New perspectives on vitamin D food fortification based on a modeling of 25(OH)D concentrations

Background: In Germany, vitamin D intake from food and synthesis in the skin is low, which leads to low 25(OH)D serum concentrations. In contrast to many other countries, general vitamin D food fortification is still prohibited in Germany, although the European Commission published a regulatory framework to harmonize addition of vitamins to foods. Thus the purpose of our study was to develop a vitamin D fortification model, taking into account all vitamin D sources with the goal to fulfill requirements of intake recommendations or preferable 25(OH)D serum concentrations. Finally, the aim was to assess the suitability of different carriers and associated risks. Methods: We developed a mathematical bottom-up model of 25(OH)D serum concentrations based on data about vitamin D sources of the German population such as sunlight, food and supplements for all federal states taking seasonal and geographical variations into account. We used this model to calculate the optimal fortification levels of different vitamin D carriers in two approaches. First we calculated required fortification levels based on fixed intake recommendations from e. g. the IOM or the DGE and second based on achieving certain 25(OH)D serum concentrations. Results: To lift 25(OH)D serum concentration in Germany to 75 nmol/L, e.g. 100 g bread has to be fortified with 11.3 mu g during winter, resulting in a daily vitamin D intake of 23.7 mu g. Bread seems to be a suitable carrier for base supply. However, overdose risk with a single fortified product is higher than the risk with several fortified carriers. Conclusions: With the model in hand, it is possible to conceive vitamin D fortification strategies for different foodstuffs and model its impact on 25(OH) D serum concentrations.