What do we really know about antioxidants?

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According to an article in biomoleculesTrusted Source, the word antioxidant is one of the most confusing scientific terms that scientific literature does not clearly defineTrusted Source.
This article takes an in-depth look at antioxidants, explaining what they are and how they affect health.
What are antioxidants?
Antioxidants are compounds that reduce or inhibit cellular damage through their ability to neutralize molecules called free radicals.
Free radicals are molecules that have one or more unpaired electrons in their outer orbit, making them unstable and highly reactive. The body creates them through normal endogenous metabolic processes, including energy production.
The body also produces them in response to environmental and lifestyle factors, such as sun exposure, smoking, alcohol consumption, and more.
Antioxidants inhibit a process called oxidation, which generates free radicals that leads to cellular damage. Antioxidants safely interact with free radicals, neutralizing them before they can cause damage to proteins, lipids, and DNA.
Oxidative stress occurs when there are too many free radicals in the body. This imbalance can occur due to increased production of free radicals or decreased antioxidant defenses.
Free radicals play an important role in the normal physiological functioning of the body and contribute to a person’s health. However, when the body produces an excess of free radicals, it can increase a person’s disease risk.
For example, many chronic diseases, including heart disease and cancer, have links to progressive damage from free radicals.
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Antioxidant defense systems
Cells have antioxidant defense systems that help keep free radical production in check.
For example, cells contain antioxidant enzymes that help reduce free radical levels. The primary antioxidant enzymes in the cells includeTrusted Source superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GRx).
These antioxidant enzymes are known as first-line defense antioxidants. They help regulate free radical levels by neutralizing both free radicals and other molecules that have the potential to become free radicals.
The body also produces metabolic antioxidants through metabolism. These include lipoic acid, glutathione, coenzyme Q10, melatonin, uric acid, L-arginine, metal-chelating proteins, bilirubin, and transferrin.
However, there are some antioxidants that the body cannot produce, which means a person must consume them through food or by taking dietary supplements. These nutrient antioxidants include carotenoids, antioxidant vitamins, including vitamins C and E, selenium, manganese, zinc, flavonoids, and omega-3 and omega-6 fats.
Dietary and supplemental antioxidants tend to receive the most attention within the nutrition world because consuming a diet rich in antioxidants can help boost the body’s antioxidant defenses.
Antioxidants in food vs. supplements
Unraveling the intricacies of dietary antioxidants can be challenging and confusing. Many antioxidants occur naturally in food, and countless other compounds that claim to boost the body’s antioxidant defenses are available as dietary supplements.
Foods such as fruits, vegetables, spices, and nuts contain thousands of different compounds that act as antioxidants.
For example, grapes, apples, pears, cherries, and berries contain a group of plant chemicals called polyphenol antioxidantsTrusted Source. There are over 8,000 different polyphenol antioxidants in nature.
Brightly colored fruits and vegetables also contain high concentrations of carotenoidsTrusted Source, another class of antioxidants.
However, these natural food-derived antioxidants are very different from those found in dietary supplements.
For example, there are many forms of vitamin E, including synthetic vitamin E and natural vitamin E, such as alpha-tocopherol esters. All these forms of vitamin E may have different effects on the body.
This may be why studies investigating the potential health benefits of vitamin E supplements have produced conflicting resultsTrusted Source.
Additionally, supplements typically contain concentrated dosesTrusted Source of isolated antioxidant compounds that can impact health differently than antioxidant-rich foods.
Although antioxidant-rich foods are extremely nutritious and important for health, taking a very high-dose antioxidant supplement may not suit everyone and may even be harmful to some people.
Can antioxidants harm health?
It is clear that a diet concentrated in antioxidant-rich foods, especially fruits and vegetables, is beneficial for overall health.
However, the relationship between supplemental antioxidants and disease prevention is less clear.
Many studies have shown that taking supplements that contain concentrated doses of antioxidants may benefit certain aspects of health.
For example, researchers have linked antioxidant supplements — including omega-3 fatsTrusted Source, curcuminTrusted Source, seleniumTrusted Source, resveratrolTrusted Source, and vitamin CTrusted Source — with various beneficial health outcomes.
However, although certain antioxidants may deliver health benefits when a person takes them for a specific reason, this does not mean that taking supplemental antioxidants is always safe or necessary.
SomeTrusted Source researchTrusted Source suggests that taking certain antioxidant supplements may interfereTrusted Source with the body’s natural signaling pathways and adverselyTrusted Source impact healthTrusted Source.
What’s more, studies have shown that high-dose antioxidant supplements may be harmful in certain populations.
For example, scientists have linked vitamin E supplementation with an increased riskTrusted Source of prostate cancer in healthy men. Similarly, studies have linked beta carotene supplementation with an increased riskTrusted Source of lung cancer in smokers.
Research has also found no clear benefit of antioxidant supplements on disease risk.
Some evidenceTrusted Source suggests that high-dose supplementation with vitamin E, vitamin A, and beta-carotene may increase mortality risk.
This suggests that taking supplements of certain antioxidants may disrupt the body’s natural antioxidant defense network and even harm health when taken inappropriately.
Conversely, research has consistently linked antioxidant-rich diets high in vegetables, fruits, spices, and other natural sources of antioxidants with decreased disease riskTrusted Source and have found no associations with any adverse health outcomes.
For this reason, experts suggest that people should focus on consuming antioxidants through the foods they eat. They do not recommend that people take high-dose antioxidants supplements unless specifically recommended by a healthcare provider.