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.