When a cell with a damaged DNA strand divides, cell metabolism and duplication becomes deranged. Thus, a mutation can arise which in turn is an important factor in carcinogenesis. It is believed that antioxidants exert their protective effect by decreasing oxidative damage to DNA and by decreasing abnormal increases in cell division. Some research has indicated that people who smoke tend to have lower antioxidant levels than nonsmokers and are at an increased risk for both cancer and cardiovascular disease. The amounts of fruits and vegetables included in one's diet appears to have significant impact on cancer risk.
Antioxidant activity is believed to be responsible for much of the protection against tumorgenesis.
Because of its large surface area, the respiratory tract is major target for free radical insult, not to mention the fact that air pollution is a major source of respiratory distress. Recent studies suggest that free radicals may be involved in the development of pulmonary disorders such as asthma. Cellular damage caused by free radicals is thought to be partly responsible for the bronchial inflammation characteristic of this disease. It has been suggested that increasing antioxidant intake may help to reduce oxidant stress and help to prevent or minimize the development to asthmatic symptoms. Vitamin C, Vitamin E, and beta carotene supplementation have been associated with improved pulmonary function.