Antioxidants: The Unbiased Scientific Truth, Evidence-Based Health Benefits, and Important Facts

What is an Antioxidant and why is it Important?

Antioxidants are an essential part of optimal health, and the spotlight is growing on these important nutrients. The use of the word ‘antioxidants’ is becoming quite common in labeling certain foods or products to promote their health benefits.

However, few people really know what they are or how they work in the body.

This article dives into what antioxidants are, their function, their potential health benefits, sources of antioxidants, and any risks involved with antioxidant supplements.

Free Radicals and the Role of Antioxidants

Free radicals

In order to understand the role of antioxidants in the body, it is first important to comprehend the role of free radicals and oxidative stress. Free radicals are highly unstable molecules (or atoms) with an odd number of electrons – they have an unpaired electron in an outer ring.

Electrons normally exist in pairs and when that free radical encounters another molecule, it may steal an electron from it to pair with its own odd electron.

The second molecule, having lost an electron, itself becomes a free radical. This creates a chain reaction of free radical production, also known as oxidation.

Free radicals and oxidative stress are thought to play a role in accelerated aging and a variety of diseases, including cancer, cardiovascular diseases, diabetes, Alzheimer’s disease, Parkinson’s disease, and eye diseases such as cataracts and age-related macular degeneration^[4][5].

Free radicals are found in virtually all dangerous chemicals, including air pollutants, cigarette smoke, and other toxins, and are generated when your body is exposed to radiation, including the sunlight.

They are also created when your body burns food for energy, breaks down harmful chemicals in the liver, or fights infections.

Your body’s white blood cells generate large quantities of free radicals to destroy bacteria and virus-infected cells^[4][5]. Free radicals function as communication molecules that promote or sustain inflammatory reactions, and in chronic inflammation, normal healthy cells can become damaged^[5].

Other lifestyle, stress, and environmental factors are known to promote the excessive free radical formation and oxidative stress include:

• Alcohol intake^[6]
• High blood sugar levels^[7][8]
• Too much or too little oxygen in the body^[6]
• High intake of polyunsaturated fatty acids^[9]
• Excessive intake of iron, magnesium, copper, or zinc^[9]
• Intense and prolonged exercise, causing tissue damage^[4]
• Excessive intake of antioxidants, such as vitamins C and E^[9]
• Antioxidant deficiency^[10][11]

Antioxidants

The definition of antioxidants is “any substance that inhibits oxidation, especially one used to counteract the deterioration of stored food products or remove potentially damaging oxidizing agents in a living organism”^[10].

Antioxidants can also repair and/or clear damaged cells, and some antioxidants can induce biosynthesis of other antioxidants or defense enzymes as well^[11].

Antioxidants are essential for the survival of all living things, including plants and animals. The body produces many different antioxidants (also known as endogenous antioxidants) to protect itself from different diseases due to tissue injury.

The body is unable to produce some necessary antioxidants and therefore external sources, such as food or supplements, are essential in supplying those antioxidants. These externally sourced antioxidants are also referred to as exogenous antioxidants.

Antioxidants can be broken down further into two classes, enzymatic antioxidants, and non-enzymatic antioxidants. Enzymatic antioxidants are networks of antioxidant enzymes that interact and protect cells from oxidative stress^[11][12].

Antioxidants that are produced in the body include, but are not limited to^[11][12]:

• Superoxide dismutase (SOD) (enzymatic)
• Catalase (enzymatic)
• Glutathione and the whole glutathione system (enzymatic)
• Alpha-lipoic acid
• Ubiquinol (Coenzyme Q10)
• Melatonin
• Uric acid
• Metal-binding proteins (examples – transferrin and albumin)
• Bilirubin

Examples of antioxidants that are essential from food include, but are not limited to^{[4][11]–[13]}:

• Vitamin E (tocopherols and tocotrienols)
• Vitamin C (ascorbic acid)
• Carotenoids (especially beta-carotene, zeaxanthin, lycopene, and lutein)
• L-arginine
• Resveratrol
• Manganese
• Selenium
• Flavonoids (including rutin and quercetin)
• Anthocyanins (a type of flavonoid polyphenol phytonutrient)
• Glutathione
• Omega-3 fatty acids

The Health Benefits of Antioxidants

Recent research has shown that the antioxidants of plant origin with free-radical scavenging properties could have great importance as therapeutic agents in several diseases caused by oxidative stress^[11][14].

Research suggests that when it comes to longevity and overall health, some of the benefits of consuming antioxidant foods, herbs, teas, and supplements include^[4][10][11]:

• Slower signs of aging, including the skin, eyes, tissue, joints, heart, and brain
• Healthier, more youthful, glowing skin
• Reduced cancer risk
• Detoxification support
• Longer life span
• Protection against heart disease and stroke
• Less risk for cognitive problems, such as dementia
• Reduced risks for vision loss or disorders, like macular degeneration and cataracts
• Reduced risk for other chronic diseases

Antioxidants are also frequently used as food additives as they can increase the shelf life of both natural and processed foods, due to their role of reducing oxidation.

Antioxidants from Nutrition Sources

Research has demonstrated that nutrition plays a crucial role in the prevention of chronic diseases, as most of them can be related to diet.

Functional food enters the concept of considering food not only necessary for living but also as a source of mental and physical well-being, contributing to the prevention and reduction of risk factors for several diseases or enhancing certain physiological functions. Antioxidants fall under the category of functional foods, as well as essential nutrients^[12].

Regular consumption of fruits and vegetables vitamins has been recognized as reducing the risk of chronic diseases and studies demonstrate that an antioxidant-rich diet has a very positive health impact in the long run^[15]–[17].

Plant-based foods are the best sources of antioxidants. These include fruits, vegetables, whole grains, nuts, seeds, herbs and spices, and even cocoa. Wild-caught fatty fish and grass-fed/wild meat, and eggs are also sources of antioxidants^[1][18].

No one food group should be your sole focus. Instead, be sure to incorporate a variety of fruits, vegetables, nuts, whole grains, herbs and spices into your diet. Aiming to eat the colors of the rainbow can help you obtain a variety of antioxidant nutrients and compounds.

Listed below are some of the richest sources of antioxidants^{[1][5][10][12][18][19]}:

• Fruits (especially berries): blueberries, blackberries, strawberries, raspberries, bilberries, elderberries, cherries, citrus fruits, autumn olives, cranberries, dark purple grapes, prunes, pomegranate, jujube dates, goji.
• Vegetables: sweet potatoes, squash, carrots, red and green peppers, kale, lettuce, spinach, cucumber, green beans, mustard greens, broccoli, cauliflower, cabbage, Brussels sprouts, artichokes (boiled), mushrooms, eggplant, tomato, chili pepper, and kidney beans.
  • Try to choose red, orange, deep yellow and dark green leafy vegetables every day!
• Alliums and other bulbs: garlic, onions, shallots, fennel bulbs, leeks, and scallions.
• Nuts and seeds: flax seeds, hemp seeds, chia seeds, sunflower seeds, pumpkin seeds, walnuts, pecans, and hazelnuts.
• Whole-grains: wheat germ, maize, whole wheat, barley, rye, quinoa, etc.
• Wild-caught fatty fish: salmon, sardines, halibut, herring, mackerel, pollock, trout, tuna, and anchovies.
• Other sources of healthy fats: extra-virgin olive oil, macadamia oil, avocado oil, coconut oil, and olives.
• Beverages: pomegranate juice, red wine, coffee, green tea, black tea, and white tea.
• Herbs: sage, thyme, marjoram, tarragon, peppermint, rosemary, savory, basil, lemon balm, parsley, and dill weed.
• Spices: clove, cinnamon, oregano, turmeric, cumin, parsley, basil, curry powder, mustard seed, ginger, pepper, chili powder, paprika, garlic, coriander, onion, cardamom, nutmeg, caraway, and cayenne.
• Dark chocolate/cocoa: at least 70% dark chocolate.

Antioxidants from Supplements

Most clinical studies of antioxidant supplements have not found them to provide substantial health benefits. Researchers have suggested several reasons for this, including the following^[4]:

• The beneficial health effects of a diet high in vegetables and fruits or other antioxidant-rich foods may be caused by other substances present in the same foods, other dietary factors, or other lifestyle choices rather than antioxidants.
• Differences in the chemical composition of antioxidants in foods versus those in supplements may influence their effects.
• For some diseases, specific antioxidants might be more effective than the ones that have been tested. For example, to prevent eye diseases, antioxidants that are present in the eye, such as lutein, might be more beneficial than those not found in the eye, such as beta-carotene.

It is important to note that there have been some studies showing benefits to antioxidant supplements, including the Age-Related Eye Disease Study (AREDS), which showed that a combination of antioxidants (vitamin C, vitamin E, and beta-carotene) and Zinc reduced the risk of developing the advanced stage of age-related macular degeneration by 25% in people who had the intermediate stage of this disease or who had the advanced stage in only one eye.

Some research has shown that antioxidants like lutein and glutathione may be beneficial when taken in supplement form – for example, in preventing vision loss, joint problems or diabetes.

Quercetin may also be safe and beneficial for helping manage several inflammatory health problems^[10].

Risks to Antioxidant Supplements

Excessive intake of isolated antioxidants can have toxic effects and may even promote oxidative damage, rather than prevent it. This phenomenon is known as the “antioxidant paradox”^[20].

For example, the results of some studies have linked the use of high-dose beta-carotene supplements to an increased risk of lung cancer in smokers. The use of high-dose vitamin E supplements has also been linked to an increased risk of hemorrhagic stroke and prostate cancer^[4].

It is also important to use caution if you are pregnant or nursing or considering giving a child a dietary supplement. Make sure to check with your health care provider beforehand.

Like other dietary supplements, antioxidant supplements may interact with certain medications, for example^[4]:

• Vitamin E supplements may increase the risk of bleeding in people who are taking anticoagulant drugs (“blood thinners”).
• Taking antioxidants may or may not be harmful during cancer treatment.

If you are at risk of heart disease or other chronic diseases or have age-related macular degeneration, consult your health care providers to determine whether a supplement can benefit you.

Conclusion

Antioxidants are an essential part of optimal health. The body produces certain antioxidants, while other antioxidants need to be supplied from sources outside the body.

It’s always ideal, and usually more beneficial, to get antioxidants or other nutrients directly from real food sources, specifically plant-based food sources.

However, certain types may be helpful when consumed in supplement form, but it is important to check with your doctor beforehand.

Meghan Rittmaster, MS, RDN, LD

Meghan is a registered dietitian nutritionist in private practice in Minneapolis. Her areas of expertise include functional nutrition a... [Read Full Bio]