BACKGROUND: A recent study showed that nulliparous women who develop preeclampsia had low concentrations of vitamin D in serum sampled in midpregnancy. The aim of the present study was to estimate the association between intake of vitamin D during pregnancy and the risk of preeclampsia in 23,423 nulliparous pregnant women taking part in the Norwegian Mother and Child Cohort Study.

METHODS: Participating women answered questionnaires at gestational week 15 (general health questionnaire), at week 22 (food frequency questionnaire), and at week 30 (general health questionnaire). Pregnancy outcomes were obtained from the Medical Birth Registry. Nutrient intake was calculated from foods and dietary supplements. We estimated relative risks as odds ratios, and controlled for confounding with multiple logistic regression.

RESULTS: The odds ratio of preeclampsia for women with a total vitamin D intake of 15-20 microg/d compared with less than 5 microg/d was 0.76 (95% confidence interval = 0.60-0.95). Considering only the intake of vitamin D from supplements, we found a 27% reduction in risk of preeclampsia (OR = 0.73 [0.58-0.92]) for women taking 10-15 microg/d as compared with no supplements. No association was found between intake of vitamin D from the diet alone and the occurrence of preeclampsia.

CONCLUSIONS: These findings are consistent with other reports of a protective effect of vitamin D on preeclampsia development. However, because vitamin D intake is highly correlated with the intake of long chain n-3 fatty acids in the Norwegian diet, further research is needed to disentangle the separate effects of these nutrients.