Climate change ‘will cause increase in kidney stones’

As the world warms due to climate change, more of us will suffer from kidney stones due to hot temperatures and dehydration, research has shown.

Kidney stones could increase by up to 3.9% in US states such as Carolina, scientists at the Children's Hospital Of Philadelphia found.

Researchers used two different climate change scenarios to estimate the effects of global warming on kidney stone disease in Carolina.

Gregory E Tasian, an attending paediatric urologist in the Division of Urology at the hospital, said: "With climate change, we don't often talk about the impact on human health, particularly when it comes to children, but a warming planet will have significant effects on human health.

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"While it is impossible to predict with certainty how future policies will slow or hasten greenhouse gas emission and anthropogenic climate change, and to know exactly what future daily temperatures will be, our analysis suggests that a warming planet will likely cause an increased burden of kidney stone disease on healthcare systems."

Kidney stone disease is a painful condition caused by hard deposits of minerals that develop in concentrated urine and cause pain when passing through the urinary tract.

The incidence of the condition has increased in the last 20 years. Prior research demonstrated that high ambient temperatures increased the risk of developing kidney stone disease.

In the US, there is an increase in the incidence of kidney stones from north to south, and there is a rapid increase in risk of kidney stone presentations following hot days.

However, previous studies have not precisely projected how climate change will impact the burden of kidney stone disease in the future.

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The researchers first worked out the relationship between historic daily temperatures and kidney stones in South Carolina from 1997 to 2014.

They used wet-bulb temperatures (WBT), a moist heat metric that accounts for both ambient heat and humidity, which is a more accurate temperature metric for predicting kidney stones. WBT refers to temperatures taken with a thermometer covered in a wet cloth, which are normally slightly cooler than ‘dry-bulb’ temperatures.

Researchers then used that data to forecast the heat-related number of kidney stones and associated costs to 2089, based on projected daily WBT under two climate change scenarios.

The first scenario represents an 'intermediate' future, with shifts to lower-emissions sources of energy, the use of carbon capture technology, prices on CO2 emissions, and an expansion of forest lands from the present day to 2100.

The second scenario represents a future with mostly uninhibited greenhouse gas emissions.

Using their model, the researchers found that by 2089, kidney stones due to heat would increase statewide by 2.2% from baseline in the ‘intermediate’ future and by 3.9% in a more pessimistic projection.

In the near future, WBT could be crucial for determining which areas of our warming planet remain habitable.

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Human beings can survive very high temperatures (well over 50C) when humidity is low, but in high humidity humans cannot survive temperatures of even 35C for long periods, because there is no way to cool down by sweating.

Even the fittest people often die within hours in such conditions.

WBT allow researchers to work out whether humans can sweat: if the water evaporates, the thermometer cools down, so that 'wet bulb' temperatures are lower than 'dry bulb' temperatures.

In high humidity, the water will not evaporate, and WBT will be the same as the dry-bulb temperature.

Previously, WBT of 35C or higher were thought impossible, but last year scientists reported that places in the Persian Gulf had reached the threshold.

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