Seasonality of UV-radiation and vitamin D status at 69 degrees north.
Brustad M, Edvardsen K, Wilsgaard T, Engelsen O, Aksnes L, Lund E.
Photochem Photobiol Sci. 2007 Aug;6(8):903-8. Epub 2007 Jun 27.
PMID: 17668121
The generally high dietary intakes of vitamin D, especially in winter, mask largely the effect of seasonal variation in UV-exposure, causing an atypical seasonal variation in vitamin D status. The UV-hour variable significantly predicted 25(OH)D levels in blood when adjusted for intakes and artificial UV-radiation exposure and sun holidays abroad.