High Doses of Antioxidant Supplements Can Be Harmful

Antioxidant supplements are common and are widely regarded as safe. This is partly because of fruits and vegetables, which are rich in antioxidants and have many health benefits. Still, there is powerful evidence suggests that taking high doses of antioxidant supplements can be harmful. 

Increases Cancer Risk

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The oxidative stress can cause damage to the cells of your body by free radicals. Thus, this is a major contributor to cancer growth.

Because antioxidants neutralize free radicals, it has been hypothesized that taking antioxidant supplements would reduce the risk of cancer development.

Multiple meta-analyses have shown that taking antioxidant supplements does not reduce the risk of many types of cancers once they have been diagnosed. They can even increase the risk of certain cancers.

Several meta-analyses have found that beta-carotene, a precursor of vitamin A, increases the risk of bladder cancer and also the risk of lung cancer in people who smoke.

The only exception is selenium, which may help prevent cancer in individuals with high cancer risk. We need more research before selenium can be recommended for this reason.

The harmful effects of taking antioxidant supplements overshadow its potential benefits. Therefore, taking antioxidant supplements in large doses is harmful, for many reasons.

Decreases Exercise Performance

Naturally, the body produces free radicals during exercise. The harder and longer you work out, the more free radicals the body produces.

Since free radicals may contribute to muscle tiredness and damage, taking antioxidant supplements may blunt their harmful effects, improving performance.

Several studies have shown that taking large doses of antioxidant supplements like vitamins C and E can interfere with how your body adapts to exercise. However, it even loses some exercise-related health benefits.

Get Antioxidants From Food

It is much safer and healthier to get antioxidants from food rather than supplements. All foods contain varying amounts of different antioxidants, so it’s important to include a variety of foods in your diet.

Although animal-based products, such as eggs and dairy products, have antioxidants. However, antioxidants are high in plant-based foods such as fruits and vegetables.

Foods Rich in Antioxidants

Broccoli, bell peppers, spinach, oranges, apples, berries, oats, quinoa, brown rice, kidney, pinto, red beans, walnuts, pecans, almonds, coffee, and tea.

Bottom Line

Antioxidant supplements are safe, but in large doses, they can be problematic. They can diminish the benefits of exercise and increase your risk of certain cancers and birth defects. Having the antioxidants that your body needs via a balanced diet is much better. Before taking any supplements, we strongly recommend consulting with your doctor.

Frequently Asked Questions

What are antioxidant supplements?

Antioxidant supplements contain types of antioxidants free from radical stabilizing substances. As you exercise and digest food, the body creates free radicals. Sources of free radicals are also environmental factors such as UV exposure to air pollutants, tobacco smoke, and industrial chemicals such as pesticides. When free radicals surpass the capacity of your body to control them, then there is a condition called oxidative stress. Over time, this leads to aging and disease growth, including cancer.

Why antioxidant supplements are bad for me?

Taking antioxidant supplements can prevent damage to the cells of the body caused by free radicals. However, taking high doses of antioxidant supplements can also do the opposite.

What are the most common antioxidants?

You can get antioxidants from certain foods and vitamins. Common antioxidants include: Vitamin A, vitamin C, vitamin E, beta-carotene, lycopene, lutein, and selenium.

Can beta-carotene cause birth defects?

Women who may be pregnant should not take high doses of vitamin A. They only recommend such supplements in areas where vitamin A deficiency is prevalent for pregnant women. Beta-carotene, the vitamin A precursor, has not been shown to cause birth defects. However, pregnant women should consult their doctor before taking beta-carotene supplements.


Role of oxidative stress and DNA damage in human carcinogenesis. Mutat Res. 2011.

Procarcinogenic and anticarcinogenic effects of beta-carotene. Nutr Rev. 1999.

Efficacy of Vitamin and Antioxidant Supplements in Prevention of Esophageal Cancer: Meta-analysis of Randomized Controlled Trials. J Cancer Prev. 2013.

Efficacy of antioxidant vitamins and selenium supplement in prostate cancer prevention: a meta-analysis of randomized controlled trials. Nutr Cancer. 2010.

Effects of Vitamin and Antioxidant Supplements in Prevention of Bladder Cancer: a Meta-Analysis of Randomized Controlled Trials. J Korean Med Sci. 2017.

Effects of antioxidant supplements on cancer prevention: meta-analysis of randomized controlled trials. Ann Oncol. 2010.

Free radicals in exhaustive physical exercise: mechanism of production, and protection by antioxidants. IUBMB Life. 2000.

Reactive oxygen/nitrogen species and contractile function in skeletal muscle during fatigue and recovery. J Physiol. 2016.

Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. J Physiol. 2014.

Vitamin C and E supplementation prevents some of the cellular adaptations to endurance-training in humans. Free Radic Biol Med. 2015.

The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutr J. 2010.

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Naeem Durrani BSchttps://defatx.com/
I am a retired pharmacist, nutrition expert, journalist, and more. My interests include medical research, and the scientific evidence around effective wellness practices, which empower people to transform their lives.

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