AIMS/HYPOTHESIS: To test whether cod liver oil or vitamin D supplements either taken by the mother during pregnancy or by the child in the first year of life is associated with lower risk of Type I (insulin-dependent) diabetes mellitus in children.

METHODS: We carried out a population-based case control study in Vest-Agder county of Norway, evaluating the use of supplements by a mailed questionnaire. We received responses from 85 diabetic subjects and 1,071 control subjects. Odds ratios (OR) with 95% confidence intervals (CI) were estimated using logistic regression analyses.

RESULTS: When mothers took cod liver oil during pregnancy their offspring had a lower risk of diabetes. The unadjusted OR was 0.30, 95% CI: (0.12 to 0.75), p = 0.01. This association changed very little and was still significant after adjusting for age, sex, breastfeeding and maternal education. Mothers taking multivitamin supplements during pregnancy [adjusted OR= 1.11, 95% CI: (0.69 to 1.77)], infants taking cod liver oil in the first year of life [adjusted OR = 0.82, 95 % CI: (0.47 to 1.42) and the use of other vitamin D supplements in the first year of life [adjusted OR = 1.27, 95 % CI: (0.70 to 2.31)] was not [corrected] significantly associated with the risk of diabetes.

CONCLUSION/INTERPRETATION: We found that cod liver oil taken during pregnancy was associated with reduced risk of Type I diabetes in the offspring. This suggests that vitamin D or the n-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid in the cod liver oil, or both, have a protective effect against Type I diabetes.