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What are antioxidants and should you take supplements?

Medically reviewed by Sally Chao, MD. Last updated on Sep 1, 2021.

Official answer

by Drugs.com

Antioxidants are compounds you can consume, such as vitamins and other substances, that can help protect your cells from damage. They do this by blocking the potentially damaging effects of another type of molecule in your body, called free radicals.

Many different chemicals can act as antioxidants. They can be produced naturally by your body or acquired from the foods you eat. Some types of antioxidants are available in dietary supplement form.

Antioxidants fight free radicals

Free radicals are just one of the many threats that your cells must fend off. These molecules are produced naturally by your body and are not harmful at low levels. However, certain environmental exposures can increase their abundance. Smoking cigarettes, breathing in polluted air and getting sunburnt are examples of factors that can increase your levels of free radicals.

Free radicals have the ability to interact with your cells, potentially changing their structure, function and genetic makeup (DNA). This can lead to all sorts of problems when cells start to behave abnormally. However, antioxidants can step in and block this process, protecting your cells from free radical damage.

When your body is exposed to high levels of free radicals over a long period, it can lead to oxidative stress, a condition that comes with excessive cell damage and that may play a role in causing various health issues, including cancer, heart disease, diabetes and Alzheimer’s disease.

Antioxidants can help counteract oxidative stress.

Foods are a rich source of antioxidants

While the benefit of taking in antioxidants through healthy foods such as fruits and vegetables is undisputed, research has not shown that using dietary supplements to boost antioxidants in the body has a clear health benefit. In some cases, high-dose antioxidant supplements may even be harmful.

In general, you can find a rich combination of antioxidants by eating a diet full of fruits and vegetables. People who do so generally face a lower risk of developing chronic diseases. However, antioxidants alone are likely not responsible for these outcomes. The antioxidants in these foods are just one of the many benefits of consuming plenty of fruits and vegetables.

Below are some of the many types of antioxidants, along with examples of food sources they are found in.

Beta-carotene

Contained in colorful fruits and vegetables, including peaches, apricots, mangoes, cantaloupes, papayas, peas, carrots, squash, sweet potatoes, broccoli, kale and spinach.

Lutein

Contained in green vegetables, including collard greens, spinach, kale, broccoli and peas, as well as corn, oranges and papayas.

Lycopene

Contained in fruits and vegetables with red or pink coloring, including watermelon, tomatoes, apricots and grapefruits.

Selenium

Contained in wheat, rice, corn, beef, turkey, chicken, fish, legumes, nuts, cheese and eggs.

Vitamin A

Contained in dairy products and liver.

Vitamin C

Contained in many fruits, including berries, kiwis, oranges, papayas and cantaloupes, as well as many vegetables, including bell peppers, tomatoes, broccoli, cauliflower, kale and Brussels sprouts.

Vitamin E

Contained in almonds, hazelnuts, peanuts, sunflower seeds, spinach, kale and some types of oils, such as soybean, corn, canola and sunflower oil.

Phenolic compounds

  • Quercetin (contained in red wine, apples and onions)
  • Catechins (contained in cocoa, tea and berries)
  • Resveratrol (contained in grapes, red and white wine, berries and peanuts)
  • Coumaric acid (contained in berries and spices)
  • Anthocyanins (contained in strawberries and blueberries)

While scientific evidence supports the notion that eating an antioxidant-rich diet helps prevent various diseases, studies have not come to the same conclusion for antioxidant supplements.

Should you take antioxidant supplements?

Many studies have explored potential relationships between different types of antioxidant supplements and how they may affect your health, sometimes resulting in exciting outcomes. However, the observational studies that uncovered some potential benefits of antioxidant supplementation cannot show that the supplements directly caused the beneficial outcome.

Due to the promising research on this topic, several long-term, randomized controlled clinical trials of antioxidant supplements have now been conducted. These studies can more directly investigate the relationship between health and antioxidant supplements by giving antioxidant supplements to some participants and giving a placebo to others so that the true health outcomes over an extended period can be more fully analyzed.

The results from these high-quality studies have revealed that antioxidant supplements do not seem to have a beneficial effect on disease prevention.

Below are some examples of these studies and their findings:

  • Across nine different randomized control trials testing various antioxidant supplements, results did not suggest that these supplements helped prevent cancer.
  • In a trial testing vitamin E supplements among 40,000 middle-aged women, the results showed that supplementation did not decrease the risk of adverse health outcomes, including cancer, heart attack and stroke.
  • In a trial of more than 8,000 middle-aged women with a high risk of developing heart disease, vitamin C, vitamin E or beta-carotene supplements did not lower the risk of diabetes, cancer or cardiovascular events (heart attack, stroke).
  • In a trial of more than 14,000 middle-aged men, vitamin E or C supplements did not reduce the risk of heart attack, heart disease death, stroke, cataracts or cancer.
  • In a trial of more than 35,000 middle-aged men, vitamin E and selenium supplements did not reduce the risk of prostate cancer.

Beyond the lack of evidence found in these and other trials, some trials found that antioxidant supplements may sometimes cause harm. For example:

  • In the trial testing vitamin C and E supplements on middle-aged men, those who took vitamin E supplements were found to have an increased risk of stroke.
  • In the trial testing selenium and vitamin E supplements on middle-aged men, those who took vitamin E supplements alone were found to face a greater risk of prostate cancer than those who took a placebo.

On the other hand, one example of a trial that did find a potential benefit of antioxidants is the Age-Related Eye Disease Study. In this study, a dietary supplement that combined zinc and the antioxidants vitamin C, vitamin E and beta-carotene lowered the risk of disease progression for certain groups of people with age-related macular degeneration.

Overall, the evidence suggests that you are much better off getting antioxidants from a healthy diet, which comes with many other health benefits besides just the antioxidants. If you are taking supplements or considering doing so, it is important to discuss this with your doctor. Research is still ongoing into the complex interplay between antioxidants, free radicals and your health.

References
  1. National Center for Complementary and Integrative Health (NCCIH). Antioxidants: In Depth. November 2013. Available at: https://www.nccih.nih.gov/health/antioxidants-in-depth. [Accessed August 10, 2021].
  2. National Cancer Institute (NCI). Antioxidants and Cancer Prevention. February 2017. Available at: https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/antioxidants-fact-sheet. [Accessed August 10, 2021].
  3. U.S. National Library of Medicine MedlinePlus. Antioxidants. August 4, 2021. Available at: https://medlineplus.gov/antioxidants.html. [Accessed August 10, 2021].
  4. American Academy of Family Physicians (AAFP). Antioxidants: What You Need to Know. August 5, 2020. Available at: https://familydoctor.org/antioxidants-what-you-need-to-know/. [Accessed August 10, 2021].
  5. Harvard T.H. Chan School of Public Health. Antioxidants. Available at: https://www.hsph.harvard.edu/nutritionsource/antioxidants/. [Accessed August 10, 2021].

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