(Reuters Health) -- An increase in heat waves worldwide linked to climate change may be behind epidemics of kidney disease detected in workers who are increasingly exposed to heat and dehydration, according to a research review.
Global warming has increased temperatures overall by nearly 1 degree Celsius (just under 2 degrees Fahrenheit) over the past century, and they are expected to rise by another 3 to 4 degrees C by the end of this century, the authors write. Heat waves have also become more common, with about three quarters of the increase blamed on climate change, they add.
"There's evidence that long periods of heat waves have increased more significantly with climate change, when it's extremely hot the risk for kidney damage begins to really become evident," said senior study author Dr. Richard Johnson of the University of Colorado, Denver.
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Extreme heat exposure can have immediate health effects, causing dehydration, heat exhaustion and heat stroke, as well as worsening pre-existing chronic disease, which can be fatal, Johnson and his colleagues write in the Clinical Journal of the American Society of Nephrology.
Although chronic kidney disease is often caused by diabetes or high blood pressure, it can also be the result of recurrent heat exposure with physical activity and not enough hydration, which puts a heavy strain on the kidneys.
Chronic kidney disease often has no symptoms and has to be diagnosed by blood test. In early stages it may be treated with medications, but as kidneys fail over time they may require dialysis to filter the blood, and ultimately they can fail entirely, leading to death or kidney transplant.
Johnson and his coauthors studied reports of upticks in cases of chronic kidney disease detected in hot climates and among populations without regular access to healthcare, such as poor agricultural workers.
A recent epidemic of chronic kidney disease in Central America, particularly among male sugarcane workers on the Pacific coast, was initially suspected to be linked to chemicals or other toxins, for example. But the kidney damage was found to be more common among sugarcane cutters than among pesticide applicators, and less common at higher altitudes where temperatures are cooler - suggesting that workers with the greatest exertion and heat exposure had the highest risk.
A similar epidemic is currently affecting about 100,000 individuals in northern Sri Lanka, primarily among young to middle-aged male rice farmers and women working in the fields, the authors write. Still another epidemic is affecting Andhra Pradesh on the southwestern coast of India, an area with some of the longest heat waves in the country.
Heat waves occur when sustained temperatures reach 40 degrees C (104 degrees F), or the temperature increases by 5 to 6 degrees C over the normal maximum temperature of the region or any time temperatures reach 45 degrees C (113 degrees F) or greater.
"It is undeniable that there will be numerous direct and indirect health effects as a result of climate change," said Rebecca Laws, a postdoctoral associate at Boston University School of Public Health who was not part of the new study. "We could be witnessing one such direct health effect, as epidemics of (chronic kidney disease) become more apparent in hot and humid regions throughout the world," she said.
"To better understand potential implications from climate change, we need to conduct more research to determine the role of heat stress and dehydration in each geographic region, as well as identify the underlying biological mechanisms," Laws told Reuters Health by email.
Similar epidemics may be ongoing in the hotter regions of Africa and the Middle East, and improving hydration and worksite practices may help prevent some heat related cases of chronic kidney disease, the authors write. But more studies are needed to determine whether there is a cause and effect relationship at work.
"There's enough here to warrant concern that heat stress and dehydration could be a real problem for poor people working in the field," Johnson told Reuters Health.
"I think improving hydration and providing shade can be recommended now," he said. "Will it prevent this epidemic? That needs to be tested."
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