For various reasons, vitamin D deficiency is a persistent problem among many populations. Dietary guidelines cannot currently address the nutritional deficit, as foods naturally rich in vitamin D are few, infrequently consumed and may not be widely available, and fortified foods are unevenly supplied. Supplementation can be a useful approach for individuals to boost vitamin D intakes, but poor compliance makes it ineffective at a population level. Therefore, due to the persistent low supply of vitamin D in the food system, deficiency remains common. Many investigators have shown that increasing vitamin D in food through fortification of manufactured products and /or biofortification of animal foods is safe, as there is a wide gap between the dietary requirements for vitamin D intakes and the upper intake levels, which have generous safety margins, and effective, in terms of increasing vitamin D status. Vitamin D fortification has been proposed as a low-risk approach to vitamin D deficiency prevention that would have immediate benefits for increasing intakes and year-round vitamin D status in the population, with consequent long-term benefits for health promotion and disease prevention. A handful of governments around the world have implemented successful mandatory vitamin D fortification policies, but these are in the minority, and residual concerns around safety, implementation and monitoring hamper progress in most regions. Insufficient co-operation between scientists and the public, policy makers and industry could partly explain the failure to translate scientific and technical knowledge in vitamin D fortification into effective public health policy. The caution exhibited by National agencies to progress vitamin D fortification might be understandable given persistent doubt driven by gaps in the data available, particularly around safety across the life course. While many randomized controlled trials of food fortification with vitamin D have been conducted, the scale of these studies has been mostly limited and not always reflective of the diversity of the population. This talk will summarise the state of the art, consider gaps in the evidence base and propose an approach to co-designing nutrition policy for prevention of vitamin D deficiency.