What is Doctor’s Best Vitamin C featuring Quali-C? Doctor’s Best Vitamin C featuring Quali-C promotes immune response, supports the cardiovascular system and is essential for joints and other connective tissues. Doctor’s Best uses Quali -C, a brand of ascorbic acid manufactured in Scotland that is prized for its quality and reliability. Ascorbic acid is invaluable to the body for its role as an electron donor, supporting numerous metabolic enzymes in addition to enhancing the body’s total antioxidant potential. It is essential for the synthesis of collagen, carnitine, and certain brain chemical transmitters. Clinical research confirms vitamin C\'s fundamental support for the brain, eyes, heart and circulation, immune system, and all the body\'s other organ systems. How it works? Vitamin C is a key compound in the body’s “antioxidant network,” a chain of synergistic, inextricability linked, well-studied antioxidants that includes glutathione (GSH) and vitamin E. When vitamin E neutralizes free radicals it needs to be renewed. Vitamin C can change this status, by regenerating vitamin E back to its native form, and is thought to “spare” glutathione in the body as well.Non-GMO, Gluten free, Soy free, Vegan.