Associations of diet, supplement use, and ultraviolet B radiation exposure with vitamin D status in Swedish women during winter

Abstract

Background: Vitamin D is produced endogenously after sun exposure but can also be obtained from natural food sources, food fortification, and dietary supplements. Objective: We aimed to determine the vitamin D status of women (61–86 y old) living in central Sweden (latitude 60°) during winter and its relation with vitamin D intake and exposure to ultraviolet B radiation. Design: In a cross-sectional study, we assessed the vitamin D status (serum 25-hydroxyvitamin D [25(OH)D]) of 116 women by using an enzyme immunoassay. The women completed questionnaires covering food habits, use of dietary supplements, and sun-related behavior. Results: In a multiple linear regression model, the main determinants of serum 25(OH)D concentrations (x̄ ± SD: 69 ± 23 mmol/L) were dietary vitamin D (6.0 ± 1.8 μg/d), travel to a sunny location during winter within the previous 6 mo (26%), and the use of dietary supplements (16%). There was no association between serum 25(OH)D status during the winter and age, time spent outdoors, the use of sunscreen, or skin type. Serum 25(OH)D concentrations increased by 25.5 nmol/L with 2–3 servings (130 g/wk) fatty fish/wk, by 6.2 nmol/L with the daily intake of 300 g vitamin D–fortified reduced-fat dairy products, by 11.0 nmol/L with regular use of vitamin D supplements, and by 14.5 nmol/L with a sun vacation during winter. Among nonsupplement users without a wintertime sun vacation, 2–3 servings fatty fish/wk increased serum vitamin D concentrations by 45%. Conclusion: Fatty fish, vitamin D–fortified reduced-fat dairy products, regular supplement use, and taking a sun vacation are important predictors for serum concentrations of 25(OH)D during winter at a latitude of 60°.