Effect of vitamin D supplementation on free and total vitamin D: A comparison of Asians and Caucasians

Summary Objectives It is well established that UK Asians typically have lower vitamin D levels than Caucasians. It is also known that vitamin D binding protein ( DBP ) is lower in some races than Caucasians. To investigate how ethnicity, skin colour and genetic variation affect the response to vitamin D (15000 IU) administered to young Asian and Caucasian men. Design Prospective, single‐centre clinical trial. Participants Sixty young men (18‐25 year) of Asian (n = 30) and Caucasian (n = 30) origin. Measurements We measured serum calcium, phosphate, magnesium, alkaline phosphatase, albumin, parathyroid hormone; total 25 hydroxyvitamin D (25 OHD ); calculated and directly measured free 25 OHD ; DBP at baseline and 4 weeks; DBP genotype, skin colour (Fitzpatrick scale), dietary vitamin D and calcium intake at baseline; and urine calcium:creatinine ratio at baseline, 1 and 4 weeks. Results At baseline, Asians had lower serum total 25 OHD (26.4 [13.7] vs 34.1 [12.3] nmol/L P  = 0.0272) and DBP (6.7 [3.4] vs 9.6 [4.4] nmol/L; P  = 0.0065) but similar free 25 OHD (16.7 [10.4] vs 17.8 [7.5] pmol/L P  = 0.6530). After dosing, total 25 OHD rose similarly in each group (≈56 nmol/L), but measured free 25 OHD rose more in Asians (18.1 [9.4] vs 12.2 [13.3] pmol/L P  = 0.0464). Lower DBP at baseline, possibly reflecting genotype differences, was associated with a greater change in measured free 25 OHD in Caucasians, but not in Asians. Conclusions Asian compared with Caucasian males had a larger increment in measured free 25 OHD following 150 000 units vitamin D3, possibly reflecting differences in DBP affinity for 25 OHD . Ethnicity should be considered when devising guidelines for the treatment of vitamin D deficiency.