There are many factors that can contribute to aging and disease, one of which is cellular damage induced by reactive oxygen species, a type of free radical. Free radicals are molecules that are missing at least one electron, which causes them to be unstable and very reactive. (30) The high reactivity of these radicals leads them to oxidize with other molecules in order to gain the electron(s) they need to stabilize. (30) Oxidation reactions can occur with a variety of compounds, such as proteins, lipids, and DNA, resulting in damage to body cells. (30)

One way to minimize or prevent free radical damage and its associated health concerns is by ensuring an optimal intake of antioxidants.

What are antioxidants?

Antioxidants are compounds that counteract free radicals, preventing oxidative stress and cellular damage. (29) They can be produced by our body, consumed through our diet, or obtained through supplements. (29) When the ratio of antioxidants to free radicals is unfavorable, it leads to oxidative stress. (18) Antioxidants can neutralize free radicals by:

  • Inhibiting free radical producing enzymes or receptors
  • Donating an electron to an unstable radical without becoming unstable itself (referred to as scavenging) (17)(18)

Download a handout on antioxidants.

What are free radicals?

Reactive oxygen species are a byproduct of many metabolic reactions. (11) In moderation, these free radical compounds react with antioxidants to regulate many cellular processes, like cell propagation or cell growth. (11) However, when we have an excessive amount of free radicals, cellular damage may occur. Certain lifestyle and environmental factors can increase the production of free radicals, including:

  • Alcohol intake
  • Charred food intake
  • Chronic stress
  • Pollutant exposure (e.g., certain pesticides, mold, smog) (21)
  • Radiation exposure (e.g., ultraviolet rays, x-rays)
  • Smoke inhalation (e.g, cigarette smoke, automobile exhaust) (18)(32)

Maintaining an antioxidant balance may reduce the damage caused by free radicals. (23)

Did you know? In 1956, Denham Harman proposed the “free radical theory of aging”, hypothesizing that free radicals play a crucial role in the aging process. (30)

What is oxidative stress?

Oxidation is a chemical reaction in which electrons are transferred between molecules. (16) Oxidation reactions are important for many biological and physiological processes, such as respiration or photosynthesis; however, when there are more free radicals present than antioxidants, harmful oxidative stress may occur. (16)(23) When we lack antioxidants, free radicals react with our body cells, producing further free radical molecules. (30)

Oxidative stress and aging

As we age, our organs and tissues naturally lose function and work less efficiently. (17) This loss in efficiency makes us more susceptible to cellular dysfunction caused by reactive oxygen species. (6) Cellular damage caused by free radicals has been associated with many age-related chronic conditions, including:

  • Certain cancers (e.g., lung cancer, stomach cancer) (36)
  • Cardiovascular diseases (e.g., atherosclerosis, hypertension, stroke)
  • Diabetes (type 1 and 2) (30)
  • Eye diseases (e.g., age-related macular degeneration, cataract)
  • Inflammatory diseases (e.g., arthritis, lupus)
  • Neurological disorders (e.g., Alzheimer disease, Parkinson’s disease) (18)(23)

Increasing antioxidant intake: diet vs. supplementation

It’s recommended that you try to consume antioxidants through a balanced diet that incorporates a variety of fruits and vegetables, as research suggests that a diet rich in plant foods lowers your risk of many chronic conditions. (23) Numerous foods have been studied for their antioxidant content; however, due to the complexity of whole foods, it’s uncertain whether it’s the antioxidant content or other factors that influence health. (23)

Antioxidant supplements may also help address oxidative stress, but the evidence supporting these remains inconsistent. Further research is needed to fully understand the function, safety, and appropriate dosage of antioxidant supplements. (33)

Antioxidant-rich foods

Individuals experiencing oxidative stress may particularly benefit from an antioxidant-rich diet. You can find antioxidants in a variety of animal and plant-based sources. Nearly all fruits and vegetables provide a source of antioxidants due to their phytonutrient content. (29) Some vitamins and minerals also offer antioxidant properties. (29) The table below provides an overview of some of the most common antioxidants.



Chart showing the common types of antioxidants
These five antioxidant examples are readily available in a balanced diet. There is no Recommended Dietary Allowance (RDA) for phytonutrients, but it is recommended adults consume at least five servings of fruit and vegetables per day. (12)


Did you know? Smoking increases oxidative stress and reduces plasma vitamin C levels. As a result, individuals who smoke require an additional 35 mg per day of vitamin C compared to non-smokers. (24)

Certain foods have been studied for their high antioxidant content. Try adding some of the following antioxidant-rich foods to your diet to combat oxidative stress.

Citrus fruits

Citrus fruits, such as grapefruits, lemons, limes, and oranges, are great sources of antioxidants. These fruits contain a high concentration of vitamins C and E, which have been found, according to in vitro studies, to target lipid peroxidation, a chemical reaction that creates free radical lipids that may contribute to the development of atherosclerosis. (14)(38) Atherosclerosis is the main cause of cardiovascular diseases, including heart attack, heart failure, and stroke. (7)

The high vitamin C content of citrus fruits may make them particularly beneficial against cardiovascular disease, and adequate plasma vitamin C has been shown to decrease the relative risk for a heart attack in adult men. (26)



Citrus fruit
Citrus fruits have been found to contain over 170 antioxidants. (38)


Cocoa beans

The phytonutrient compounds found in cocoa beans include flavanols and catechins. (22) These compounds have been studied for their neurological impact, with findings indicating antioxidant benefits for conditions like Parkinson’s disease and Alzheimer’s disease. (22) Cocoa flavanols have been found to reinforce learning and memory by promoting neurosurvival (neuron resistance to cell death) and neurogenesis (new neuron formation) in our hippocampus. (22)

In addition to neurological protection, cocoa antioxidants also promote cerebral blood flow. (22) This increased blood flow provides oxygen and glucose to our neurons to promote optimal memory processing. (22)

Cocoa is often consumed in chocolate, which typically contains additional ingredients. Other cocoa products include cacao nibs, cacao powder, and unsweetened cocoa powder, which are minimally-processed cocoa bean products that generally don’t contain added ingredients. Unsweetened cocoa products can be used in baked goods, smoothies, or sprinkled over fresh fruit.

Goji berries

Goji berries, also known as wolfberries, are berries from the Lycium plant species native to Asia. They have been used for centuries in Chinese medicine and cuisine. (20) Oxidative damage to our lipid-rich retina is thought to be the leading cause of age-related macular degeneration. Goji berries sourced from the Lycium barbarum plant contain specific polysaccharides (complex sugars) that may offer neuroprotective effects for retina cells. (20)

In addition to these unique polysaccharides, goji berries also contain zeaxanthin, a carotenoid with antioxidant and blue light absorbing properties. (4) Zeaxanthin accumulates in our macula, and has been shown to protect against macular degeneration. (20) Regular goji berry consumption has been found to increase plasma concentrations of zeaxanthin, making this fruit a great addition for those with eye disease. (4)



Bowl of blueberries
Deeply-colored dark berries, such as açai berries or blueberries, have a greater antioxidant content than many other fruits and vegetables. (20)


Green tea

Green tea is one of the most popular beverages in the world. (15) Similar to cocoa beans, green tea is rich in flavanols and catechins. (15) While all varieties of tea possess some antioxidant content, green tea contains a greater concentration of antioxidants because the leaves are not fermented during the drying process. (15)

Regular green tea consumption has been linked to the prevention of certain cancers, including lung cancer and gastrointestinal cancers. (3) Experimental research has found that green tea catechins demonstrate anti-cancer properties by inhibiting tumor formation and promoting cancer cell death. (3)(15)

Red beetroot

Beets, full of phytonutrients that contribute to their deep red color, are an excellent source of antioxidant-rich compounds including vitamin C, carotenoids, and flavonoids. (5) Beets also contain betalains, plant pigments that have been found to exhibit antioxidant properties according to in vitro and in vivo studies. (5) An animal model found that feeding rats beetroot juice daily for a 28-day period reduced lipid and protein oxidation rates and decreased inflammation. (5)

Antioxidant supplements

Using antioxidant supplements may have beneficial effects on a number of age-related conditions. (23) If you’re considering an antioxidant supplement, be sure to check with your integrative practitioner first, as certain antioxidants have the potential to interact with medications and can be toxic. (23)

Some commonly available antioxidant supplements include vitamin C, vitamin E, coenzyme Q10 (CoQ10) and resveratrol. In vitro studies demonstrate that antioxidant supplements are capable of stabilizing free radicals, preventing oxidative cell damage. (23) However, there is limited evidence to support the benefits of antioxidant supplements in vivo and in clinical trials. (23)

Eye health

A clinical study piloted by the National Eye Institute found that supplementation with a combination of zinc and the antioxidants vitamin C, vitamin E, and beta carotene was effective in combating age-related eye disease. (23) This combination of supplements limited the severity of macular degeneration in 25% of participants that had intermediate-stage eye disease. (23)

Cardiovascular health

The same combination of zinc and antioxidant supplements were used at high doses for an eight-week period to study their effect on hypertension in adults. (8) At the end of the period, both hypertensive and normotensive participants experienced reductions in systolic blood pressure. (8)

Type 2 diabetes

Type 2 diabetes has been reported as a risk factor for cardiovascular disease and Alzheimer’s disease. (31) Chronic oxidative stress can promote insulin resistance and impaired insulin secretion in individuals with prediabetes and type 2 diabetes. (19) Insulin resistance impacts certain cells and can lead to further health complications including hypertension (high blood pressure) and neurological dysfunction. (19)(27)

The antioxidant CoQ10 is naturally occurring within our body and is used to promote cell growth. (2) CoQ10 levels decline as we age and tend to be even lower in individuals with heart disease or those who take cholesterol-lowering drugs (e.g., statins). (2) Reports and experimental research indicate that CoQ10 supplementation may lower blood pressure, reduce cholesterol levels, and limit neurological damage related to diabetes. (1)(27)

Digestive health

Resveratrol has been studied for its antioxidant effects related to intestinal inflammation. In an in vivo trial with piglets, it was found that supplementation with resveratrol and curcumin inhibited the release of two critical inflammatory molecules in the intestine. (9) The results of the study may also be attributed to the combination’s impact on intestinal bacteria, as imbalances in gut microbiota may contribute to inflammation and oxidative stress. (9) In the piglets, this combination of supplements protected against certain negative bacteria, including Escherichia coli., but acted as a multiplier for beneficial strains of bacteria. (9)

The bottom line

Antioxidants are complex compounds and further research is necessary to fully understand their functions and benefits. Current research indicates that antioxidants may provide anti-inflammatory, cardioprotective, and neuroprotective effects. Try to consume a diet rich in various fruits and vegetables to ensure you’re optimizing your antioxidant intake. If you’re looking to add an antioxidant supplement to your regimen, be sure to check with your integrative practitioner to find the right fit for you.

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