Older women whose diets include too little calcium or water - or too much salt - have an increased risk of developing kidney stones, a study confirms.
Researchers found that among more than 78,000 U.S. women in their 50s and 70s, the risk of developing first-time kidney stones declined as calcium or fluid intake climbed. On the other hand, the odds went up with a higher sodium intake.
Kidney stones develop when the urine contains more crystal-forming substances -- like calcium, uric acid and a compound called oxalate -- than can be diluted by the available fluid.
People prone to developing kidney stones have long been told to increase their water intake; fluid helps dilute the chemicals that can lead to stones. Cutting down on salt can help because too much sodium increases calcium levels in the urine.
Since most kidney stones contain calcium, it was once thought reducing calcium intake could help.
But studies in recent years have suggested that dairy foods, rich in calcium, may actually be protective. These latest findings, reported in the Journal of Urology, confirm these recent findings.
Doctors have been concerned about the calcium question in older women, since they are at increased risk of thinning bones and fractures.
The study from the University of Washington School of Medicine in Seattle involved 78,293 U.S. women who were followed for an average of eight years. During that time, 2.5 percent, one in 40, were diagnosed with kidney stones for the first time.
Among the women who ate the most calcium at the outset, the odds of developing kidney stones was 28 percent lower, versus the women who got the least calcium. On average, women were eating about 800 milligrams of calcium per day.
Similarly, the group who drank the most fluid had a 20-percent lower risk of kidney stones than women with lowest intakes. Average water intake was about one and a half liters per day.
More sodium meant a higher risk. The women who consumed the most sodium were 61 percent more likely to develop stones than those with the lowest sodium intake.
Some of the biggest sources of sodium include fast food, processed meats and canned foods. People prone to kidney stones need to read labels on packaged foods and be careful when eating out.
People also need to be aware that cutting out dairy foods may actually contribute to kidney stones.
Calcium supplements are different, however. It may be because they provide a large, isolated dose of the mineral. People prone to stones should be "cautious" about calcium supplements the researchers said. But if a woman is on calcium to protect her bones, she should talk to her doctor about whether she can stick with it.
For women who need to take a calcium supplement, it’s recommended to take it with a meal. Doing so may help mitigate any effect of the calcium on stone formation.
Women older than 50 need to get 1,200 milligrams of calcium per day. In reality, few do. Of women in this study, for instance, 80 percent got less than the recommended amount of calcium.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.