Temperature, Age, Gender, and Kidney Stones

Anyone who has passed a kidney stone will tell you that it is a very unpleasant experience, sometimes accompanied by pain so severe that one literally cannot remain still. We know that many types of kidney stones (e.g., uric acid, calcium oxalate, and struvite—a mineral made of magnesium, ammonium, and phosphate) relate in part to genetics, metabolism, and diet, but what about environmental influences? Going outdoors can make a person cold or warm, and sometimes dehydrated. What about age and gender?

Steven Pincus and his colleagues in Australia looked at these questions by performing a retrospective (after the fact) analysis of patients passing kidney stone (suffering renal colic) between 1999 and 2005 who presented to a Victoria (Australia) urban emergency department. They investigated the correlation between renal colic incidence and mean monthly temperature and humidity. In a publication entitled “The effects of temperature, age and sex on presentations of renal colic in Melbourne, Australia” (European Journal of Emergency Medicine 2010, 17:328-331), they concluded that the incidence of clinically apparent kidney stones increases with sustained increases in ambient temperature, and is not affected by age or gender. Because of the patterns they observed, they recommended that persons at risk for passing kidney stones should increase their fluid intake over the whole of the summer period and not just during periods of extreme heat.

This advice makes sense, given historical observations that persons who suffer kidney stones are prone to recurrences during periods of personal dehydration. In warmer weather, and particularly during times of exertion with pronounced sweating, when fluid losses are usually greater than during cooler weather, one needs to make a conscious effort to remain well hydrated. How effective such hydration would be to prevent the formation and passage of kidney stones is not proven, but it seems like a reasonable approach. Whether or not increased sun exposure during summer months causes production of increased levels of vitamin D and therefore also of calcium and oxalate excretion remains to be determined.

How much hydration is adequate to have a positive impact on persons with kidney stones? Although the volume of three liters of urine per day has been mentioned in the literature, it is probably wise to suggest that one drink enough liquid to maintain the urine at a light color—even to the point of being clear if possible. For persons in the outdoors, attention to urine color would be particularly important during exposure to cold, heat, and high altitude, when thirst alone may not be an adequate stimulus for ingesting sufficient liquids to avoid dehydration.