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Objectives: The aim of the study was to evaluate vitamin D status and effects of vitamin D intervention on bone mineral density (BMD) and content (BMC) in children with fair and dark skin in Sweden during winter.

Methods: In a 2-center prospective double-blinded randomized intervention study 5- to 7-year-old children (n = 206) with fair and dark skin in Sweden (55 degrees N-63 degrees N) received daily vitamin D supplements of 25 mu g, 10 mu g, or placebo (2 mu g) during 3 winter months. We measured BMD and BMC for total body (TB), total body less head (TBLH), femoral neck (FN), and spine at baseline and 4 months later. Intake of vitamin D and calcium, serum 25-hydroxy vitamin D (S-25 [OH]D), and related parameters were analyzed.

Results: Despite lower S-25(OH)D in dark than fair-skinned children, BMD of TB (P = 0.012) and TBLH (P = 0.002) and BMC of TBLH (P = 0.04) were higher at baseline and follow-up in those with dark skin. Delta (Delta) BMD and BMC of TB and TBLH did not differ between intervention and placebo groups, but FN-BMC increased more among dark-skinned children in the 25 mu g (P = 0.038) and 10 mu g (P = 0.027) groups compared to placebo. We found no associations between Delta S-25(OH)D, P-parathyroid hormone, P-alkaline phosphatase, and Delta BMD and BMC, respectively.

Conclusions: BMD and BMC remained higher in dark- than fair-skinned children despite lower vitamin D status. Even though no difference in general was found in BMD or BMC after vitamin D intervention, the increase in FN-BMC in dark-skinned children may suggest an influence on bone in those with initially insufficient vitamin D status.