Vitamin D3 Liquid by Pure Encapsulations provides 1000 IU (25 ug) of vitamin D in the body's preferred form as D3. In liquid form, it is highly absorbable and easy to take. Vitamin D3 can be obtained from the sun during the summer months however, the sun in winter is not strong enough for us to produce it naturally. Having adequate vitamin D levels is important for a healthy immune system.