Getting sufficient vitamin D from food alone is very difficult. Very few foods are a good source of vitamin D. In addition to our own production, vitamin D3 only occurs in animal products . The best sources of vitamin D3 are oily fish such as mackerel, herring and salmon. But these quantities are very low: it takes 100 g of wild salmon to ingest just 20 micrograms of vitamin D3. Vitamin D2 is vegetable vitamin D that occurs in small concentrations in certain types of mushrooms .