Giving children extra vitamin D may cut their risk of developing Type 1 diabetes by 29%.
Around 250,000 people in the UK have Type 1 diabetes, which usually develops in childhood or adolescence and is unconnected to lifestyle factors such as obesity.
Of these people, at least 20,000 are currently school age.
A review of five studies, published online in the Archives of Disease in Childhood, found children given vitamin D supplements were almost a third less likely to develop the disease than those not given any.
The higher and the more regular the dose, the lower was the likelihood of developing the disease, it found.
However, it was unclear from the studies how old many of the children were or what the exact dose was.
The authors said levels of vitamin D and sunlight, from which the body manufactures the vitamin, have been implicated in the risks of developing other autoimmune disorders, including multiple sclerosis and rheumatoid arthritis.
They warned that the incidence of Type 1 diabetes is expected to rise worldwide, by 40% in 2010 based on 2000 figures.
Dr Victoria King, research manager of the charity, Diabetes UK, said: "This study suggests that taking vitamin D in childhood has the potential to prevent the development of Type 1 diabetes.
"However, much more research, in particular controlled trials which compares the results when one group of people are given vitamin D supplements and one group is not, are needed before we can confirm a concrete association between vitamin D and Type 1 diabetes."
