Presented by Alexis Lieberman, M.D.

Fairmount Pediatrics and Adolescent Medicine

What are Free Radicals?

A byproduct of cellular metabolism are free radicals. These are molecules with only one electron, not two. The most common form of free radical is oxygen with only one electron, not with two electrons that are bonded together which is the normal form of oxygen.

Free radicals scavenge for other molecules to bond with. In the process, they damage cells. They can destroy cellular compounds and damage proteins, lipids, and DNA, and lead to cell death – especially in the brain which generates more oxidative by products than other organs of the body. This process is called oxidative stress.

What kind of damage can be done by free radicals?

The following diseases are caused or aggravated by free radicals:

  • Alcoholic liver and heart conditions
  • Arteriosclerosis
  • Arthritis
  • Autoimmune diseases
  • Cancer
  • Cataracts
  • Circulation disturbances
  • Coronary heart disease
  • Diabetes
  • Emphysema of the lung
  • Inflammatory reactions
  • Liver Cirrhosis
  • Malaria
  • Multiple Sclerosis (MS)
  • Neuronal Lipofuscinosis
  • Parkinson’s Disease
  • Porphyria
  • Premature Ageing
  • Retinal Diseases
  • Rheumatoid diseases
  • Senile Dementia
  • Side-effects of medicines

What are antioxidants?

Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals might otherwise cause.

What are examples of antioxidants?

L-Carnosine   L-Carnosine is a multi-potent super-antioxidant which stabilizes and protects the cell membrane. Specifically, as a water-soluble free radical scavenger it prevents lipid peroxidation within the cell membrane.
Carotenoids/  Beta-carotene Carotenoids are perhaps best known for their ability to be converted to vitamin A, which is essential for healthy vision and reproduction, and for maintaining body tissues. Carotenoids are also powerful antioxidants on their own right.They are found in many foods that are orange in color, including sweet potatoes, carrots, cantaloupe, squash, apricots, pumpkin, and mangos. Some green, leafy vegetables, including collard greens, spinach, and kale, are also rich in beta-carotene.
Co-Enzyme Q10 Co Q10 is involved in the body’s metabolic processes, particularly in the release of energy from food, and is a potent antioxidant.
  Lutein Lycopene best known for its association with healthy eyes, is abundant in green, leafy vegetables such as collard greens, spinach, and kale.A potent antioxidant found in tomatoes, watermelon, guava, papaya, apricots, pink grapefruit, blood oranges, and other foods. Estimates suggest 85 percent of American dietary intake of lycopene comes from tomatoes and tomato products.
Vitamin A A fat-soluble vitamin involved in the formation and maintenance of healthy skin, hair, and mucous membranes. Vitamin A helps us to see in dim light and is necessary for proper bone growth, tooth development, and fertility and has been well documented for decades. It is also an important antioxidant. 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 B It has been recently discovered that several of the B vitamins have antioxidant effects and that they stimulate the activity of the immune system.
Vitamin C Vitamin C is an important antioxidant, and is also part of the cellular chemistry that provides energy and for making the collagen protein involved in the building and health of cartilage, joints, skin, and blood vessels. 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 Alpha-tocopherol is the most active form of vitamin E in humans, and is a powerful biological antioxidant. Vitamin E, also known as alpha-tocopherol, is found in almonds, in many oils including wheat germ, safflower, corn, and soybean oils, and is also found in mangos, nuts, broccoli, and other foods.
Selenium Selenium is a mineral, not an antioxidant nutrient. However, it is a component of antioxidant enzymes. Plant foods like rice and wheat are the major dietary sources of selenium in most countries. 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. In the United States, meats and bread are common sources of dietary selenium. Brazil nuts also contain large quantities of selenium.
Zinc Zinc is vital to about 200 different enzymes, to the formation of bone tissue, in the healing of wounds and sores, to the production of proteins, the regulation of ribosomal, ribonucleic acid synthesis and insulin and in the carbohydrate metabolism. Zinc is also an antioxidant.

Can antioxidants prevent cancer?

Considerable laboratory evidence from chemical, cell culture, and animal studies indicates that antioxidants may slow or possibly prevent the development of cancer. However, information from recent clinical trials is less clear. In recent years, large-scale, randomized clinical trials reached inconsistent conclusions.

How might antioxidants prevent cancer?

Antioxidants neutralize free radicals as the natural by-product of normal cell processes. Free radicals are molecules with incomplete electron shells which make them more chemically reactive than those with complete electron shells. Exposure to various environmental factors, including tobacco smoke and radiation, can also lead to free radical formation. In humans, the most common form of free radicals is oxygen. When an oxygen molecule (O2) becomes electrically charged or “radicalized” it tries to steal electrons from other molecules, causing damage to the DNA and other molecules. Over time, such damage may become irreversible and lead to disease including cancer. Antioxidants are often described as “mopping up” free radicals, meaning they neutralize the electrical charge and prevent the free radical from taking electrons from other molecules.

What does research show about how antioxidants help promote health?

  • Studies have linked dietary antioxidants and asthma incidence/severity
  • Subjects with a high exposure to oxidative air pollutants have shown short-term protective effects of antioxidants on lung function
  • Antioxidant supplementation (50 mg/d of vitamin E and 250 mg/d of vitamin C) might modulate the impact of ozone exposure on the small airways of children with moderate to severe asthma living in Mexico City
  • Observational studies suggest a role of a healthy antioxidant diet for the prevention of coronary heart disease and cancer
  • A number of observational studies in adults have found an association between low fruit intake and asthma or lower lung function
  • Eating apples twice or more in a week, compared with eating them less than once a month, was negatively associated with wheezing
  • Intake of bananas, but not other fruits, was negatively associated with wheeze. Bananas have a higher content of water soluble phenolic acids than other fruits, including apples, and could plausibly reduce asthma inflammation. Furthermore, bananas have been shown to increase the absorption of other nutrients and are rich in pro-vitamin A carotenoids.
  • Vitamin C has been shown in several case-control and cross-sectional studies to be associated with a reduced risk of asthma, but in the only available substantive longitudinal study, vitamin C intake had no effect on asthma incidence.
  • One report suggesting protection by flavones against markers of COPD
  • Fatty acid effects: Intake of omega-3 polyunsaturated fatty acids from fish oils, which is potentially beneficial, while omega-6 and trans-fatty acids, which may be detrimental to asthma
  • 18 737 children aged 6-7 years living in Italy. Intake of citrus fruit or kiwi fruit was a highly significant protective factor for wheeze in the last 12 months
  • 598 Dutch children aged 8–13 years. Our findings suggest that a high intake of whole grain products and fish may have a protective effect against asthma in children.

Which foods are rich in antioxidants?

Antioxidants are abundant in fruits and vegetables, as well as in other foods including nuts, grains, and some meats, poultry, and fish.

The highest ranked foods in four major categories are as follows:

Fruits: blueberries, cranberries, and blackberries.

Vegetables: beans, artichoke hearts, and surprisingly, russet potatoes.

Nuts: pecans, walnuts, and hazelnuts.

Spices: cinnamon, oregano, and ground cloves.

Here’s the list of the top 20 food sources of antioxidants, based on their total antioxidant capacity per serving size:



Food item


Serving size
Total antioxidant capacity per serving size
1 Small Red Bean (dried) Half cup 13727
2 Wild blueberry 1 cup 13427
3 Red kidney bean (dried) Half cup 13259
4 Pinto bean Half cup 11864
5 Blueberry (cultivated) 1 cup 9019
6 Cranberry 1 cup (whole) 8983
7 Artichoke (cooked) 1 cup (hearts) 7904
8 Blackberry 1 cup 7701
9 Dried Prune Half cup 7291
10 Raspberry 1 cup 6058
11 Strawberry 1 cup 5938
12 Red Delicious apple One 5900
13 Granny Smith apple One 5381
14 Pecan 1 ounce 5095
15 Sweet cherry 1 cup 4873
16 Black plum One 4844
17 Russet potato (cooked) One 4649
18 Black bean (dried) Half cup 4181
19 Plum One 4118
20 Gala apple One 3903

While some foods are high in antioxidants, they may not be well-absorbed. Researchers also found that cooking method also had a significant effect on the antioxidant content of the foods tested, but those effects were not consistent.

For example, cooked Russet and red potatoes had much lower antioxidant levels than those found in raw potatoes. Boiling also decreased antioxidant levels in carrots, but cooking tomatoes increased their antioxidant content.

Here’s another listing, by antioxidant ORAC test results (another method of measuring antioxidant strength):

Goji BerriesDark chocolate 25,30013,120
Milk chocolate 6,740
Prunes 5,770
Raisins 2,830
Blueberries 2,400
Blackberries 2,036
Kale 1,770
Strawberries 1,540
Spinach 1,260
Raspberries 1,220
Brussels sprouts 980
Plums 949
Alfalfa sprouts 930
Broccoli 890


REFERENCES:Tricia M. McKeever and John Britton, Pulmonary Perspective, Diet and Asthma American Journal of Respiratory and Critical Care Medicine Vol 170. pp. 725-729, (2004)

B. J. Okoko, P. G. Burney, R. B. Newson, J. F. Potts and S. O. Shaheen, Childhood asthma and fruit consumption

Eunyoung Cho, ScD; Johanna M. Seddon, MD; Bernard Rosner, PhD; Walter C. Willett, MD, DrPH; Susan E. Hankinson, ScD , Prospective Study of Intake of Fruits, Vegetables, Vitamins, and Carotenoids and Risk of Age-Related Maculopathy Arch Ophthalmol. 2004;122:883-892.

National Cancer Institute fact sheet on antioxidants