Free vitamin D level much higher in Asians vs Caucasians after 150,000 IU dose – Aug 2018

Effect of vitamin D supplementation on free and total vitamin D: a comparison of Asians vs Caucasians.

Clin Endocrinol (Oxf). 2018 Aug 1. doi: 10.1111/cen.13825. [Epub ahead of print]
Gopal-Kothandapani JS1, Evans LF2, Walsh JS2, Gossiel F2, Rigby AS3, Eastell R2, Bishop NJ1.
1 Department of Oncology and Metabolism, University of Sheffield, Sheffield, UK.
2 Academic Unit of Bone Metabolism, University of Sheffield, Sheffield, UK.
3 Hull York Medical School, Faculty of Health, University of Hull Hull,, UK.

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 (150,000 IU) administered to young Asian and Caucasian men.

DESIGN:
Prospective, single centre clinical trial PARTICIPANTS: Sixty young men (18-25yr) 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 (25OHD); calculated and directly measured free 25OHD; 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 25OHD (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 25OHD (16.7 [10.4] vs 17.8 [7.5] pmol/l p=0.6530). After dosing, total 25OHD rose similarly in each group (≈56 nmol/l), but measured free 25OHD 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 25OHD in Caucasians, but not in Asians.

CONCLUSIONS:
Asian compared with Caucasian males had a larger increment in measured free 25OHD following 150,000 units vitamin D3, possibly reflecting differences in DBP affinity for 25OHD. Ethnicity should be considered when devising guidelines for the treatment of vitamin D deficiency.