Serum 25(OH)D levels after oral vitamin D 3 supplementation and UVB exposure correlate

The inter-individual variation in 25(OH)D increase (Δ25(OH)D ) after vitamin D supplementation was determined and compared with the UVB irradiation response. Nineteen Danish participants received 85 μg vitamin D (cholecalciferol) daily for nine weeks with regular serum 25(OH)D measurements. These participants had three years earlier taken part in a 9-week controlled UVB study. The Δ25(OH)D was not confounded by ambient UVB, BMI or ethnicity. Δ25(OH)D was 53 nmol L and almost identical to Δ25(OH)D (52 nmol L ) after UVB. Δ25(OH)D ranged from 17 to 91 nmol L (span 74 nmol L ) and was about half of that observed after UVB irradiation (span 136 nmol L ). The interquartile ranges for vitamin D supplementation (38.8-71.4 nmol L , span: 32.6 nmol L ) and UVB irradiation (35.7-65.4 nmol L , span: 29.7 nmol L ) were similar indicating a comparable response of the two interventions. As the 25(OH)D start levels (R = 0.398, P = 3.8 × 10 ), 25(OH)D end levels (R = 0.457, P = 1.5 × 10 ) and Δ25(OH)D (R = 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 -induced and UVB-induced Δ25(OH)D . A combined model including the influence of these four SNPs and the 25(OH)D start level explained 86.8% (P = 1.6 × 10 ) of the individual variation after vitamin D supplementation. The inter-individual variation in the two interventions was comparable and had no common demographic but a partly common genetic background.