Table 1: Bone biochemistry and Turnover markers Serum Total 25OHD (nmol/L) Serum VDBP (umol/L) Calculated Free 25OHD (nmol/L) Calculated Bioavailable 25OHD (nmol/L) PTH (ng/L) PINP (ng/ml) CTX (ng/ml) Baseline Whites 34.06(12.30) 6.59(3.03) 0.014(0.008) 0.015(0.007) 44.60 (14.24) 107.2 (40.90) .82 (.26) Asians 26.34(13.72) 4.73(2.27) 0.012(0.007) 0.020(0.010) 69.83 (38.62) 82.0 (36.72) .68 (.21) p value *0.04 *0.01 0.37 0.26 *0.002 *0.002 *0.02 Post dosing Whites 90.79(16.71) 6.495(2.83)

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... .018) 0.015(0.007) 49.37 (20.28) 113.83 (46.5) .78 (.24) Asians 82.79(14.04) 4.64(2.15) 0.04(0.02) 0.020(0.011) 65.16 (32.77) 92.3 (40.2) .64 (.22) p value 0.17 *0.008 0.47 0.16 *0.007 *0.025 *0.02 Asians had significantly lower serum 25OHD and VDBP levels at baseline but similar free and bioavailable 25OHD as whites. VDBP levels remained significantly lower in Asians post dosing with no difference in total or free /bioavailable 25OHD (table 1) . All subjects achieved a ≥ 25nmol/L increment in 25OHD. No hypercalcaemia / hypercalciuria observed in any subject. Results Skin colour, race & VDBP genotype did not influence variation in treatment response as demonstrated by the graphs below. * p-value <0.05 Conclusions Our results show that a single dose of vitamin D is sufficient and safe to increase the 25OHD level to >50 nmol/l irrespective of, and unaffected by, skin colour, ethnicity, and genotype. Background Multiple factors influence vitamin D status in children and young people. It is unclear to what extent such factors influence the response to vitamin D treatment. Aim To investigate how skin colour, race and genetic variation affect the response to vitamin D (150,000 units) administered to young adults of White Caucasian & South /East Asian origin.