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Hematuria – or blood in the urine occurs with some runners, and it is common. In one study, 18% of marathon runners had blood in their urine.

The general theory of why runners have blood in their urine is trauma. That is, foot strike causes mechanical destruction of red blood cells. However, new evidence has clouded whether this is the whole reason or more likely, part of the cause of hematuria.

In general, exercise induced destruction of red blood cells seems more prevalent and occurs to a greater extent with runners, but it has been seen with many activities—including non-traumatic activities such as swimming and cycling.

As a result, mechanical trauma is not the only factor in the destruction of red blood cells in athletes. Red blood cell fragility can be the result of dehydration, electrolyte changes, lactic acidosis and free radicals that  are released during exercise.

Another cause of sport related hematuria is repeated impact of the bladder wall against the bladder sac. In one case, the problem resolved when the runner with the problem stopped emptying her bladder prior to running.

Sport Related Hematuria May Be Beneficial

Some researchers believe hematuria in athletes is NOT a problem, but the body responding to the athlete’s need for more iron and protein.

This finding was boosted by a study by Shiraki et al that showed increasing the protein intake in the athlete’s diet caused the hematuria to disappear. Shiraki states that red blood cells are breaking down to give athletes the iron and protein that they need during endurance activities. Robinson (2005) also questions if hematuria is even pathologic.

What About the Pee of Barefoot Runners?

Intuitively, one would think barefoot running would be worse for your red blood cells. That is, the increased trauma of a barefoot hitting the ground would, in theory, mean more red blood cells destroyed, which in turn means more blood in your pee. However, one study compared protein in the urine of barefoot and shod runners and found no difference.

Interestingly, when the researchers measured the hemoglobin in the blood, the hemoglobin concentration of barefoot runners was higher.

Final Thoughts on Blood in the Urine of Athletes

The cause of blood in the urine could be due to a serious underlying medical problem, such as kidney, blood or prostate abnormalities. Thus, you must see a doctor for a blood test to make sure nothing serious is occurring.


Siegel AJ, Hennekens CH, Solomon HS, Boeckel B van. Exercise-related hematuria. Findings in a group of marathon runners. J Am Med Assoc 1979; 241: 391–392

Shiraki K, Yamada T, Yoshimura H.  Relation of protein nutrition to the reduction of red blood cells induced by physical training. Jpn J Physiol. 1977;27(4):413-21.

Robinson Y, Cristancho E, Böning D Intravascular hemolysis and mean red blood cell age in athletes.. Med Sci Sports Exerc. 2006 Mar;38(3):480-3.

Shaskey DJ, Green  Sports haematology. GA.Sports Med. 2000 Jan;29(1):27-38. Review.

Miller BJ, Pate RR, Burgess W. Foot impact force and intravascular hemolysis during distance running. Int J Sports Med. 1988 Feb;9(1):56-60.

Telford RD, Sly GJ, Hahn AG, Cunningham RB, Bryant C, Smith JA. Footstrike is the major cause of hemolysis during running. J Appl Physiol. 2003 Jan;94(1):38-42. Epub 2002 Aug 9.

Image Creditimage of human feet in sportshoes running down grass Photos by Pond5

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  • Barefoot-J

    Very informative article! Thank you