Objective: To assess vitamin D status and the impact of three fish meals consisting of cod liver and fresh cod-liver oil on the plasma level of vitamin D metabolites in an area with high consumption of cod liver and cod-liver oil.
Design: Experimental field study.
Methods: Thirty-two volunteers from the Skjervøy (70 degrees N) municipality in northern Norway were recruited to consume three traditional mølje meals, consisting of cod, cod liver, fresh cod-liver oil and hard roe, in one week. The liver and fresh cod-liver oil consumed by the participants were weighed and recorded. Blood samples were collected before the first meal, and subsequently 12 h and 4 days after the last meal. The blood samples were analysed for the vitamin D metabolites 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D). All participants answered a semi-quantitative food-frequency questionnaire, which was used to estimate usual daily nutrient intake. The study was carried out in the last part of March 2001.
Results: The median daily vitamin D intake estimated from the questionnaire was 9.9 microg. The proportion of subjects with baseline 25(OH)D level below 50 nmol l(-1) was 15.4% and none were below 37.5 nmol l(-1). Only "mølje consumption" and "time spent in daylight" were significantly associated with baseline log 25(OH)D. The mean total intake of vitamin D in the three servings was 272 microg (standard deviation 94 microg), ranging from 142 to 434 microg. Relative to baseline plasma concentration, the mean level of 25(OH)D decreased slightly in both post-consumption samples (P< or =0.03), while 1,25(OH)2D peaked 12 h after the final meal (P=0.03).
Conclusion: Three mølje meals provided, on average, an amount of vitamin D equal to 54 times the recommended daily dose. Subjects with food consumption habits that included frequent mølje meals during the winter sustained satisfactory vitamin D levels in their blood, in spite of the long "vitamin D winter" (i.e. absence of ultraviolet-induced vitamin D production in the skin).