Limited data from human observational studies suggest that early supplementation with 10 microg/d (400 IU/d) or less of vitamin D may not reduce the risk for type 1 diabetes but that doses of 50 microg/d (2000 IU/d) and higher may have a strong protective effect. Current U.S. recommendations (5-25 microg/d, 200-1000 IU/d) fall in the largely unstudied dose range in between. All infants and children should receive between 5 microg/d and 25 microg/d of supplemental vitamin D, particularly if they have limited sun exposure, live in northern areas, are exclusively breastfed, or are dark skinned. Caretakers of infants and children at increased risk of type 1 diabetes might wish to consider supplementation toward the upper end of that range or above. Additional studies are needed that 1) investigate the association between 25-hydroxyvitamin D and autoantibodies predictive of type 1 diabetes in infancy and beyond, 2) test the ability of vitamin D supplement doses between 5 and 50 microg/d to prevent autoantibodies and/or type 1 diabetes in infancy and beyond, and 3) examine the safety of vitamin D intakes of 25 microg/d and higher. Also, we need to consider the possible benefits of vitamin D supplementation when deciding whether or not to screen children for type 1 diabetes risk and to add type 1 diabetes to the growing list of outcomes that are considered when vitamin D recommendations are next revised.