Most studies have concentrated on investigating the effect of vitamin D exposure in infancy. Although infancy is thought to be potentially a crucial period for the development of type 1 diabetes, studies have focused on this stage of life mostly because vitamin D intake of the infant is (relatively) easily measurable.

Results have been relatively consistent. In a Norwegian study, mother’s cod liver oil consumption during pregnancy was observed to be associated with a reduced risk of type 1 diabetes in the offspring. In another case-control study, carried out in 7 European countries, diabetes risk was found to be reduced by 30% if the child had received vitamin D supplementation. In the Northern Finland 1966 Cohort study, we found also an association between vitamin D and reduced diabetes risk , and I will talk about this study in more detail next.

To my knowledge, there is practically no published data on the effect of vitamin D intake or status after infancy, before the onset of the disease.