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, therefore 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 and age-related eye disease. Vitamin C is best known for strengthening the immune system by supporting and improving white blood cell function. It is also essential for the proper formation of collagen, the building block of many tissues and a crucial component in skin rejuvenation. Vitamin C also helps to reduce histamine release in the body, thereby alleviating allergy symptoms. There are numerous forms of vitamin C with ascorbic acid being the most basic. People wanting a clinically proven form that is easier on the system than ascorbic acid may choose a form like Ester-C® brand calcium ascorbate.