Energy Deficiency Suppresses Bone Turnover in Exercising Women with Menstrual Disturbances

Context In exercising women, energy deficiency can disrupt the balance of bone formation and resorption, resulting in bone loss and an altered rate of bone turnover, which may influence future bone mineral density and fracture risk. Objective To assess the effects of energy status and estrogen status on bone turnover. Design Cross-sectional. Setting The Women's Health and Exercise Laboratory at Pennsylvania State University. Participants Exercising women (n = 109) operationally defined as energy deficient or replete based on total triiodothyronine concentration and as estrogen deficient or replete based on menstrual cycle history and reproductive hormone metabolites. Main Outcome Measures Bone formation index [procollagen type I N-terminal propeptide (P1NP) concentration corrected for average P1NP concentration in healthy reference group, i.e., [P1NP] i /median [P1NP] ref ], bone resorption index [serum C-terminal telopeptide (sCTx) concentration corrected for average sCTx concentration in healthy reference group, i.e., [sCTx] i /median [sCTx] ref ], bone balance (ratio of bone formation index to bone resorption index to indicate which process predominates), and bone turnover rate (collective magnitude of bone formation index and bone resorption index to indicate overall amount of bone turnover). Results The combination of energy and estrogen deficiency resulted in less bone formation and a lower rate of bone turnover compared with women who were estrogen deficient but energy replete. Regardless of estrogen status, energy deficiency was associated with decreased bone resorption as well. No main effects of estrogen status were observed. Conclusions The results highlight the critical role that adequate energy plays in the regulation of bone turnover, especially bone formation, in exercising women with menstrual disturbances.