Vitamin C is a water-soluble antioxidant and one of the best researched nutrients. Most mammals can produce vitamin C as they need it but the human system evolved without this ability so we must ensure an adequate daily intake to stay healthy. Vitamin C is found in fruits and vegetables, but it is easily destroyed by heat, cooking, processing, and storage, and rapidly eliminated from our system in the urine. Inadequate levels of vitamin C may be seen in cases of physical and mental stress, older people and those with chronic conditions including cardiovascular disease, asthma, arthritis, age-related eye disease, and certain cancers. Vitamin C is best known for strengthening the immune system by supporting and improving white blood cell function.