Any marathoner will tell you that the gruelling 42-kilometer races can do a number of things to the hips, knees, ankles and feet.
Now, a small study suggests that these tests of endurance are also tough on the kidneys.
"Marathon runners demonstrate transient or reverse short-term kidney injury," said Dr Chirag Parikh, professor of medicine at Yale University.
Many have kidney injuries
In his study of 22 participants in the 2015 Hartford, Connecticut Marathon, Parikh found that 82% showed acute kidney injury after the race. In this condition, the kidneys fail to filter waste from the blood.
The good news is that the kidney injury seems to clear up within two days of the race, he said. "On day 2, they are all fine," Parikh said.
Parikh isn't certain why the strenuous event is linked with kidney injury. But some potential causes include the sustained rise in core body temperature, dehydration, or the decreased blood flow to the kidneys that occurs during a marathon, he explained.
Advice from an expert
It is however not all bad news
as the Heart and Stroke Foundation of South Africa recommends exercise
as a treatment for people with coronary artery disease because it helps
to rehabilitate the heart by restoring normal or near normal function of
the heart and lungs.
Well-known South African runner, Elana Meyer,
a former Olympic 10 000m silver medallist has the following advice for
marathon runners: "You need to be strong if you want to run a good
marathon. By incorporating strength conditioning it will help you stay
injury free and handle the distance a lot better. Also incorporate hill
repeats. It will make you tough."
When the blood is pumped to the skin and muscles while running, Parikh said, the kidneys may not get as much blood as they normally do.
To evaluate this type of kidney injury, his team looked at blood and urine samples collected before and after the marathon. These tests included measuring blood creatinine levels and proteins in the urine, along with looking at kidney cells through a microscope. Creatinine is a waste product excreted by the kidneys; measuring it in the blood helps assess kidney health.
Risks of chronic kidney disease
"The larger question looming is: do these repeated bouts of injury in endurance athletes lead to chronic kidney disease years later? Can anything be done about the injury at the time including hydration strategy?" McCullough said. More study is crucial, he added.
Parikh said additional research is also needed to assess whether certain people may not recover as quickly. For now, those with a family history of kidney disease should let their physician know they run marathons, he suggested.
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