Endocrine Abstracts

Background: Over-dosing and under-dosing of vitamin D in children and young people appears to be common, based on our audit of current practice. The contribution of ethnicity, skin colour, and vitamin D binding protein (VDBP) genotype has not been fully explored during vitamin D treatment.

Objective: To investigate how ethnicity/skin colour and genetic variation affect the response to 150 000 units of vitamin D administered to young adults of white Caucasian and South or East Asian origin.

Method: Prospective single centre clinical trial. Sixty healthy males aged 18 –25 years, white Caucasian (n=30) and South or East Asian (n=30) were recruited. Fasting i) blood samples for total 25-hydroxyvitamin D (25OHD), VDBP (Genways polyclonal assay), VDBP genotype, bone biochemistry, albumin, PINP and CTX, calculated free and bioavailable 25OHD and ii) urine for calcium:creatinine ratio were examined before and after an administration of single dose of 150 000 IU of vitamin D3. Anthropometry, skin colour grading, and vitamin D and calcium intake assessment were undertaken.

Results: All subjects achieved a ≥25 nmol/l increment in 25OHD level following vitamin D administration. Asians had significantly lower serum 25OHD and VDBP levels at baseline but similar estimated free and bioavailable 25OHD to whites. VDBP levels remained significantly lower in.

Asians post administration with no difference in total or free/bioavailable 25OHD compared to whites. No hypercalcaemia/hypercalciuria observed in any subject. Skin colour, race and VDBP genotype did not influence variation in treatment response.

Conclusion: 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.