It is unknown whether there is an association between vitamin D status and bone geometry parameters in older South Asian women, and whether this differs from same-age Caucasian women. This is the first study, to the authors' knowledge, to assess the relationship between vitamin D status and peripheral quantitative computed tomography (pQCT) indices of bone architecture in older South Asian women. To measure radius bone structure, pQCT scans (Stratec X2000L) at the distal (4%) and mid-shaft (66%) sites were undertaken in n = 18 South Asian (mean age 63.5 y+/−3.6) and n = 50 Caucasian women (mean age 65.9 y+/−4.8). A fasting blood sample was obtained for assessment of vitamin D status (25-hydroxyvitamin D). Partial correlations assessed the relationship between vitamin D status and the radial bone indices. Unadjusted and BMI adjusted data can be seen in the table.
≠SSIpol = polar strength strain index (predicted measure of ability to resist torsion forces); ≠≠Fracture Load = predicted amount of Newtons required to fracture the bone. Unadjusted = unadjusted data; BMI = BMI (Body Mass Index) adjusted data.
For BMI adjusted data, in Caucasians, there were significant correlations between vitamin D status and bone mass (r = 0.379 p = 0.013), strength strain index (r = 0.337 p = 0.029), area of the cortical layer (r = 0.343 p = 0.026) and predicted fracture load (r = 0.337 p = 0.029) at the mid-shaft (66%) site. There were also positive correlations between vitamin D status and total area (r = 0.327 p = 0.035) at the distal (4%) site. Therefore, in Caucasians, increased vitamin D was associated with increased bone mass, size and measures of bone strength at both distal and mid shaft sites. For Asians, the only significant correlations between vitamin D status and the bone parameters were for trabecular density (r = 0.547 p = 0.035) at the distal (4%) site, and there were no significant correlations at the mid shaft (66%) site. This suggests, in Asians, increased vitamin D status was only associated with increased density in the trabecular layer, and only at the distal site (4%). Overall, vitamin D appears to be positively correlated with size, strength and mass parameters in Caucasians, and positively correlated with trabecular density in South Asians. Therefore, in both ethnic groups, vitamin D is associated with positive effects on radial bone parameters, and a stronger bone structure. However, the underlying mechanisms in the two ethnic groups may be different. Further research is required to investigate these differences.