Explainer: What Are Antioxidants? | Science News for Students

Explainer: What Are Antioxidants?

Certain chemicals, including many in foods, protect the body from harmful chemical reactions
Mar 19, 2008 — 8:00 am EST
rainbow of carrots

Here’s a rainbow of carrots that U.S. scientists have developed to be both nutritious and a good source of natural antioxidants. 

Stephen Ausmus/USDA-ARS

Antioxidants are chemicals that may help fight damage due to disease and aging. These powerful compounds work by blocking oxidation. That’s a type of natural chemical reaction (often involving oxygen) that can harm cells.

The molecules that trigger oxidation are called, not surprisingly, oxidants. Chemists tend to also refer to these chemicals as free radicals (or sometimes just "radicals"). They are produced by nearly everything we do that involves oxygen, including breathing and digestion.

Free radicals aren't all bad. In fact, they perform important functions in the body. Among those good tasks: killing off old cells and germs. Free radicals become a problem only when we produce too many of them. Breathing in cigarette smoke and other types of air pollution often increases the body’s exposure to free radicals. So does aging.

To keep oxidation from harming healthy cells, many plants and animals (including people) produce antioxidants. However, organisms tend to make fewer of these helpful chemicals as they get old. That's one reason scientists suspect that oxidation is related to the types of chronic disease (heart ails, diabetes and more) seen in senior citizens. With fewer antioxidants to defend their bodies, oxidation can damage more and more of their cells.

Plants make hundreds of thousands of chemicals, also known as phytochemicals. Many thousands of these work as antioxidants in the human body. Scientists now think that eating a wide variety of plant-based foods containing these compounds can boost our own antioxidant defenses. This could keep people healthier and less likely to develop disease.

In fact, that's one reason why experts recommend that people eat many different kinds of fruits and vegetables. Which foods are richest in these chemicals? One easy clue is color. A number of the plant pigments are powerful natural antioxidants. And plant-based foods that are bright yellow, red, orange, purple and blue often contain good sources of these pigments.

Not all antioxidants are pigments, however. So the best policy is to eat plenty of plant-based foods every day. Below are some examples of potent antioxidants that can be found in various fruits and vegetables:

vitamin C(ascorbic acid) — oranges, tangerines, sweet peppers, strawberries, potatoes, broccoli, kiwi fruit

vitamin E— seeds, nuts, peanut butter, wheat germ, avocado

beta carotene(a form of Vitamin A) — carrots, sweet potatoes, broccoli, red peppers, apricots, cantaloupe, mangoes, pumpkin, spinach

anthocyanin— eggplant, grapes, berries

lycopene— tomatoes, pink grapefruit, watermelon

lutein— broccoli, brussels sprouts, spinach, kale, corn

Power Words

antioxidant     Any of many chemicals that can shut down oxidation, power and potentially damaging reactions. Many plant-based foods are good sources of natural antioxidants, including vitamins C and E.

chemical reaction     A process that involves rearrangement of the molecules or structure of a substance, as opposed to a change in physical form.

free radical  A charged molecule (typically highly reactive and short-lived) having one or more unpaired outer electrons. It will attempt to steal electrons to make itself whole again through a process known as oxidation.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

oxidation     A process that involves one molecule’s theft of an electron from another. The victim of that reaction is said to have been “reduced.” The theft victim makes itself whole again by robbing an electron from another molecule, triggering another case of oxidation. These chemical reactions are so violent, chemically, that they can easily kill cells.

oxygen    A gas that makes up about 21 percent of the atmosphere. All animals and many microorganisms need oxygen to fuel their metabolism.

phytochemical    From phyto, which is Greek for plant, the term refers to chemicals made by plants.

pigment  A material, like the natural colorings in paints and dyes, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. 

Further Reading

S. Ornes. “Explainer: How and why fires burn.” Science News for Students. March 14, 2014.

E. Sohn. “How super are superfruits?” Science News for Students. March 19, 2008.

S. Webb. “The color of health.” Science News for Students. Feb. 22, 2005.