One vegetarian/vegan friendly caplet is all you need to meet your daily requirement of this essential vitamin. Vitamin C is a superior antioxidant, and one of the best-known nutrients for keeping your immune system healthy. Sundown Naturals High potency Vitamin C is an ideal complement to the immune and antioxidant system support. As one of the key vitamins for immune health, Vitamin C is important for the functioning of white blood cells which are essential components of the immune system, and contributes to heart health.