Sport and home physical activity are independently associated with bone density

To study the relations between four domains of physical activity-sport, home, work, and active living-and bone mineral density (BMD).

Baseline data from African-American (N = 544), Caucasian (N= 1044), Chinese (N= 230), and Japanese (N= 239) participants, aged 42-52 yr, from the study of Women's Health Across the Nation were analyzed. BMD was measured with Hologic 2000 or 4500A densitometers. Physical activity was assessed with the Kaiser Physical Activity Scale, which rates each domain of activity between 1 (low) and 5 (high). Multiply adjusted linear regression models were used to estimate the relations between each activity domain and BMD.

The mean and median values of sport, home, work, and active living each approximated the midpoint of the scale and did not differ substantially among ethnic groups. Scores for each domain of activity were not highly correlated, with r values ranging between -0.03 and 0.33. Independent of age, body mass index, ethnic group, alcohol use, dietary calcium, smoking, menopause status, SWAN site, and other domains of physical activity, higher sport activity was statistically significantly associated with greater BMD at the lumbar spine (P= 0.008), femoral neck (P= 0.0002), and total hip (P< 0.0001). More home physical activity was associated with higher BMD at the spine (P= 0.049) and femoral neck (P= 0.008). Neither work physical activity nor active living was related to BMD at any bone site.

These results highlight the need to consider domain-specific physical activity in relation to health outcomes in women.