Associations of Calcium Intake and Physical Activity With Bone Density and Size in Premenopausal and Postmenopausal Women: A Peripheral Quantitative Computed Tomography Study

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Abstract
The purpose of this cross‐sectional study was to examine the impact of long‐term physical activity (PA) and calcium intake on non‐weight‐bearing radius and weight‐bearing tibia. Altogether, 218 healthy, nonsmoking women, [92 premenopausal women, mean age, 32.6 years (SD, 2.2 years), and 126 postmenopausal women, mean age, 67.3 years (SD, 2.0 years)] participated. The subjects were divided according to their habitual levels of physical activity (PA+ or PA−) and calcium intake (Ca+ or Ca−). The distal end and shaft regions of the radius and tibia were evaluated with peripheral quantitative tomography (pQCT). For the shaft regions, bone mineral content (BMC), cortical cross‐sectional area (CoA), cortical density (CoD), and bone strength index, that is, 1‐11.9% of the density‐weighted section modulus (BSI) were determined. For the distal ends, BMC, total cross‐sectional area (ToA), trabecular density (TrD), and BSI were determined. The BMC at the distal radius in the young PA+ group was 6.6% (95% CI, 1‐to 11.9%) lower than that of the PA− group. A similar nonsignificant trend was found for the radial shaft. The radial shaft showed a mechanically more competent structure among the older subjects with a BSI 8.5% (95% CI, 1.8‐15.6%) higher in the older PA+ group than in the older PA− group. The associations between calcium intake and the radial bone characteristics were systematically positive in both age groups. PA seemed to benefit the distal tibia. In the younger age group the TrD was 6.9% (95% CI, 1.8‐12.4%) higher in the PA+ group, and in the elderly the BMC was 5% (95% CI, 0.3‐9.9%) higher in the PA+ group than in the PA− group. Note that in the younger age group the ToA was 5.1% (95% CI, 0‐9.1%) smaller in the PA+ group than in the PA− group, and in the older age group the ToA was 4.2% (95% CI, −0.3‐8.9%) greater in the PA+ group than in the PA− group. The association of PA and bone characteristics at the tibial shaft was positive in both age groups (statistically significant for the older subjects). The tibial shaft BSI of the older PA+ group was 8.6% (95% CI, 2.6‐14.9%) better than that of the old PA− group. There was no association between calcium intake and the tibial bone characteristics in either age group. In conclusion, high calcium intake was positively associated with a mechanically competent structure in the radius among both younger and older women, whereas the influence of PA did not become apparent until older ages. PA seemed to benefit particularly the weight‐bearing tibia, whereas calcium intake was not associated with the tibia.