Distance runners are well aware of the stress their chosen activity places on their leg muscles, cardiovascular system and joints. Less obvious is the toll that prolonged running can take on the gastrointestinal, or GI, tract, in particular the lower portion of it. GI bleeding -- either occult or obvious -- is common in distance runners, especially marathoners, and may either be rooted either in pre-existing conditions or a direct result of running itself.
Causes
During heavy exercise, blood is preferentially directed through the working muscles to meet these muscles' fuel and oxygen needs. As a result, blood flow to the intestines is reduced to just 20 to 50 percent of normal, according to a report by the American Medical Athletic Association, or AMAA. The resulting ischemia, or blood deprivation, can lead to damage and blood in the stool. Erosive esophagitis and mechanical damage to the viscera also contribute to GI bleeding during running.
Prevalence
According to the AMAA, the percentage of marathon runners who experience some level of GI bleeding as measured by post-race stool sampling ranges from 8 to 30 percent. The prevalence of bleeding is tied to the duration of running, as 83 percent of finishers of a 100-mile race demonstrated evidence of GI bleeding. Overall, adverse gastrointestinal symptoms of some sort -- such as nausea, vomiting blood, gastroesophageal reflux and ulcers -- occur in about one-third to two-thirds of long distance runners.
Effects
Blood loss results in a decrease in the oxygen-carrying capacity of the blood owing to direct deficits in hemoglobin, the component of red blood cells that binds to oxygen molecules. Hemoglobin synthesis is reliant on iron stores, and if these stores are diminished owing to GI bleeding as well as to typical losses in sweat and, in females, menstrual blood, then performance will ultimately suffer as frank anemia develops. In cases of iron deficiency, a physical may recommend oral iron supplements, but some people have trouble tolerating these.
Prevention and Treatment
If GI bleeding is sufficient to produce iron deficiency and attendant anemia, iron supplementation may be useful. Dietary modification can also be therapeutic; foods containing heme iron, such as red meats, provide a more easily absorbed form of the mineral than do grains and vegetables high in iron. A study published in "The British Journal of Sports Medicine" suggests that taking proton-pump inhibitors, such as omeprazole, can prevent GI bleeding in distance runners.
References
- "American Medical Athletic Association Journal"; Gastrointestinal Bleeding in Endurance Runners; Stephanie Horn and Edward R. Feller; Winter 2003
- Pediatric Education: How Common is Lower Gastrointestinal Bleeding in Athletes?
- "British Journal of Sports Medicine"; Proton Pump Inhibition Prevents Gastrointestinal Bleeding in Ultramarathon Runners: a Randomised, Double Blinded, Placebo Controlled Study; M. Thalmann et al.; April 2006
