Gearing up for a marathon race? Beware, the physical stress caused by running may cause kidney injury, researchers, led by one of Indian-origin, have warned.

In the study, 82 per cent of the runners had Stage 1 Acute Kidney Injury (AKI) soon after the race. AKI is a condition in which the kidneys fail to filter waste from the blood. The researchers stated that potential causes of the marathon-related kidney damage could be the sustained rise in core body temperature, dehydration or decreased blood flow to the kidneys that occurs during a marathon.

"The kidney responds to the physical stress of marathon running as if it's injured, in a way that's similar to what happens in hospitalised patients when the kidney is affected by medical and surgical complications," said Chirag Parikh, Professor at Yale University in Connecticut, US. Although kidneys of the examined runners fully recovered within two days post-marathon, the study raises questions about potential long-term impacts of this strenuous activity at a time when marathons are increasing in popularity, the researchers said in the paper published in the American Journal of Kidney Diseases.

Previous studies have shown there are also changes in heart function associated with marathon running. For the study, the team analysed participants who took part in the 2015 Hartford Marathon. The team collected blood and urine samples before and after the 26.2-mile or 42-km event. 

They analysed a variety of markers of kidney injury, including serum creatinine levels, kidney cells on microscopy and proteins in urine.