Running induces menstrual disturbances but bone mass is unaffected, except in amenorrheic women

To investigate the prevalence of exercise-related menstrual and sex hormonal disturbances and the effect of exercise on bone mass and metabolism in female runners at various training levels.

Two hundred five premenopausal women (running 0 to 140 km a week) were recruited from a large population of female runners who had responded to a questionnaire regarding exercise habits. Maximum oxygen uptake was determined by treadmill testing. Gynecologic status was assessed on entries in a menstrual calendar and by transvaginal ultrasonography; sex hormonal status was measured three times with 10-day intervals. Bone mass was measured in the lumbar spine, proximal femurs, and total body by dual-energy x-ray absorptiometry, and in the forearm by single-photon absorptiometry. Bone turnover was assessed by measurement of plasma osteocalcin, serum alkaline phosphatase, and urinary calcium and hydroxyproline.

Sex hormonal disturbances were significantly related to training intensity. Compared with the normally active women, the baseline levels and fluctuations of estradiol and progesterone in the elite runners were reduced by up to 25% to 44% (0.01 < p < 0.05). The prevalence of amenorrhea increased from 1% in the normally active subjects to 11% in the elite runners. No statistically significant relation was found between running activity and bone mineral measurements or bone turnover. However, the group of amenorrheic runners had a 10% reduction in lumbar bone density as compared with the normally menstruating runners (p < 0.05), but the bone turnover was similar.

In the large majority of the female runners, no skeletal affection was found despite significant sex hormonal and menstrual disturbances. Only the runners with amenorrhea might be at increased risk of osteoporosis.