Higher daily mean temperatures are associated with an increased incidence of kidney stones, according to researchers.

Gregory E. Tasian, MD, of the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, and colleagues estimated the relative risk of kidney stone presentation associated with mean daily temperatures using the MarketScan Commercial Claims database. The study included 60,433 patients who sought medical evaluation or treatment of kidney stones from 2005–2011 in Atlanta, Chicago, Dallas, Los Angeles, and Philadelphia.

As daily temperatures increased to more than 10° C (50° F), the risk of kidney stone presentation over the following 20 days also increased in most cities, the researchers reported in Environmental Health Perspectives (2014;122:1081-1087).

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Compared with a reference daily mean temperature of 10° C, a daily mean temperature of 30° C (86° F) was associated with a 38% increased cumulative relative risk of kidney stone presentation in Atlanta, a 37% increased risk in Chicago, a 36% increased risk in Dallas, an 11% increased risk in Los Angeles, and a 47% increased risk in Philadelphia, the study found.

The maximum of risk of kidney stone presentation occurs in 3 or few days following exposure to high temperature, according to the investigators.

“Our estimations suggest that there is a graded increase in the risk of patients seeking medical care for kidney stones as average daily temperatures increase and that the time between hot days and kidney stone presentation is short,” the authors wrote.

The link between high ambient temperature and kidney stone formation is thought to be dehydration, which results in urinary concentration and low urine volume and pH. “This increases the relative supersaturation of calcium and uric acid, which thereby promotes nucleation, growth, and aggregation of lithogenic minerals in urine,” the authors explained.