NOW combines three well known immune-enhancing ingredients in this high potency seasonal support product.* With the antioxidant and immune power of vitamin C plus the immune-supporting properties of vitamin D and zinc, this combination helps optimize the body's immune response to environmental challenges.* This product utilizes Albion™ Zinc Bisglycinate, a form of zinc that has been shown in clinical studies to have superior bioavailability compared to other forms of supplemental zinc.