Bone Density in Premenopausal Women: Effects of Age, Dietary Intake, Physical Activity, Smoking, and Birth-control Pills

The effects of age, calcium, smoking, and physical activity on appendicular and axial bone mineral density (BMD) were evaluated in a 2-y study of 200-300 healthy young women aged 20-39 y. There was no cross-sectional change of BMD with age or longitudinal change with bone loss. No effect of birth-control pills on BMD was seen. There also was no association of calcium intake with BMD and/or with BMD changes. Current calcium intake was not a significant influence on BMD in this age group. Daily activity had no effect on BMD and there was no apparent additive interaction of activity and calcium intake on BMD. Smokers had significantly lower spine BMD and a tendency for lower BMD at other sites. Body weight was a better predictor of BMD than was any other factor. There was no association of BMD or BMD changes with both urinary calcium and hydroxyproline normalized for creatinine.