Vitamin D status and its determinants in children and adults among families in late summer in Denmark

The impact of the familial relationship on vitamin D status has not been investigated previously. The objective of the present cross-sectional study was to assess serum 25-hydroxyvitamin D (25(OH)D) concentration and its determinants in children and adults among families in late summer in Denmark (56 degrees N). Data obtained from 755 apparently healthy children (4-17 years) and adults (18-60 years) recruited as families (n 200) in the VitmaD study were analysed. Blood samples were collected in September-October, and serum 25(OH)D concentration was measured by liquid chromatography-tandem MS. Information on potential determinants was obtained using questionnaires. The geometric mean serum 25(OH)D concentration was 72.1 (interquartile range 61.5-86.7) nmol/l (range 9-162 nmol/l), with 9% of the subjects having 25(OH)D concentrations <50 nmol/l. The intra-family correlation was 0.27 in all subjects, 0.24 in the adults and 0.42 in the children. Serum 25(OH)D concentration was negatively associated with BMI (P<0.001) and positively associated with dietary vitamin D intake (P=0.008), multivitamin use (P=0. 019), solarium use (P=0.006), outdoor stay (P=0.001), sun preference (P=0. 002) and sun vacation (P<0.001), but was not associated with lifestyle-related factors in the adults when these were assessed together with the other determinants. In conclusion, the majority of children and adults among the families had serum 25(OH)D concentrations >50 nmol/l in late summer in Denmark. Both dietary and sun-related factors were determinants of vitamin D status and the familial component was stronger for the children than for the adults.