The most well-known source of vitamin D3 is sunlight, there are a few food sources which are also naturally high in vitamin D3, these include;
Fatty fish and fish oils – Such as trout, sardines, salmon and mackerel
Red meat – Particularly offal, rather than muscle meat
Egg yolks – Contain most of the fats and vitamins of the egg, a single yolk can contain up to 37 IU of vitamin D
Vegetables – Sunlight exposed mushrooms include good levels of vitamin D, other vegetarian or vegan foods include soy products such as tofu and soy milk.