The association between physical activity and forearm bone mineral density in healthy premenopausal women

Purpose: To analyze the association between recreational and occupational physical activity and forearm bone mineral density (BMD) in healthy premenopausal women. Methods: During 1984-1986, a population-based health survey (HUNT 1) was conducted among women and men aged >19 years in Nord-Trondelag county in Norway. The second, follow-up survey (HUNT 2) was conducted during 1995-1997. The subjects in this study consist of healthy premenopausal women (n = 1396) <45 years old in the year of participation of HUNT 2 who had undergone distal and ultradistal radius densitometry in 1995-1997, performed with single-energy x-ray absorptiometry. Results: Women with the highest scores of estimated combined recreational and occupational physical activity (PA) in 1984 and 1995 had significantly higher BMD in the distal radius (mean BMD 0.487 compared with mean BMD 0.480 among those with a low combined PA score) (p for trend = 0.04). At the ultradistal site of the radius, women with a high combined PA score had mean a BMD = 0.403 compared with women with low PA scores (mean BMD = 0.384) (p for trend = 0.017). After adjusting for age, marital status, smoking, amenorrhea, body mass index (BMI), and daily milk consumption, the associations remained the same or got even stronger. Conclusions: The small group of women in the highest category of PA had a significantly higher forearm BMD and the smallest risk of low BMD. Important unanswered questions remain about the optimal relationship between intensity, amount and type of PA, and BMD and later risk of osteoporosis. Further research on BMD as a surrogate measure of structural and architectural bone quality and the sensitivity of different measuring sites for estimation of the effect of PA on bone is warranted.