Type I diabetes is an autoimmune disorder characterised by destruction of the β-cells of the pancreas during early childhood. There is a known genetic component to the disease (genes in the HLA complex of chromosome 6p21) but the genetic component is not enough to trigger the disorder. However, the environmental factors that contribute to the disease are not fully understood. Evidence suggests that vitamin D insufficiency plays some role in the development of type I diabetes, but its mechanisms are unclear. The long chain fatty acids in fish are potent anti-inflammatory agents and as such may be protective of type I diabetes, especially because prostaglandin metabolism in children with type I diabetes may be dysfunctional. Cod liver oil contains both vitamin D and long chain fatty acids and so shows promise as an effective nutrients formula in the prevention of type I diabetes.
Researchers1 have investigated the effects of cod liver oil supplementation in the first year of infant life on the risk of developing type I diabetes. In Norway, 545 infants with type I diabetes and 1668 non-diabetic infants were contacted and a frequent food questionnaire was used to assess the dietary supplements consumed by the infant in the first year of life and by the mother during pregnancy. The results showed that infants who were fed cod liver oil during the first year of life had a significantly lower risk of type I diabetes (adjusted odds ratio: 0.74). However, the use of other vitamin D supplements and supplementation of the mother during pregnancy with cod liver oil or vitamin D was not associated with type I diabetes. Therefore cod liver oil my protect infants from developing type I diabetes if taken within the first year of life.
Because the researchers did not take blood samples of the subjects it is difficult to draw conclusions from the lack of effect of vitamin D, based on the fact that vitamin D intake has shown inverse association with type I diabetes in other studies. However, it could be hypothesised that the supplements were simply not of a high enough dose to raise plasma levels of 25-hydroxyvitamin D sufficiently. In addition, the researchers ignored those who started taking supplements at 13 months of age, despite evidence that 12 months of age roughly corresponds to the time of onset of type I diabetes pathogenesis. Because the cod liver oil was protective of type I diabetes, but vitamin D supplements were not, it might be concluded that the long chain fatty acids in fish reduce diabetes risk, possibly through the regulation of pro-inflammatory series 2 prostaglandins.
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