There are a few different forms of vitamin D3 on the market, and it can be confusing to know which one to take. The best form of vitamin D3 to take is cholecalciferol, which is the type of vitamin D3 found in food sources like fish and eggs. Supplementing with cholecalciferol is the most effective way to raise your vitamin D levels, and it’s also the form that is least likely to cause side effects.