Optimal Vitamin D Liquid by Seeking Health provides a potent 50 mcg (2,000 IU) dose of vitamin D3 per drop, in pure olive oil base. Vitamin D is essential for the normal functioning of many important systems in the body and is needed to support a healthy immune system and long-term bone health. Many do not get sufficient vitamin D3 in their diet, and the synthetic vitamin D2 that is added to dairy products is not typically well-absorbed or included in sufficient amounts. Vitamin D3 occurs naturally in fatty fish, fish oil (especially cod liver oil), egg yolks, and beef liver. Optimal Vitamin D contains cholecalciferol derived from cholesterol in sheep’s wool, making it suitable for vegetarians.