Vitamin D in the prevention of type 1 diabetes: would increasing food fortification reduce the incidence?

This paper reviews data regarding the role of vitamin D in the genesis of type 1 diabetes (T1DM) and considers the hypothesis that vitamin D deficiency increases the incidence rate of T1DM. Vitamin D has actions on immune cells that would suppress autoimmunity with preservation of anti- infective actions. Geographical latitude and both season of diagnosis and of birth affect case numbers, most likely via the effect of UVB sunlight on vitamin D synthesis. Other factors, such as seasonal viral infections, may be important. Serum concentrations of 25(OH) vitamin D have mostly been found to be lower with diagnosis of T1DM. Vitamin D deficiency is common, particularly in the UK. From data on vitamin D concentrations in non-diabetic controls in mostly southerly nations this review estimates the population mean serum 25(OH)D concentration associated with low T1DM incidence to be >80 nmol/l. Achieving this in Britain would require supplementing current intake with 1500-2000 IU vitamin D daily. Increased food fortification would be the most effective method. An estimate based on the limited data available suggests this might generate a 25-30% reduction in the incidence of T1DM.