Vitamin D is synthesized in the skin following UVB exposure.
Plant foods contain vitamin D2 (ergocalciferol) which must be converted into the active form to be used by the body. Unfortunately, this conversion rate is not always reliable or efficient. Animal foods contain vitamin D3, which is metabolized more efficiently as D3 than D2.
Plant Sources: Vitamin D2 is found in small amounts in mushrooms (about 15-20 IU/cup).
Animal Sources: Vitamin D3 is found in cod liver oil (400 IU/tsp), salmon (450 IU/3 oz.), mackerel (500 IU/3 oz.), sardines (25 IU each), and egg yolk (40 IU/yolk). These sources are much richer and already contain the active form. However, they are unavailable to those following a vegan or vegetarian diet.
There are a wide range of supplements available, but many contain the less absorbable form of D2, or fail to include the necessary cofactors or “helper nutrients” needed for the body to properly absorb and use vitamin D. D3+K2 Complex combines vegan sources of vitamin D3 and vitamin K2 along with fermented K1, plus an organic food complex of shiitake mushroom mycelia, camu camu berry, collard greens, spinach, parsley, and cruciferous sprouts.