Is it something in the dairy?
Several studies have pointed out that higher levels of dietary calcium may decrease kidney stone risk, but calcium supplements may increase risk. Most of these studies have looked at calcium from dairy products, since that's the most common source in Western populations.
To see what effect dietary calcium from all sources had on kidney stone risk, researchers from Harvard Medical School and Maine Medical Center pooled information from the Health Professionals Follow-Up Study and the Nurses' Health Study I and II that included results from 226,627 people. They determined how much calcium the people consumed in their diets from dairy and non-dairy sources and related that to their risk of developing calcium oxalate kidney stones.
Here's what they found:
Over the combined 56-year follow-up period, 5,270 cases of kidney stones were reported.
Compared with people who consumed the smallest amount of calcium (about 260 mg per day) from nondairy sources, risk of developing kidney stones was 29% lower in those who ate the most (about 450 mg per day).
In those who consumed the most calcium from dairy sources (about 860 mg per day) the chance of developing kidney stones was up to 24% lower, compared with those who ate the least (about 160 mg per day).
"Our current data enable us to dismiss the important possibility that dairy products were solely responsible for previously observed associations between higher dietary calcium and a lower risk of incident kidney stones," said lead study author, Eric Taylor, who speculated that the effect of supplemental calcium on kidney stone risk depends on whether calcium supplements are taken with or between meals. Taking calcium supplements with meals may not increase kidney stone risk.
Nondairy calcium sources
Don't tolerate dairy? Don't worry! Collards, sardines, kale, almonds, black-eyed peas, broccoli, sesame seeds, tofu, scallops, and Brazil nuts are all packed with calcium to help keep your kidneys healthy.
(J Urol 2013;doi:10.1016/j.juro2013.03.074)