DECREASED NITRIC-OXIDE LEVELS AND BONE TURNOVER IN AMENORRHEIC ATHLETES WITH SPINAL OSTEOPENIA

Amenorrheic athletes have been likened to postmenopausal women, with l ow estrogen levels and osteopenia. It has been suggested that estrogen exerts its antiresorptive actions on bone via a nitric oxide (NO)-dep endent mechanism. This study investigated whether the mechanism of bon e loss in amenorrheic athletes is similar to that of postmenopausal wo men with reduced NO levels and high bone turnover. Eleven amenorrheic athletes, 15 eumenorrheic athletes, and 10 sedentary controls were stu died. Spine and hip bone mineral density was measured using dual-energ y x-ray absorptiometry. Bone turnover was assessed by biochemical mark ers of formation (osteocalcin and bone-specific alkaline phosphatase) and resorption (deoxypyridinoline). NO metabolites were measured from 24-h urine samples using a chemiluminescence assay. Spine, but not hip , bone mineral density was reduced in the amenorrheic group, compared with the eumenorrheic (P = 0.0001) and control (P = 0.04) groups. Oste ocalcin, bone-specific alkaline phosphatase, and deoxypyridinoline wer e similar in all groups. NO metabolites were lower in the amenorrheic group, compared with controls (P = 0.035), despite a higher dietary in take of nitrates. Unlike postmenopausal women, amenorrheic athletes do not have raised bone turnover but do have reduced NO metabolites and spinal osteopenia. The results show, however, that reduced NO producti on is a common denominator in both conditions and further support the importance of NO in estrogen-mediated protection of skeletal mass and strength.