RELATIONS OF ENDOGENOUS ANABOLIC HORMONES AND PHYSICAL-ACTIVITY TO BONE-MINERAL DENSITY AND LEAN BODY-MASS IN ELDERLY MEN

OBJECTIVE It has been proposed that declining activities of the somato trophic or gonadotrophic axes, or sedentary life style, are partial ca uses for geriatric losses of bone mineral density (BMD) and of lean bo dy mass (LBM). The present study tested these hypotheses by determinin g, in both free-living and institutionalized elderly men, the correlat ions of bone mineral density (BMD), total body bone mineral content (T BBMC) and lean body mass (LBM) with the following predictor variables: age, body mass index, body weight, serum insulin-like growth factor I (IGF-I), serum testosterone, habitual physical activity and mobility. SUBJECTS Forty-nine independent, community-dwelling older men, and 49 men of similar age residing in two Veterans Administration extended c are facilities. The age range was 58-95 years. MEASUREMENTS Serum IGF- I and testosterone were measured by radioimmunoassay. Habitual physica l activity in the independent men and mobility in the institutionalize d men were estimated by standard instruments. LBM and bone status at n ine skeletal sites were determined by dual X-ray absorptiometry. RESUL TS The BMD and TBBMC values of the free living men were 4-20% higher t han those of the institutionalized men. In the independent old men, se rum testosterone was the strongest predictor of BMD and TBBMC, while a ge was the only predictor of LBM. In the chronically institutionalized men, age, body weight and immobility were the strongest predictors of body composition, and testosterone was correlated only with femoral n eck BMD. CONCLUSIONS In aging independent men, low levels of testoster one are associated with demineralization of the skeleton. Immobility a nd under-weight are associated with the osteopenia of old men residing in nursing homes. In this cross-sectional study of elderly men, there was no evidence of a relation of the somatotrophic axis to bone statu s or LBM, or of the gonadotrophic axis to LBM.