The two main types are vitamin D2 and vitamin D3. • Vitamin D2 (ergocalciferol) is produced by plants & fungi which are exposed to UV light i.e. mushrooms & yeast. • Vitamin D3 (cholecalciferol) is produced by the human body in response to sunlight and is also available through dietary sources, such as fish and algae. According to studies, D3 is 1.7 to 3 times more potent and has a longer-lasting effect than D2 in increasing serum 25-hydroxyvitamin D levels - the active form of vitamin D in humans. This is why we use D3 for all the vitamin D products in our range.