Can You Have Too Many Antioxidants?

Have a question about science, health, fitness, or diet? Get cited, evidence-based insights with Consensus.

Try for free
Written by Consensus
12 min read

Can you have too many antioxidants?

Check out this answer from Consensus:

While antioxidants are essential for combating oxidative stress and maintaining health, excessive intake, particularly through supplements, can be harmful. A balanced diet remains the safest and most effective way to obtain these vital nutrients. Further research is needed to fully understand the long-term effects of antioxidant supplementation and to establish safe intake levels.

Antioxidants are widely recognized for their ability to neutralize free radicals and reduce oxidative stress, which is implicated in various diseases and aging processes. However, the question arises: can the consumption of antioxidants be excessive and potentially harmful? This article explores the potential adverse effects of excessive antioxidant intake, drawing on recent research findings.

The Role of Antioxidants

Antioxidants play a crucial role in maintaining the balance between oxidation and antioxidation in the body. They help to neutralize reactive oxygen species (ROS) and prevent cellular damage. Common antioxidants include vitamins C and E, selenium, and various polyphenols found in fruits and vegetables.

Potential Benefits

Antioxidants are believed to offer numerous health benefits, including improved sperm quality and fertility in men, as well as protection against chronic diseases such as cancer and cardiovascular diseases . They are also thought to slow down the aging process by mitigating oxidative damage at the cellular level.

The Risks of Excessive Antioxidant Intake

Despite their benefits, excessive intake of antioxidants can be detrimental. High doses of antioxidant supplements have been linked to increased mortality rates and a higher risk of certain cancers . For instance, beta-carotene, vitamin A, and vitamin E supplements have been associated with increased mortality in some studies.

Immunosuppressive and Carcinogenic Effects

There is evidence suggesting that chronic consumption of high doses of antioxidants may suppress the immune system and increase the risk of carcinogenesis. This paradoxical effect is due to the potential of antioxidants to act as pro-oxidants at high concentrations, thereby promoting oxidative stress rather than alleviating it.

Reductive Stress

Excessive antioxidant intake can also lead to reductive stress, a condition where the cellular environment becomes overly reduced, disrupting normal cellular functions. This can be as harmful as oxidative stress and has been linked to diseases such as cancer and cardiomyopathy.

Dietary Sources vs. Supplements

The consensus among researchers is that the optimal source of antioxidants is a balanced diet rich in fruits and vegetables, rather than supplements. Dietary antioxidants work synergistically and are less likely to cause the adverse effects associated with high-dose supplements  .



Can you have too many antioxidants?

Tim Crowe has answered Near Certain

An expert from Thinking Nutrition in Nutrition

Antioxidants have been big news for many years. With promises of preventing and treating many diseases, it is no wonder that they get top billing when assessing the health merits of food. Berries, beans, green leafy vegetables, tea, pecan nuts and dark chocolate are common foods with some of the highest antioxidant values.

 So, what exactly are these antioxidants and what do they do? Antioxidants serve important roles in our body. One of these is helping to mop up excess free radicals. Free radicals are unstable molecules that can damage cells. They form when atoms or molecules gain or lose electrons. The body generates free radicals as the inevitable by-products of turning food into energy. Free radicals are also formed after exercising or exposure to cigarette smoke, air pollution, and sunlight.

 The body can cope with some free radicals, and even needs them to function effectively. However, the damage caused by an overabundance of free radicals over time may become irreversible and lead to certain diseases including heart disease and some cancers. This is because a free radical can damage other molecules as it seeks out electrons to stabile itself.

 Having an imbalance of electrons makes the free radical unstable and places the body in a state of oxidative stress. Oxidation can be accelerated by stress, cigarette smoking, alcohol, too much sunlight, pollution and other factors. Oxidative stress and an excess of free radicals can lead to damage of:

  • Nucleic acids leading to cancerous changes
  • Membrane lipids and LDL-cholesterol in arteries
  • Enzymes which repair cell structures
  • Other proteins such as collagen

We aren’t defenceless against free radicals because antioxidants can short-circuit the damage caused by free radicals and prevent or reduce the damage caused by oxidation. So, it seems logical that the more antioxidants a person eats, the healthier they will be.

 Antioxidants came to the public’s attention in the 1990s when scientists began to understand that free radical damage was involved in the early stages of heart disease, cancer, vision loss, and a host of other chronic conditions. Some studies showed that people with low intakes of antioxidant-rich fruits and vegetables were at greater risk for developing these chronic conditions than were people who ate plenty of those foods.

 Antioxidants though are not just one molecule, they represent a property that is part of many vitamins and minerals such as vitamins A, C and E, and the minerals copper, zinc and selenium. But there are thousands of other chemicals that have some potential antioxidant activity and these compounds are called polyphenols. There are over 8,000 different types of polyphenols found in fruits, vegetables, grains, legumes, tea and coffee.

A brief reading about polyphenols on the Internet will bring up article after article highlighting that polyphenols are antioxidants and that explains their health benefits. Nutrition science though has well-and-truly moved on from using such simplistic language and concepts to describe how these thousands of polyphenols found in food work. They are much more than antioxidants. Focusing only on antioxidants or a single phytonutrient is like zeroing in on a section of a painting and seeing only the dots. You need to step back and see the bigger picture. It should instead be about polyphenols and their multitude of benefits and actions in the body such as:

  • Regulating cell growth and death
  • Slowing down cancer cell proliferation
  • Altering glucose responses and insulin sensitivity
  • Increasing activity of enzymes involved in removing harmful substances from the body
  • Decreasing inflammation

 For many years, food manufacturers promoted the antioxidant capacity of foods assessed by in vitro oxygen radical absorbance capacity (ORAC) testing. A database with ORAC values was maintained in the past by the United States Department of Agriculture. The database highlighted foods with high ORAC scores, including cocoa, berries, spices, and legumes. This ORAC test though only applies to what is happening in a test tube and there is a very big question mark hanging over extending this to what actually happens inside the body. The ORAC database was removed from their website in 2012 because of misuse in the promotion of food and supplements. So, the concept of antioxidant capacity of food is just a very small part in assessing the overall health merits of the food.

And with antioxidants, more is not always better. There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from food and presented in tablet form. In fact, some antioxidant supplements have been found to actually increase cancer risk. For instance, vitamin A as beta-carotene when it is part of food has been associated with a reduced risk of certain cancers. But taken in a supplement form, there is clear evidence that it increases cancer risk in some people, especially lung cancer in smokers.

In fact, a 2010 meta-analysis of randomised controlled trials that used antioxidant supplements to help prevent cancer, found zero evidence for a benefit of supplements containing vitamin A, vitamin C, vitamin E, beta-carotene or selenium.

Because antioxidants are needed for normal physiological functioning, foods containing them are important to include in our diets. But foods high in antioxidants are also high in thousands of other plant chemicals that have a multitude of physiologic effects on the body. Focus instead on eating a diversity of these plant foods and focus less on antioxidants. It is the diversity of foods, especially plant foods that matter most for good health, not their antioxidant content.


Can you have too many antioxidants?

Cornelie Nienaber-Rousseau has answered Near Certain

An expert from North-West University in Nutrition

Our bodies use oxygen in metabolic reactions. Oxygen reacts with body compounds to form molecules known as free radicals. In addition to body processes, free radicals are generated during exposure to ultraviolet radiation, air pollution and tobacco smoke. Free radicals are unstable molecules with one or more unpaired electrons. Because free radicals can oxidize macromolecules (DNA, proteins and lipids) in the body, they have been linked to the onset of cancer, diabetes, and cardiovascular diseases (Aspulund, 2002, Barber et al., 1994). Antioxidants are chemical compounds that protect us against the adverse effects of free radicals by donating an electron or two to neutralize them. Key dietary antioxidant nutrients include vitamin C, vitamin E, beta-carotene (vitamin A) and selenium (Whitney and Rolfes, 2020). Nonnutrient compounds found in plants known as phytochemicals are also antioxidants (Guan et al., 2021). Together the nutrients and nonnutrients with antioxidant activity “limit free-radical formation, stimulate antioxidant enzyme activity, repair oxidative damage, stimulate enzyme activity for repairs and support a healthy immune system” at physiological levels typical of healthy diets (Whitney and Rolfes, 2020). However, at pharmacological doses attained through consuming supplements they may act as prooxidants themselves.

Vitamin C is one of the water-soluble vitamins. Vitamin C is known as the bodyguard for water soluble substances in cells and body fluids protecting tissues when the production of oxidants and free radicals exceeds the body’s ability to defend against them a condition known as oxidative stress (Whitney and Rolfes, 2020). Also vitamin C protects iron from oxidation in the small intestine thereby enhancing iron’s absorption. Because vitamin C is water soluble, it is readily excreted and toxicity symptoms such as gastrointestinal distress and diarrhea are rare. However, excessive supplementation can lead to vitamin C quantities exceeding the body’s need. Vitamin C’s tolerable upper level for consumption is 2000 mg/day. Above this level the beneficial effects on iron absorption can become harmful – too much free iron can cause cellular damage typically inflicted by free radicals (Kazmierczak-Baranska et al., 2020).

Vitamin E is a collective name for several related tocopherols and tocotrienols which are fat soluble and have antioxidant properties. Of these, tocopherol, is the most important antioxidant protecting membranes form oxidation by reacting with lipid radicals (Herrera & Barbas 2001). Vitamin E toxicity is rare but it is recommended that intake do not exceed 1000 mg/day because too much vitamin E could interfere with the blood-clotting action of vitamin K and enhance the effects of drugs used to oppose blood coagulation causing bleeding (Traber, 2008). Summaries of experimental studies i.e. meta-analyses suggested that vitamin E supplementation increased mortality (Miller et al., 2005).

Vitamin A and its pre-cursor beta-carotene have been endowed with antioxidant properties capable of protecting the body against type II diabetes (Marcelino et al., 2020), metabolic syndrome (Beydoun et al., 2019) and protecting the eyes from light damage and age-related macular degeneration (Khoo et al., 2019). Vitamin A toxicity is a real possibility when concentrated amounts of preformed vitamin A in foods or supplements are consumed exceeding 3000 mg/day discoloring the skin. In excess this antioxidant may act as a prooxidant. Whereas fruits and vegs containing beta-carotene prevent cancer, the researchers of the Beta-Carotene and Retinol Efficacy Trial (CARET) observed that smokers given beta-carotene and vitamin A supplements had increased rates of lung cancer (Omenn et al., 1996). Results of the CARET was subsequent confirmed by others (Bejelakovic et al., 2007).

Our bodies must regulate selenium metabolism and transport, because high doses (400ug/day) are toxic. Toxicity symptoms include loss and brittleness of hair and nails; skin rash, fatigue, irritability and nervous system disorders and presenting with a garlic breath odor (Whitney and Rolfes, 2020). Selenium toxicity is characterized with prooxidant activities (Mézes and Balogh, 2009; Zwolak and Zaporowska, 2011).

Plant-derived bioactive antioxidants seem to lower cancer in people whose diets include abundant vegs and fruits (Aspulund, 2002). Summaries of the scientific studies on antioxidant supplements (beta-carotene, vitamin A, vitamin C (ascorbic acid), vitamin E, and selenium) for prevention of cancers found no evidence that they prevent cancers (Bjelakovic et al., 2004). In fact high doses of some antioxidants (beta-carotene, vitamin A, and vitamin E) may have harmful long-term effects, seem to increase overall mortality (Bjelakovic et al., 2004; Bejelakovic et al., 2007). Antioxidants should preferably come from food and not be supplemented and when smoking supplementation should be proscribed. Consuming foods rarely cause toxicities, but supplements can. I recommend a diet rich in fruits, vegetables, and grains and microgreens (immature plants, often used in garnishes) as its content of nutrients with antioxidant properties as well as phytochemicals that may have the potential to prevent or improve chronic diseases.

For more information on antioxidants also refer to my answer on the question Are foods with antioxidants in them really as important as they’re made out to be?


Can you have too many antioxidants?

Margreet Vissers has answered Uncertain

An expert from University of Otago in Vitamin C, Biochemistry, Cancer Immunology

Generally our body makes most of its antioxidant enzymes in the right amounts needed. Some are dietary vitamins and minerals (e.g. Vits C, A and E, selenium) where intake needs to be controlled according to usage. Some of these can be overdosed (Vit A,E and selenium are toxic in high doses). The toxicity limit for Vit C intake is not determined.


Can you have too many antioxidants?

Jens Lykkesfeldt has answered Unlikely

An expert from University of Copenhagen in Pharmacology, Toxicology, Vitamin C

Probably not. However, ingesting enormous amounts of antioxidants does not necessarily improve your health. As many molecular signaling processes and epigenetic control is governed by redox status, it has been speculated that too many antioxidants could in fact be harmful but this has never been documented.

Have a question about science, health, fitness, or diet? Get cited, evidence-based insights with Consensus.

Try for free