Gastrointestinal bleeding in endurance runners – GI

Stephanie Horn


Athletes participating in intense physical activity, especially long-distance running, commonly have a low hemoglobin and hematocrit. This “sports anemia” has been attributed to a physiologic response to exercise due to expansion of plasma volume that dilutes red blood cells. However, stool samples taken after intense workouts or post-race have revealed occult bleeding in 7-30% of marathoners with occasional reports of major upper GI or lower GI hemorrhage also reported in runners.

Exercise may decrease visceral blood flow to 20-50% of baseline, increasing risk of ischemic damage to stomach and intestine. Aerobic activity also decreases lower esophageal sphincter pressure, increasing risk of erosive esophagitis. Trauma of running may produce bleeding from hemorrhoids or anal fissures. Direct trauma to viscera may also cause injury.

GI blood loss or iron deficiency anemia in runners is multifactorial. In selected individuals, treatment may include dietary changes, acid-supressing medication, and avoidance of potentially injurious drugs. Since GI bleeding due to running is a diagnosis of exclusion, caution is needed in attributing blood loss to running-related causes without considering underlying digestive tract pathology.

Keywords: GI bleeding, anemia, running complications, mesenteric ischemia


Intense aerobic activity, especially long-distance running, is associated frequently with a low hemoglobin concentration. This “sports anemia” is a common physiologic response to exercise. As the body adapts to the loss of plasma volume with each endurance workout, salt and water are conserved. The result is an expansion of plasma volume proportionately greater than the increased erythropoiesis; thus, a normal number of red blood cells (RBC) is diluted, lowering the hemoglobin concentration and creating a dilutional pseudoanemia (1). However, anemia in athletes maybe secondary to multiple other mechanisms, including intravascular hemolysis from trauma to RBC’s, dietary iron deficiency, impaired iron absorption, hematuria, and gastrointestinal bleeding. Blood loss into the gut is important because of its potential effect on health and performance. Clinicians must be aware of the pathogenesis, prevalence, and diverse clinical manifestations of GI bleeding in runners. Further, before attributing anemia to the af orementioned etiologies, it is vital to assess the possibility of underlying organic disease of the GI tract, including, but not limited to, ulcers and tumors.

Causes of GI Bleeding in Runners

Intense physical activity may decrease splanchnic blood flow to 20-50% of baseline as blood is shunted to skin and exercising muscle(2). This response, which may be attenuated by training, is potentiated by high ambient temperature, dehydration and hypovolemia. Multiple endoscopic studies demonstrating ischemic colitis or gastritis support this mechanism as a source of blood loss in athletes with bleeding after prolonged endurance exercise (3). investigated seven runners with occult fecal blood loss after a marathon. In studies performed within 48 hours of the event, three had ischemic colitis, and two had gastric erosions typical of ischemia. In this series, pre-event endoscopies were normal and repeat studies done after a period of detraining revealed return to normal mucosa in these cases in which abnormal endoscopies had been observed after intense exercise. Isolated cases of mesenteric infarction have been reported after endurance exercise. Aerobic exercise also decreases lower esophageal sphincter press ure, potentiating reflux esophagitis as another possible source of bleeding. Physical activity may also produce rectal chafing, resulting in bleeding from hemorrhoids or rectal fissures. Other mechanisms observed include direct trauma to viscera from running on hard or uneven surfaces or mucosal damage from non- steroidal anti-inflammatory medication. Runners commonly complain of cramps or diarrhea with exercise. Athletes with bleeding may experience more frequent GI symptoms such as abdominal cramps or bloating than those who do not report bleeding(4). These complaints may reflect relative gut ischemia due to shunting of blood away from viscera during exercise.

Endurance Exercise and Iron Status

Regular exercise is associated commonly with a reduction in iron stores, but iron deficiency anemia is uncommon. Young women have particularly high physiologic iron requirements. Studies in adolescent female cross-country runners have revealed that serum iron and serum ferritin decrease frequently as conditioning progresses(5). Reports indicate a correlation between intensity of exercise training and iron status(6). Progressive decrease in serum ferritin measured in successive years has been demonstrated in competitive runners, swimmers, and field hockey players. Dramatic decreases in bone marrow hemosiderin levels have been reported in some distance runners. Clinicians must always be wary of the possible occurrence of nutritional iron deficiency, with caloric deficits common in sports emphasizing leanness (eg., running, gymnastics, and sport equivalents such as ballet dancing). A careful dietary history is mandatory. Whereas vegetables and grains provide good sources of non-heme iron, only 2-5% of non-heme i ron is absorbed, compared to 10-35% of heme iron derived from meats. A recent Institute of Medicine panel recommended increasing the daily dietary allowance of iron for women from 15 mg/day to 18 mg/day. Evidence indicates that very minor contributions to iron deficiency are attributable to a decrease in exercise-related erythropoiesis, sweat loss, hematuria, or impaired iron absorption.

Prevalence of Bleeding in Runners

GI blood loss is a common, usually occult occurrence in runners. Several research groups have reported occult bleeding in marathon runners, using pre-and post-race stool guaiac testing with the prevalence of blood in post-race specimens ranging from 8 to 30%(7). Baska and co-workers(8) found that after a 100-mile ultramarathon 83% of runners had guaiac positive stools, supporting the contention that intensity and duration of exercise correlate with blood loss. More sensitive quantitative tests using fecal hemoglobin concentrations of runners found average fecal values of 0.99mg/g before the race and 3.96mg/g after the race(3). Twenty-one of 24 runners had increased fecal hemoglobin in post-race samples compared to pre-race levels. Clinicians must assess intensity of exercise when evaluating possible exercise-induced blood loss. One study comparing marathon runners with walkers (37km/day for four days) demonstrated an increase in fecal hemoglobin of 0.42 to 0.87mg/g of stool in runners, while walkers were occu lt blood negative (9).

Effect of Iron Stores on Performance

Iron deficiency severe enough to produce anemia decreases maximum oxygen consumption and diminishes exercise capacity(6). Earlier studies suggested that iron deficiency without anemia did not have adverse effects on aerobic capacity. In one representative study of 40 female long-distance runners with mild iron deficiency, iron supplementation for two months did not improve exercise performance despite normalization of mean serum ferritin levels(5). A recent trial, however, found that iron supplementation can improve endurance after training in iron-deficient but nonanemic women(10). Iron deficiency without anemia may impair muscle oxidative capacity; thus, low serum iron or ferritin levels in the absence of anemia may diminish performance. Athletes with low serum ferritin levels may benefit from iron therapy directed by a health professional, both to prevent iron deficiency and to help normalize intestinal absorption of potentially toxic trace metals(eg., lead and cadmium)(11). However, the widespread use of iron supplementation without documented iron deficiency or anemia is unwarranted and potentially hazardous. Oral iron supplements have frequent side effects including nausea; crampy abdominal pain; constipation; potential interference with the absorption of copper, zinc, and certain antibiotics; and controversial increased risk of cancer, stroke, or coronary artery disease(12).

Practical Implications

Iron deficiency or digestive bleeding after exercise is multifactorial as noted. Intensity and duration of physical activity correlate with the presence of occult or macroscopic bleeding. In selected individuals, treatment may include dietary changes, change in training intensity or duration, or avoidance of training on hard surfaces. Athletes, especially those participating in endurance exercise, must minimize dehydration, ensure adequate nutritional intake, and use caution with medications that may predispose to bleeding (including anti-inflammatory drugs and oral contraceptives). Prostaglandins may be involved in the physiologic response to exercise; some data suggests a lower risk of bleeding in runners taking non-steroidal anti-inflammatory drugs (NSAIDS). Acid-supressing medications (histamine antagonists, proton-pump inhibitors) may prevent upper GI mucosal bleeding, but because there have been no large, well-controlled clinical trials of these interventions, recommendations must be limited. All recrea tional and competitive athletes should be questioned by treating health professionals concerning non-specific symptoms potentially due to anemia, including fatigue, weakness, dizziness, or unexplained decline in performance. Caution is needed in attributing blood loss or iron deficiency to exercise-related causes without considering underlying organic disease of the GI tract requiring diagnostic evaluation.

Table: Sports Anemia-Etiologies




* PSEUDOANEMIA (plasma volume expansion)


1. Occult

2. Hematemesis

3. Hematochezia

4. Melena





1. Direct trauma to red blood cells (RBC)

2. Hyperthermia decreases RBC survival




(1.) Elchner ER: Sports anemia, iron supplements and blood doping. Med Sci Sports Exerc 1992; 24(Suppl 9): S315-318.

(2.) Qatnar MJ, Read AB: Effects of exercise on mesenteric blood flow in man. Gut 1987; 28: 583-7

(3.) Schwartz AE, Vanagunas A, Kamel PI: Endoscopy to evaluate gastrointestinal bleeding in marathon runners. Ann Int Med 1990; 113: 632-633.

(4.) Schwartz AE, Vanagunas A, Kamel PI: The etiology of gastrointestinal bleeding in runners. A prospective endoscopic appraisal. Gastroint Endosc 1989; 35:194-7.

(5.) Nickerson HJ, htolubets M, Tripp: Decreased iron stores in high school female runners. Am J Dis Child 1985; 139: 1115-9.

(6.) Cook JD: The effect of endurance training on iron metabolism. Semin Hematol 1994; 31:146-154.

(7.) Mechrefe A, Wexler B, Feller ER: Sports anemia and gastrointestinal bleeding in endurance athletes. Med Health/RI 1997; 80: 216-8.

(8.) Baska RS, Moses FM, Graeber G, Kearney G: Gastrointestinal bleeding during an ultramarathon. Dig Dis Sci 1990; 35: 276-9.

(9.) Robertson J, Maughan R, Davidson R: Faecal blood loss in response to exercise. Brit Med J 1987; 295:303-5.

(10.) Hinton PS, Giordano C, Brownlie T, et al: Iron supplementation improves endurance after training in iron-depleted, nonanemic women. J Appl Physiol 2000; 84:1103-1111

(11.) Nielson P Nachtigall D: Iron supplementation in athletes. Current recommendation Sports Med 1998; 26: 207-11.

(12.) Chatard JC, Muijka I, Guy C, Lacour J: Anemia and iron deficiency in athletes Sports Med 1999; 27: 229-40.

Address correspondence to:

Edward R. Feller, M.D., 1 Randall Square, Suite 305, Providence, RI 02904; Telephone: 401-274-4800

COPYRIGHT 2003 American Running & Fitness Association

COPYRIGHT 2003 Gale Group

You May Also Like

“Losing weight in the New Year: fads and facts”

“Losing weight in the New Year: fads and facts” – Talking About Training Steven Jonas In the holiday season, the thoughts of many t…

2004 medical management of endurance events

2004 medical management of endurance events AMAA is pleased to announce that the American Road Race Medical Society is co-hosting the AMA…

Mel Williams, Ph.D. over 100 marathons and counting

Mel Williams, Ph.D. over 100 marathons and counting Jeff Venables Mel Williams, Ph.D., sighs and sheepishly offers that “Monday was…

Avoiding the perils of the peaks

High altitude illness: avoiding the perils of the peaks Francene Mason While in the picturesque southwestern Colorado mountain town…