Serum 25(OH)D levels after oral vitamin D3 supplementation and UVB exposure correlate

Background The inter-individual variation in 25(OH)D-3 increase (Delta 25(OH)D-3) after vitamin D-3 supplementation was determined and compared with the UVB irradiation response. Methods Nineteen Danish participants received 85 mu g vitamin D-3 (cholecalciferol) daily for nine weeks with regular serum 25(OH)D-3 measurements. These participants had three years earlier taken part in a 9-week controlled UVB study. The Delta 25(OH)D-3 was not confounded by ambient UVB, BMI or ethnicity. Results Delta 25(OH)D-3 was 53 nmol L-1 and almost identical to Delta 25(OH)D-3 (52 nmol L-1) after UVB. Delta 25(OH)D-3 ranged from 17 to 91 nmol L-1 (span 74 nmol L-1) and was about half of that observed after UVB irradiation (span 136 nmol L-1). The interquartile ranges for vitamin D-3 supplementation (38.8-71.4 nmol L-1, span: 32.6 nmol L-1) and UVB irradiation (35.7-65.4 nmol L-1, span: 29.7 nmol L-1) were similar indicating a comparable response of the two interventions. As the 25(OH)D-3 start levels (R-2 = 0.398, P = 3.8 x 10(-3)), 25(OH)D-3 end levels (R-2 = 0.457, P = 1.5 x 10(-3)) and Delta 25(OH)D-3 (R-2 = 0.253, P = 0.028) between both interventions were correlated, this suggested a possible common individual background for the variation. Four pigment SNPs influenced the variation in the vitamin D-3-induced and UVB-induced Delta 25(OH)D-3. A combined model including the influence of these four SNPs and the 25(OH)D-3 start level explained 86.8% (P = 1.6 x 10(-35)) of the individual variation after vitamin D-3 supplementation. Conclusion The inter-individual variation in the two interventions was comparable and had no common demographic but a partly common genetic background.