Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Damage due to free radicals damage may lead to cancer. Antioxidants interact with and stabilise free radicals and may prevent some of the damage free radicals otherwise might cause. Examples of antioxidants include beta-carotene, lycopene, vitamins C, E, and A, and other substances.

Fruits and vegetables provide a range of antioxidants, vitamins A, C and E, carotenoids and flavonoids. Fruits and vegetables that have comparatively high levels of antioxidants include apples, grapefruit, green grapes, oranges, peach, red plums, strawberries, beetroot, sprouts cauliflower, green cabbage, lettuce, onion, spinach and tomatoes. Antioxidants are abundant in other foods including nuts, grains and some meats, poultry and fish.

• Beta-carotene is found in many foods that are orange in colour, including sweet potatoes, carrots, apricots, pumpkin, and mangoes. Some green leafy vegetables including spinach, are also rich in beta-carotene
   
• Lutein, best known for its association with healthy eyes, is abundant in green, leafy vegetable, spinach etc.
   
• Lycopene is a potent antioxidant found in tomatoes, watermelon, guava, papaya, apricots, pink grapefruit, oranges, and other foods
   
• Selenium is a mineral, not an antioxidant nutrient. However, it is a component of antioxidant enzymes. The amount of selenium in soil, which varies by region, determines the amount of selenium in the foods grown in that soil. Animals that eat grains or plants grown in selenium-rich soil have higher levels of selenium in their muscle
   
• Vitamin A is found in three main forms: retinol (Vitamin A1), 3,4-didehydroretinol (Vitamin A2), and 3-hydroxy-retinol (Vitamin A3). Foods rich in vitamin A include liver, sweet potatoes, carrots, milk, egg yolks and mozzarella cheese
   
• Vitamin C is also called ascorbic acid, and can be found in high abundance in many fruits and vegetables and is also found in cereals, beef, poultry and fish
   
• Vitamin E, also known as alpha-tocopherol, is found in almonds, in many oils including wheat germ, safflower, corn and soybean oils, and also found in mangoes, nuts, broccoli and other foods

Antioxidants help to reduce the risk of cancer, heart attack and stroke.

Protection against heart disease:

Deficiencies in Vitamins A, C, E and beta carotene have been linked to heart disease. All of these nutrients have antioxidant effects and other properties that may benefit the heart.

• Vitamin E: eating foods rich in natural vitamin E may be protective. Vitamin E may prevent blood clots and the formation of fatty plaques and cell proliferation on the walls of the arteries
   
• Vitamin C: Vitamin C appears to maintain blood vessel flexibility and to improve circulation in the arteries
   
• Folate, Vitamin B6, and Vitamin B12. Several important studies have demonstrated a link between deficiencies in the B vitamins folate, B6, and B12 and elevated blood levels of homocysteine, an amino acid believed to be a risk factor for atherosclerosis. Both B12 and folate reduce homocysteine levels, and evidence is increasing that this effect may protect the heart.
   
• Vitamin B3. Niacin (vitamin B3) is used for lowering unhealthy cholesterol levels
   
• Carotenoids and heart protection: a high intake of fruits and vegetables containing beta carotene, lycopene, and other carotenoids may reduce the risk of heart attack
   
• Phytochemicals and heart protection: Flavonoids, particularly those found in both black and green tea, onions, red wine or red grape juice, and apples, may protect against damage done by cholesterol and help prevent blood clots

Vitamin C. There is a lower risk for stroke in subjects with the highest blood levels of vitamin C. Studies have found protection in foods rich in vitamin C, although supplements do not appear to offer any advantage.
 

B Vitamins: Vitamins B6, B12, and folate are important for the production of neurotransmitters, the chemical messengers in the brain that regulate mood and concentration. Deficiencies in these vitamins have been observed in people with depression and dementia. People who have higher blood levels of folic acid have a lower than average risk for stroke
 

Carotenoids and stroke protection: Studies have reported a lower risk of stroke from carotenoids, including beta carotene and lycopene.

Many fresh fruits and vegetables contain chemicals that may fight many cancers, including lung, breast, colon, and prostate cancers. Examples of important cancer-fighting foods include the following:

• Cruciferous vegetables (e.g., cabbage, sprouts, broccoli)
   
• Tomatoes (which contain lycopene)
   
• Carrots (which contain alpha and beta carotene)

There is some evidence that antioxidants may enhance the anticancer effects of chemotherapy. Antioxidant nutrients that may have properties that may help reduce the side effects of chemotherapy include vitamins E and C, beta carotene, isoflavones found in soy, and quercetin (found in red wine and purple grape juice).

Although supplements of vitamins A, C, and E appear to have no advantages, studies have reported an association between low blood levels of these antioxidant vitamins and a higher risk for cancer.

• Vitamin D. Some studies have suggested that certain vitamin D compounds may inhibit certain cancer cells, specifically prostate cancer, from proliferating.
   
• Folate and B12. These B vitamins helps prevent cells from becoming malignant. Folic acid supplements may provide some protection against cervical and colon cancer and may reduce the risk for breast cancer among women who regularly drink alcohol
   
• Carotenoids and cancer protection. A number of studies have reported that fruits and vegetables rich in carotenoids are associated with protection against many cancers. Lycopene, found in tomatoes, may have particular value in protection against prostate, colon, lung, and bladder cancer.