What Are Antioxidants? Benefits, Sources & How They Work

Written by Jaclyn Weiner, RD, RDN, MEd, MS

Medically reviewed by Dr. Mehrosh Ahmer MBBS

Last reviewed October 28, 2026

Antioxidants are substances that help protect your cells from damage caused by unstable molecules called free radicals. You’ll find them in many foods, especially fruits, vegetables, nuts, and whole grains. Your body also makes some antioxidants on its own.

Antioxidants get a lot of attention in health and wellness marketing. Some of that attention is deserved. But the full picture is more nuanced than “more antioxidants equals better health.”

This article explains what antioxidants are and how they work. It also covers where to find them, what the evidence does and doesn’t support, and why food sources and supplements aren’t interchangeable.

Important: This article is for general information only. It is not a substitute for professional medical advice. Talk with your healthcare provider before starting any new supplement.

What Are Antioxidants?

Antioxidants are substances that may prevent or delay some types of cell damage (NCCIH). Your cells produce highly reactive, oxygen-containing molecules during normal processes. Exposures such as pollution and cigarette smoke add to this. When these molecules build up faster than your body can manage them, the result is called oxidative stress (Frontiers in Chemistry, 2024).

Your body has its own defense and repair systems to help regulate this process. These include antioxidant enzymes that your body makes. Plant compounds with antioxidant activity, commonly found in food, may also support these pathways. For more detail, see CollectedMed’s overview of antioxidants and your health.

What Is Oxidative Stress?

Oxidative stress is an imbalance between free radicals and antioxidants in the body. It leads to cell damage (Cleveland Clinic).

Free radicals aren’t inherently bad. In small, normal amounts they serve useful functions, including cell signaling (Frontiers in Chemistry, 2024). Free radicals also form naturally when you exercise and when your body turns food into energy (NCCIH). Problems arise when production outpaces your body’s antioxidant defenses.

Several factors are associated with increased oxidative stress:

• Cigarette smoke and tobacco use (Cleveland Clinic)
• Air pollution (Cleveland Clinic)
• Excessive alcohol intake (Cleveland Clinic)
• High blood sugar levels (Frontiers in Molecular Biosciences, 2025)
• Certain toxin exposures
• Intense, prolonged physical exertion without adequate recovery

Over time, oxidative stress has been linked to several chronic conditions. These include cardiovascular disease, diabetes, and cancer (Marrocco et al., 2017). This is one reason antioxidants attract so much research interest. A link is not proof of cause, however.

How Do Antioxidants Work?

Antioxidants neutralize free radicals. They do this by donating an electron to the unstable molecule. This stabilizes it before it can damage cellular components such as DNA, proteins, or fats.

This is a normal, ongoing process in a healthy body. It doesn’t only start when you eat a particular food.

Different antioxidants work in different ways and in different parts of the body. This is one reason researchers emphasize a varied diet rather than reliance on a single compound.

Common Types of Antioxidants

Some of the most well-studied antioxidants include:

• Vitamin C: citrus fruits, peppers, strawberries, and broccoli (see foods high in vitamin C)
• Vitamin E: nuts, seeds, and vegetable oils
• Beta-carotene: a carotenoid in carrots, sweet potatoes, and dark leafy greens
• Selenium: a mineral in Brazil nuts, fish, and whole grains
• Flavonoids and other polyphenols: plant compounds in berries, tea, and cocoa
• Lycopene: tomatoes and watermelon
• Lutein: leafy greens such as spinach and kale
• Coenzyme Q10: made by the body and found in small amounts in meat and fish

The National Center for Complementary and Integrative Health (NCCIH) lists examples of antioxidants. They include anthocyanins, beta-carotene, catechins, coenzyme Q10, flavonoids, lipoic acid, lutein, lycopene, selenium, and vitamins C and E. These compounds are available in foods and as dietary supplements (NCCIH).

Food Sources of Antioxidants

Whole foods are the best-documented way to get antioxidants. Vegetables and fruits are rich sources, and NCCIH notes that concerns have not been raised about the safety of antioxidants in food (NCCIH). Foods also deliver many antioxidant compounds together, along with fiber, healthy fats, and other nutrients. For a longer list, see CollectedMed’s guide to antioxidant-rich foods.

Fruits and Vegetables

Brightly colored produce tends to be rich in antioxidants:

• Berries (see blueberries’ health benefits)
• Citrus fruits
• Tomatoes
• Carrots and sweet potatoes
• Leafy greens such as spinach and kale
• Bell peppers
• Broccoli and other cruciferous vegetables

The Dietary Guidelines for Americans, 2025-2030 call for about three servings of vegetables and two of fruit per day on a 2,000-calorie pattern. CollectedMed’s guide to the healthiest foods to eat every day covers many of these in more depth. To eat more produce, see how to eat more vegetables.

Nuts, Seeds, and Whole Grains

• Almonds and walnuts
• Sunflower seeds
• Brazil nuts (a notable source of selenium)
• Whole grains

Brazil nuts are very high in selenium. A single nut can contain roughly 68 to 91 micrograms. Adults need about 55 micrograms a day, and the upper limit is 400 micrograms from all sources (NIH Office of Dietary Supplements). A small portion is enough.

Other Sources

• Green and black tea (see green tea health benefits)
• Dark chocolate and cocoa
• Extra virgin olive oil
• Legumes, including beans and lentils

A Mediterranean-style diet emphasizes many of these foods together. The American Heart Association describes it as a dietary pattern that can help people meet a healthy eating pattern (AHA).

Potential Health Benefits of Antioxidants

Precision matters here, because marketing often overstates the science. Decades of dietary research suggest that foods rich in antioxidants, such as many vegetables and fruits, may help protect against chronic diseases like heart disease and cancer (NCCIH).

However, this kind of evidence shows an association. It doesn’t prove that antioxidants themselves cause the benefit. People who eat more produce often have other healthy habits too.

With that caveat, antioxidant-rich eating patterns are associated with:

• Supporting heart health (see heart-healthy foods)
• Supporting overall cellular health by helping manage oxidative stress
• Complementing an anti-inflammatory way of eating
• Contributing to a balanced diet rich in fruits, vegetables, and whole grains

Do Antioxidant Supplements Work?

This is the most important question to get right. The evidence for supplements differs from the evidence for food.

Large, long-term clinical trials have tested antioxidant supplements. They looked at whether supplements could prevent diseases such as cardiovascular disease and cancer. In most cases, the supplements did not reduce disease risk (NCCIH).

More specifically:

• Beta-carotene: High-dose beta-carotene supplements have been linked to a higher risk of lung cancer in people who smoke (NCCIH).
• Cochrane review: A systematic review of 78 randomized trials found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seemed to increase mortality, and higher doses of vitamin A might too (Bjelakovic et al., Cochrane).
• USPSTF 2022: The U.S. Preventive Services Task Force recommends against beta-carotene or vitamin E supplements to prevent cardiovascular disease or cancer. For other single or paired nutrients, it found the evidence insufficient to make a recommendation (USPSTF). This applies to community-dwelling, nonpregnant adults without known nutritional deficiencies.

Why Don’t Supplements Match Food?

Researchers have proposed a few explanations:

• Dosing: Supplements often deliver far more of a single antioxidant than food does. Large amounts may interfere with normal cell signaling and the body’s own defenses.
• Isolation: One antioxidant taken alone may not behave as it does in a whole food, alongside many other compounds.
• Confounding: People who eat the most produce often have other healthy habits. These include more physical activity, less smoking, and better sleep. Such habits may explain some of the benefit attributed to antioxidants.

The bottom line is this. Eating antioxidant-rich foods is well supported. Taking high-dose antioxidant supplements to prevent disease is not, and in some cases it may carry real risk.

Antioxidants and Specific Health Areas

Antioxidants and Heart Health

A diet rich in antioxidant foods is part of broader patterns, such as the Mediterranean diet. These patterns are associated with better cardiovascular health (AHA). Related topics include cholesterol and heart health and omega-3 fatty acids, which are often found in similar foods.

Antioxidants and Blood Sugar

Chronically high blood sugar is associated with increased oxidative stress (Frontiers in Molecular Biosciences, 2025). That is one reason nutrient-dense, antioxidant-rich eating is often discussed alongside efforts to prevent diabetes and support healthy blood sugar levels.

Antioxidants and Exercise

Intense, prolonged exercise without adequate recovery can contribute to oxidative stress. This doesn’t mean exercise is harmful. Active people generally live longer and have less risk of serious problems such as heart disease and type 2 diabetes (CDC). The benefits of exercise outweigh this concern for almost everyone.

A balanced approach pairs antioxidant-rich foods with regular activity and proper rest days.

Should You Take Antioxidant Supplements?

For most people who eat a varied diet, supplements are probably not necessary. They are also not automatically safe just because the compound occurs naturally in food.

Consider these points before starting any antioxidant supplement:

• Talk with your healthcare provider first. This matters most if you smoke, have a chronic condition, or take other medications.
• High-dose supplements are not the same as the antioxidants naturally found in food.
• Some antioxidant supplements may interact with medications, including certain blood thinners and cancer treatments. People in cancer treatment should talk with their care team first (NCCIH).
• More is not automatically better. In specific cases, such as beta-carotene in smokers, high doses may be harmful (USPSTF).

If you want to support your antioxidant intake, food is the strategy with the strongest evidence.

How to Get More Antioxidants From Your Diet

A few practical steps:

1. Eat a variety of colorful fruits and vegetables. Different colors generally reflect different antioxidant compounds. Variety matters more than any single “superfood.”
2. Choose whole foods over isolated extracts. Whole foods supply antioxidants together with fiber and other nutrients.
3. Include nuts and seeds regularly, as part of a broader healthy diet.
4. Consider a Mediterranean-style eating pattern, which naturally emphasizes many antioxidant-rich foods (AHA).
5. Limit habits that increase oxidative stress, such as smoking and excessive alcohol intake (Cleveland Clinic). Do this alongside eating well, not instead of it.

For a wider framework, see what is a healthy diet.

Frequently Asked Questions

What do antioxidants actually do in the body?

Antioxidants help neutralize free radicals. These are unstable molecules that can damage cells, proteins, and DNA when they build up faster than the body can manage them. This helps regulate oxidative stress (Cleveland Clinic).

What foods are highest in antioxidants?

Berries, leafy greens, citrus fruits, tomatoes, nuts, green tea, and extra virgin olive oil are commonly cited as antioxidant-rich. NCCIH identifies vegetables and fruits as rich sources (NCCIH). See antioxidant-rich foods for more.

Are antioxidant supplements safe?

Not automatically. Antioxidants from food are generally well tolerated. High-dose supplements are different. Beta-carotene in smokers has been linked to increased lung cancer risk in clinical trials (NCCIH). Talk with a healthcare provider before starting any antioxidant supplement.

Can antioxidants prevent cancer?

Current evidence does not support antioxidant supplements for cancer prevention (USPSTF). Some, like high-dose beta-carotene, may raise risk in smokers (NCCIH). Eating antioxidant-rich foods as part of a healthy diet is a different matter. That pattern is associated with better long-term health.

Is it better to get antioxidants from food or supplements?

Based on current evidence, food is the better-supported source. Whole foods provide antioxidants alongside fiber and other nutrients. High-dose supplements have not consistently shown the same benefits in clinical trials (Cochrane).

Do antioxidants slow aging?

Oxidative stress has been linked to aspects of aging and chronic disease (Marrocco et al., 2017). However, there is no strong clinical evidence that antioxidant supplements meaningfully slow aging in humans. The Cochrane review found no evidence to support them for prevention (Cochrane). See antioxidants for healthy aging for more.

How many antioxidants do I need per day?

There is no single official antioxidant requirement. Antioxidants are a broad category of compounds, not one nutrient. Some individual ones do have recommended intakes. Examples are vitamin C, vitamin E, and selenium.

For overall eating, the Dietary Guidelines for Americans recommend about three servings of vegetables and two of fruit daily on a 2,000-calorie pattern.

Can you have too many antioxidants?

Yes, particularly from supplements. Large doses of some antioxidants may interfere with normal cell signaling and defense mechanisms. The risk is much lower with food, since NCCIH notes no safety concerns about antioxidants in food (NCCIH). A few foods can still cause problems. Brazil nuts can deliver excess selenium if eaten in large amounts (NIH ODS).

Related Reading on CollectedMed

• Heart-Healthy Foods
• Anti-Inflammatory Foods
• Mediterranean Diet
• What Is a Balanced Diet?
• What Is a Healthy Diet?
• Healthiest Foods to Eat Every Day
• Omega-3 Fatty Acids
• Cardiovascular Disease
• How to Prevent Diabetes
• Benefits of Exercise

Medical Disclaimer

This article draws on guidance from the National Center for Complementary and Integrative Health (NCCIH), the U.S. Preventive Services Task Force, the NIH Office of Dietary Supplements, the CDC, the American Heart Association, the Cleveland Clinic, the Cochrane Library, and peer-reviewed research. This content is for general education and does not replace personalized medical advice.

Sources

• National Center for Complementary and Integrative Health. Antioxidants: In Depth
• Cleveland Clinic. Oxidative Stress
• Bjelakovic G, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews.
• U.S. Preventive Services Task Force. Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: Preventive Medication (2022)
• NIH Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals
• NIH Office of Dietary Supplements. Vitamin C and Vitamin E fact sheets
• American Heart Association. Mediterranean Diet
• CDC. About Physical Activity
• U.S. Department of Agriculture and HHS. Dietary Guidelines for Americans, 2025-2030
• Marrocco I, Altieri F, Peluso I. Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans. Oxid Med Cell Longev, 2017.
• Oxidative stress: fundamentals and advances in quantification techniques. Frontiers in Chemistry, 2024.
• Oxidative stress: from molecular studies to clinical intervention strategies. Frontiers in Molecular Biosciences, 2025.