Antioxidant
An antioxidant is a chemical that prevent the oxidation of other chemicals. In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules: in some cases the body uses this to fight infection. In other cases, the damage may continue to the body's own cells. The presence of extremely easily oxidisable compounds in the system can "mop up" free radicals before they damage other essential molecules.
The following vitamins have shown positive antioxidant effects:
- Retinol (Vitamin A or beta-carotene) has been discovered to protect dark green, yellow and orange vegetables and fruits from solar radiation damage, and is thought to play a similar role in human body. Carrots, squash, broccoli, sweet potatoes, tomatoes, kale, collards, cantaloupe, peaches and apricots are particularly rich sources of beta-carotene.
- Ascorbic acid (Vitamin C) is a water-soluble compound that fulfills this role, among others, in living systems. Important sources include citrus fruits (like oranges, sweet lime, etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and tomatoes..
- Vitamin E (tocopherol) is fat soluble and similarly protects lipids. Sources include wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oil and fish-liver oil.
- Selenium is best obtained through foods, as large doses of the supplement form can be toxic. Good food sources include fish, shellfish, red meat, grains, eggs, chicken and garlic. Vegetables can also be a good source if grown in selenium-rich soils.
Several food additives (including ascorbic acid and tocopherol-derived compounds) are used as antioxidants to help guard against deterioration of food. (see: preservative)