Determinants of vitamin D status in pregnant fair-skinned women in Sweden.

Low maternal vitamin D status during pregnancy may have negative consequences for both mother and child. There are few studies of vitamin D status and its determinants in pregnant women living at northern latitudes. Thus, the present study investigates vitamin D status and its determinants during the third trimester of women living in Sweden (latitudes 57-58°N). A total of ninety-five fair-skinned pregnant women had blood taken between gestational weeks 35 and 37. The study included a 4 d food diary and questionnaires on dietary intake, supplement use, sun exposure, skin type, travels to southern latitudes and measure of BMI. Serum 25-hydroxyvitamin D (25(OH)D) was analysed using the chemiluminescence immunoassay. In the third trimester of pregnancy, mean serum concentration of 25(OH)D was 47.4 (sd 18.1) nmol/l (range 10-93 nmol/l). In total, 65% of women had serum 25(OH)D < 50 nmol/l and 17 % < 30 nmol/l. During the winter, 85% of the pregnant women had serum 25(OH)D < 50 nmol/l and 28 % < 30 nmol/l. The main determinants of vitamin D status were as follows: season; use of vitamin D supplements; travels to southern latitudes. Together, these explained 51% of the variation in 25(OH)D. In conclusion, during the winter, the majority of fair-skinned pregnant women had serum 25(OH)D < 50 nmol/l in their third trimester and more than every fourth woman < 30 nmol/l. Higher vitamin D intake may therefore be needed during the winter for fair-skinned pregnant women at northern latitudes to avoid vitamin D deficiency.