Vitamin D status in North Greenland is influenced by diet and season: indicators of dermal 25-hydroxy vitamin D production north of the Arctic Circle

Vitamin D status, as measured by serum 25-hydroxy vitamin D (s-25OHD), is important to human health. Dermal 25OHD production depends on UVB light that is influenced by latitude. We aimed to identify factors important to the production of s-25OHD in Arctic people and investigated subjects living in the town of Ilulissat and the settlement of Saqqaq in North Greenland (70°N) during the four seasons. Participants were enrolled with a balanced representation of non-Inuit and Inuit in Ilulissat and Inuit in Saqqaq, men and women, aged 30-39 and 40-49 years. Supplement use, hours spent outdoors and other lifestyle factors were determined by questionnaires. Scores of traditional Inuit food intake were computed from a FFQ at inclusion, and frequencies of intake were recorded at each visit. s-25OHD concentration was measured. There were sixty-four Inuit and thirty-three non-Inuit participants. Inuit food score < 40 % was found in 87, 64 and 48 % of non-Inuit, Inuit in Ilulissat and Inuit in Saqqaq participants, respectively (P= 0·009). Inuit diet associated positively with s-25OHD (P< 0·001). s-25OHD concentration was lower in non-Inuit than in Inuit participants (spring/summer/autumn/winter/average: 30·3 v. 36·8/43·2 v. 44·7/43·6 v. 48·6/32·8 v. 43·5/39·0 v. 44·6 nmol/l, P= 0·002/0·62/0·19/ < 0·001/0·011, respectively). s-25OHD levels differed with season (Inuit, P< 0·001; non-Inuit, P< 0·001) as did diet (Inuit, P< 0·001; non-Inuit, P< 0·001) and hours spent outdoors (Inuit, P< 0·001; non-Inuit, P= 0·012). s-25OHD level was influenced by diet (P< 0·001), season (P< 0·001), origin (P= 0·001), residence (P= 0·013) and sex (P= 0·026). We conclude that the season influenced vitamin D status in Arctic populations beyond diet, ethnicity and vitamin intake. This suggests dermal 25OHD production at a high latitude of 70°N.