Vitamin D therapy: the effects of race, skin colour and genotype

Jaya Sujatha; Gopal Kothandapani; Lucy Evans; Gossiel Fatma; Jennifer Walsh; Richard Eastell; Nick Bishop

doi:10.1530/boneabs.5.P97

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 (18–25 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.

Table 1 Results showing serum total and free 25OHD levels, calculated 25OHD and PTH levels at baseline and increment post supplementation, mean and SD.
		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.

Bone Abstracts

P97