Medical Research: What are the main findings of the study?
Dr. Ferraro: We analyzed the association between caffeine intake and the risk of developing kidney stones in three large cohorts of U.S. health professionals. The 217,883 participants included did not have any history of kidney stones when follow-up began. During 20 years of follow-up, 4,982 of them developed a kidney stone. In all three cohorts, participants with higher intakes of caffeine had a reduced risk of developing kidney stones. Intake of caffeine from sources other than coffee was also associated with reduced risk of kidney stones. Among 6,033 participants with 24-hour urine data, intake of caffeine was associated with higher excretion of calcium but also higher urine volume and lower likelihood of calcium and uric acid stone formation.
Medical Research: What was most surprising about the results?
Dr. Ferraro: Previous reports showed that caffeine could increase urinary excretion of calcium and oxalate, which would increase the risk of forming kidney stones, but higher caffeine intake makes the urine more dilute, which would lower the risk. Our study suggests that the overall effect of caffeine is to lower the risk.
Medical Research: What should clinicians and patients take away from your report?
Dr. Ferraro: There is now substantial evidence that higher caffeine intake is associated with a lower risk of kidney stones so patients who have had a kidney stone may not need to avoid caffeine.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Ferraro: Future research should investigate whether the effect of caffeine intake on stone risk varies by type of kidney stone.
Caffeine intake and the risk of kidney stones
Pietro Manuel Ferraro, Eric N Taylor, Giovanni Gambaro, and Gary C Curha
Am J Clin Nutr 2014 ajcn.089987; First published online October 1, 2014. doi:10.3945/ajcn.114.089987