In a study conducted six years ago, Michigan's William Beaumont Hospital found that about 40 per cent of runners suffered acute kidney injury after marathons.
In a new study, nephrologist Chirag Parikh, a professor of medicine at Yale, elaborated on the relationship between marathon running and kidney injury.
In the American Journal of Kidney Diseases, Parikh writes that the rate of acute kidney injury was likely to be closer to 75 per cent. ''We demonstrated that there is the same amount of injury and inflammation after marathon running that we see in patients coming out of cardiac surgery or in the ICU,'' he told CNN.
However, he said the effect on our kidneys was not necessarily a bad thing.
The kidneys in our body filter our blood and vent the waste into our bladders. The waste contains the compound creatinine, a metabolic byproduct that could be taken as a fair indicator the state of our kidney function.
Healthy kidneys filtered creatinine from our blood easily, but when they were not being able to do a good job of it, the amount increased.
Parikh subjected runners in Connecticut's, Hartford Marathon to a battery of tests. Parikh and his team took blood and urine samples before and after the race, and also measured proteins in the urine that signalled inflammation (NGAL and interleukins).
They found that the degree of physical stress on the kidneys amounted to a five- to 10-fold increase from normal.
However, according to Parikh this could be a temporary effect and the kidneys largely repaired themselves in a few days.
According to experts, the findings needed to be replicated in larger follow-up research, but some runners - including those with kidney disease, diabetes, hypertension; those taking anti-inflammatory medications; and those older in age - should be mindful of the way long-distance running might affect the kidneys.
"It's possible that marathon running could be an acute stress and may contribute to the progression of existing chronic kidney disease, and this is where runners with this condition need to talk to their physicians and talk to their trainers," The Atlantic reported quoting Parikh.