Background: It is well established that Asians have lower levels of vitamin D (25OHD) when compared to Caucasians. Vitamin D binding protein (DBP) levels are also lower in some races than in Caucasians.
Objectives: i) To find out whether DBP is lower in Asians; ii) To find out whether free 25OHD is lower in Asians; iii) To find out whether PTH is increased in Asians and interpret this in relation to 25OHD levels and iv) To find out whether the increment in 25OHD levels is the same in Asians.
Methods: Prospective single centre clinical trial involving sixty healthy men (1825 years): Caucasians (n=30) and Asians (n=30). Fasting serum samples were collected immediately before and 4 weeks after vitamin D3 (150,000 IU) administration. We measured total 25OHD, free 25OHD (Future Diagnostics), albumin, DBP (Genways), DBP genotype, and we calculated free 25OHD.
Results: All subjects achieved a >25 nmol/l increment in total 25OHD level following vitamin D administration (Table 1). At baseline, Asians had significantly lower serum total 25OHD and DBP levels, similar serum and calculated free 25OHD and higher PTH levels compared to Caucasians. Four weeks after supplementation, increment in serum total 25OHD was not different between the two groups however the increment in free 25OHD appears to be higher in Asians.
|Serum Total 25OHD (nmol/l)||Serum DBP (umol/l)||Measured Free 25OHD (pmol/l)||Calculated Free 25OHD (pmol/l)||PTH (ng/l)|
|Baseline||Caucasians||34.1 (12.3)||6.6 (3.0)||17.8 (7.5)||13.6 (7.8)||44.6 (14.2)|
|Asians||26.3 (13.7)||4.7 (2.3)||16.7 (10.4)||11.9 (6.8)||69.8 (38.6)|
|*P-value <0.05||P value||*0.04||*0.01||0.65||0.38||*0.002|
|Increment||Caucasians||56.7 (18.3)||0.31 (2.0)||12.2 (13.3)||24.4 (14.5)||2.2 (14.2)|
|Asians||56.2 (12.6)||0.24 (2.0)||18.1 (9.4)||29.4 (20.1)||−4.7 (27.7)|
|*P-value <0.05||P value||0.90||0.90||*0.05||0.29||0.24|
Conclusions: Asians may well be 25OHD deficient, and the higher PTH in Asians appears to be due to low total 25OHD, rather than the free 25OHD. DBP is lower in Asians, and this is the likely reason why free 25OHD is not lower in Asians. Despite a similar response in increment of total 25OHD between the two groups, a larger increment in free 25OHD in Asians prompts us to re-consider the existing one size fits all approach for vitamin D treatment.
14 May 2016 - 17 May 2016