Amenorrhea in Olympic marathon runners

Women who exercise heavily may develop secondary amenorrhea. Since the mechanism of so-called "runner's amenorrhea" has not been conclusively established, the authors examined the occurrence of amenorrhea in one of the most intensively exercising groups of female runners in the United States (average, 70 miles/week): those women participating in the marathon trials for the 1984 Olympics. Nineteen percent of these Olympic runners were amenorrheic. When compared with eumenorrheic marathon runners, these amenorrheic runners were significantly (P less than 0.05) younger (24.8 +/- 1.2 [standard error of the mean] versus 30.8 +/- 0.8 years), lighter (108.4 +/- 2.5 versus 114.6 +/- 1.7 lb), and leaner (11.2 +/- 0.5 versus 12.5 +/- 0.3% body fat). There were no differences between the two groups in weekly training mileage, proportion completing the marathon trial, finishing time, basal serum prolactin, or postmarathon serum prolactin. Although basal serum cortisol was slightly higher in the amenorrheic group (26.6 +/- 0.8 versus 22.3 +/- 0.7 micrograms/dl; P less than 0.05), postmarathon serum cortisol was similar in the two groups. This study supports the concept that training intensity above a certain threshold seems to have little effect on the development of runner's amenorrhea, and vigorously training national caliber marathon runners have a lower incidence of amenorrhea than previously predicted.