Vitamin C (L-ascorbic acid) is a water-soluble, essential nutrient that is involved in many complex functions in the body, including neurotransmitter, collagen, carnitine and tyrosine synthesis, and catabolism. Vitamin C is also a potent antioxidant, protecting healthy cells throughout the body, but especially in the lungs. Humans are among the few mammals unable to synthesize vitamin C, so it must be obtained from the diet. Dietary sources high in vitamin C include orange juice, strawberries, fortified cereals and most citrus fruits