title: Seasonal variation of 1,25-dihydroxyvitamin D and its association with  body mass index and age.
abstract: Under most normal conditions the serum level of 1,25-dihydroxyvitamin D is constant throughout the year, due to tight biochemical regulation. In contrast to this, the level of 25-hydroxyvitamin D is variable through the year, being largest in late summer, due to photosynthesis in the skin. The vitamin D status is usually assessed by measuring the level of the latter vitamin D derivative, rather than that of the presumably most active derivative 1,25(OH)2 vitamin D.We here show that for persons with a high body mass index (BMI) there is a significant seasonal variation, not only of 25(OH) vitamin D, but also of 1,25(OH)2 vitamin D. The variation seems to be largest for those with the poorest vitamin D status. Furthermore, there seems to be a correlation between the levels of the two vitamin D metabolites, indicating that the regulation of 1,25(OH)2 vitamin D is not always tight, notably in persons with high BMI.
authors.affiliation: Department of Radiation Biology, Rikshospitalet-Radiumhospitalet Medical Centre, Oslo, Norway.
authors.forename: Johan
authors.initials: J
authors.lastname: Moan
authors.forename: Zoya
authors.initials: Z
authors.lastname: Lagunova
authors.forename: Fedon Alexander
authors.initials: FA
authors.lastname: Lindberg
authors.forename: Alina Carmen
authors.initials: AC
authors.lastname: Porojnicu
mesh_terms: D000375:Aging / Q000502:physiology*; D015992:Body Mass Index; D004032:Diet; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012621:Seasons; D012737:Sex Factors; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; C104450:25-hydroxyvitamin D