Factors affecting bone loss in female endurance athletes: a two-year follow-up study.

Background: Low bone mass leading to stress fractures is a well-known and yet unsolved problem among female athletes.

Purpose: To quantify the rate of bone loss in healthy female athletes and investigate the effects of estrogen and vitamin K supplementation on bone loss.

Study Design: Prospective cohort study.

Methods: We classified 115 female endurance athletes into amenorrheic, eumenorrheic, or estrogen-supplemented groups and randomized them to receive either placebo or vitamin K(1). The bone mineral densities of the subjects' femoral neck and lumbar spine were measured at baseline and after 2 years.

Results: Bone mineral density in the lumbar spine remained constant, but bone density in the femoral neck had decreased significantly after 2 years in all three subgroups. The decrease was higher in amenorrheic (-6.5% +/- 4.0%) than in eumenorrheic (-3.2% +/- 4.1%) and estrogen-supplemented athletes (-3.9% +/- 3.1%). Supplementation with vitamin K did not affect the rate of bone loss.

Conclusions: The rate of bone loss in all three subgroups of female athletes was unexpectedly high; neither estrogen nor vitamin K supplementation prevented bone loss.

Clinical Relevance: High-intensity training maintained over several years must be regarded in women as a risk factor for osteoporosis, and protocols for optimal treatment should be developed.