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 gr 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.