES: Gary Curhan, M.D., associate professor, medicine, and nephrologist, Brigham and Women's Hospital, Boston; Khalid Zafar, M.D., William Beaumont Hospital, Royal Oak, Mich.; Nov. 16, 2003, presentation, American Society of Nephrology annual meeting, San Diego
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