Does hyperinsulinemia preserve bone?

OBJECTIVE - Obesity and NIDDM are each associated with increased bone mineral density (BMD). We therefore hypothesize that hyperinsulinemia is an osteogenic factor. RESEARCH DESIGN AND METHODS - Subjects consisted of 411 men and 559 women aged 50-89 years who were participants in the Rancho Bernardo Heart and Chronic Disease Study and were not diabetic by history or oral glucose tolerance test. Fasting and 2-h postchallenge insulin were measured by radioimmunoassay. Bone mineral density mas measured at the midshaft radius with single photon absorptiometry and at the lumbar spine and hip with dual energy X-ray absorptiometry. RESULTS - Multiple regression analyses indicated that among men, a significant insulin-BMD association at the hip was no longer apparent after adjusting for covariates. Among women, fasting insulin was significantly and positively associated with bone density of the radius and spine (P < 0.05), independent of age, BMI, waist-hip ratio, postmenopausal estrogen use, age at menopause, thiazide use, family history of diabetes, current cigarette smoking, and exercise. Each 10 mu U/ml increase in fasting insulin was associated with an increase of 0.33 and 0.57 g/cm(2) of the radius and spine, respectively. CONCLUSIONS - Hyperinsulinemia may be responsible for part of the observed association of both diabetes and obesity with BMD in women.