Coffee v. Kidney Stones
Scientists have confirmed an association between coffee and a reduced risk of kidney stones. Examining the effects of liquids on kidney stone development, they found varying impacts among different liquids. Integrating results from three large clinical trials, their analysis showed that some sodas and punch appeared to increase the risk, while coffee and wine reduced it.
The coffee effect appears to increase with consumption. Participants who drank one or more cups of coffee a day had a 26% lower risk of developing kidney stones, as compared with those who drank coffee less than once a week. The protection was incremental, with relative risk reduction increasing with consumption levels: 3% for those who consumed coffee once a week, 6% for those who drank two to four times a week, and 16% for five to six times a week.
The effect remained steady for decaffeinated coffee as well. Decaf drinkers who consumed one or more cups of coffee per day showed a 16% lower risk compared with those who drank it less than once a week. While risk levels were higher by 3% for those who drank decaf just once a week, reductions were significant for other consumption levels: 8% for two to four times a week, and 23% for five to six times a week. Although caffeine is known to reduce kidney stone risk, the decaf results suggest that there are independent sources within coffee that contribute to the risk reduction.
For comparison, red and white wine also appears to deliver significant protection, culminating with a 31% reduction in daily consumers for red wine and 33% for white. Beer and liquor also exhibited protection levels for daily consumption at 41% and 12%, respectively, although protection levels for less frequent consumption did not increase incrementally with levels. Sugar-sweetened colas and non-colas did not fare as well, with daily consumption yielding respective 23% and 33% risk increases. Artificially sweetened colas and non-colas did better, with a risk reduction in colas of 9% albeit only for daily consumption, and for non-colas risk changes ranging from a 2% reduction to a 17% increase, depending on frequency. The researchers point to the fructose in the sugared beverages as the possible cause of the increased risk levels.
The study was conducted by Drs. Pietro Manuel Ferraro, Eric N. Taylor, Giovanni Gambaro and Gary C. Curhan. Subjects totaled 194,095 followed over a period of time ranging from eight to 13 years. That puts the combined reach of the study, integrating subjects and time followed, at 2,643,708 person-years. The study was published on May 15 in the Clinical Journal of the American Society of Nephrology (CJASN).