Often touted as a panacea for practically every disease under the sun, antioxidants have gotten a lot of attention in recent years due to their myriad health benefits. With the capacity to curtail the spread of cancer, dementia, cardiovascular disease, vision loss, and other chronic conditions that crop up as we age, do antioxidants really hold the key to vitality and longevity?
The Free Radical Theory of Aging
First put forth by Denham Harman in 1956, the free radical theory of aging posits that we – and other organisms – age as cells become damaged over time by free radicals.
All the molecules in the human body are composed of atoms that are held together with two electrons. Free radicals are molecules that contain only one electron. They are introduced into the body when you breathe, eat certain foods, and when food is turned into energy.
Because electrons are most stable when in pairs, free radicals will “steal” an electron from another pair, causing the original molecule to become a free radical itself. Setting off a chain reaction, this newly created free radical will steal from another electron pair, which will in turn take an electron from another pair, and on and on it goes.
Ultimately, unpaired electrons cannot function properly. Damage caused by free radicals, a phenomenon called oxidative stress, leads to the death of affected cells in the body. It can dramatically change the cell structure of proteins and lipids while altering the instructions coded in DNA. Oxidative stress has been implicated in a dizzying array of diseases: cancer, cardiovascular disease, ADHD, depression, Parkinson’s disease, chronic fatigue syndrome, Alzheimer’s disease, cataracts, diabetes, celiac disease, bipolar disorder, fibromyalgia, arthritis, influenza, and multiple sclerosis – to name just a few.
To minimize oxidative stress, our bodies do have a built-in defense. Enzymes called superoxide dismutase (SOD) and catalase are synthesized by the body to either remove or add an electron to every free radical molecules it encounters. These enzymes won’t completely mitigate the effects of free radicals, but they do degrade them so they are less damaging to the body.
Free radicals are generated by simply breathing oxygen, exercising, and digesting food. They are also found in fried foods, alcohol, cigarette smoke, air pollution, sunlight, and some medications. Unfortunately the antioxidants our bodies naturally produce are not enough on their own to combat the damage caused by free radicals – and this is why supplementing the system with a diet rich in antioxidants is thought to ease oxidative stress.
How Antioxidants Neutralize Free Radicals
The mechanism of antioxidants is wonderfully simple: When introduced to the body, antioxidants seek out free radicals and generously donate an electron to create a pair. Through this action, the antioxidant molecule sacrifices itself in the process.
There are hundreds – and perhaps even more – substances that act as antioxidants. Although various vitamins, minerals, and plant chemicals have antioxidant properties, they are not one and the same. Each type has its own unique biological and chemical behaviors, evolving in conjunction with each other to fulfill different functions. This means that to get the most benefit, you’ll need to consume many kinds of antioxidants for optimal health.
(Side note: to call a substance an antioxidant is a misnomer; vitamin C, for example, isn’t an antioxidant per se, but it has antioxidant properties because it inhibits oxidation by becoming an electron donor.)
7 Types of Antioxidants & Top Food Sources
So far, there are nearly 500,000 scientific studies on the action of antioxidants, and new types (and subtypes) of free radical scavengers are being discovered all the time. While we couldn’t possibly cover all of them here, these are the antioxidants you don’t want to miss out on:
A class of phytonutrients, carotenoids are plant pigments that give many fruits and vegetables their vibrant red, orange, and yellow hues. Though there are more than 600 types of carotenoids, these are most commonly found in the Western diet:
Beta-carotene – Becoming vitamin A when ingested, beta-carotene helps maintain healthy skin and eyes. Its protective properties work best when consumed along with vitamins E and C. Foods rich with beta-carotene include carrots, mangoes, pumpkin, cantaloupe, papaya, and sweet potatoes.
Alpha-carotene – Though it produces only half of the vitamin A that beta-carotene does, consuming alpha-carotene has been associated with longevity, and people who have high levels of it in their bodies have a lower risk of death from all causes, including cancer and cardiovascular disease. Alpha-carotene is found in many of the same foods as beta-carotene, as well as tangerines, tomatoes, winter squash, and peas.
Lycopene – A potent antioxidant, lycopene may help reduce the risk of prostate cancer, osteoporosis, stroke, and lung cancer. It is found in red fruits such as watermelon, tomato, grapefruit, red cabbage, red bell pepper, and guava.
Lutein – Best known for its role in maintaining vision, lutein was among the most effective carotenoids to reduce the risk of developing age-related macular degeneration, or the loss of central vision. Lutein may also help protect against light-induced skin damage and several diseases such as lung and breast cancer, heart disease and stroke. This carotenoid is found in leafy greens like kale, collard greens, and spinach, as well as broccoli, Brussels sprouts, and green beans.
There are more than 6,000 subgroups belonging to the flavonoid family, making it the largest class of phytonutrients known to date. Along with the capacity to scavenge free radicals, flavonoids have an anti-inflammatory, anti-diabetic, anti-cancer, and neuroprotective effect by virtue of their ability to regulate cell-signalling pathways and gene expression. Here are the most common flavonoids:
Anthocyanins – With at least 600 types unto itself, anthocyanins (and their sugar-free counterpart anthocyandins) are responsible for the bright red, blue, and purple colors in fruits and vegetables. In addition to its potency as an antioxidant, studies on anthocyanins indicate that this nutrient may help protect against several forms of cancer, as well as cardiovascular disease, and obesity. Foods high in anthocyanins include berries, grapes, plums, black currants, cherries, red cabbage, and eggplant.
Flavonols – Four major phytochemicals belong to the flavonol subgroup: quercetin, myricetin, isorhamnetin and kaempferol. Consuming these flavonols has been linked to improved mental and physical performance and a reduced risk of coronary heart disease mortality. Flavonols are found in apples, onions, kale, broccoli, berries, and black and green teas.
Flavanols – Catechins are among the members of the flavanol subgroup, found most abundantly in white, green, and oolong tea, as well as cocoa. Studies on the effects of consuming catechins have found that drinking tea has been linked to reduced body fat in men and eating chocolate has been shown to give the brain a boost.
Isoflavones – Acting as a phytoestrogen – a plant-derived dietary source of estrogen that produces hormonal activity in the body – isoflavones are believed to have a beneficial effect on estrogen receptors in the bone, liver, brain, and heart. Present in soybeans, soy foods, and legumes, isoflavones may help reduce the risk of recurrence for breast cancer survivors, increase bone density, relieve some of the symptoms of menopause, and improve cognitive health in both women and men.
Flavones – Another important flavonoid with robust antioxidant properties, flavones include luteolin, chrysin, apigenin, and baicalein. Flavones have demonstrated anti-tumor, anti-microbial, and anti-inflammatory activities, and are present in foods like parsley, hot peppers, celery, and thyme.
We know that consuming a wide range of vitamins is vital to health, but not all vitamins act as antioxidants.
Vitamin A – Important for immune function, vision, and healthy skin and bones, vitamin A also helps protect against free radicals. As mentioned above, beta-carotene functions as provitamin A and is found in many fruits and vegetables. Retinol is another form of vitamin A, found only in animal-based foods like cod liver oil, butter, cheddar cheese, eggs, and milk.
Vitamin C – Also known as ascorbic acid, vitamin C not only scavenges free radicals, it also helps to restore the antioxidant properties of vitamin E. Unlike other mammals, humans are unable to make vitamin C and must obtain it from our diet. Good sources of vitamin C include citrus fruits, cantaloupes, kiwis, mangoes, berries, bell peppers, broccoli, and spinach.
Vitamin E – Like vitamin A, vitamin E is fat-soluble and is stored by the body and used when needed. Acting as an electron donor, vitamin E also helps to slow the aging process within cells in the body. You can obtain vitamin E from plant seeds (sunflower seeds, almonds, peanuts, and hazelnuts) vegetable oils (olive oil, canola oil, and palm oil), as well as avocado, asparagus, and Swiss chard.
A phytochemical found in cruciferous vegetables like broccoli, cauliflower, cabbage, arugula, radish, wasabi, daikon, and mustards, isothiocyanates are sulfur-rich compounds. Since they are toxic to the plants that generate them, isothiocyanates remain inert until the plant is chewed, cut, or otherwise damaged, acting as a natural defense against pests and disease.
Although isothiocyanates are indeed toxic to humans at exceedingly high doses, they also have demonstrable health benefits and antioxidant properties. Studies on the cancer-fighting activity of isothiocyanates have found that it prevents carcinogens from becoming activated, reduces the damaging of effects of cancer causing chemicals, and hastens the removal of these toxins from the body.
Produced by plants as a response to stress, fungal infection, and injury, resveratrol is found in red wine, cocoa, peanuts, cranberries, blueberries, and the skin of grapes.
Of great interest to the scientific community since the 1990s, resveratrol has been shown to be a potential preventative and treatment for cancer, cardiovascular disease, and neurodegenerative diseases in animal studies. Though it has yet to be rigorously tested in human trials, in vitro studies have revealed that it effectively neutralizes free radicals while boosting our inborn antioxidant defenses like SOD, glutathione, and catalase.
Responsible for giving red wine and unriped fruit its pucker-inducing astringency, tannins (or tannic acid) are a natural preservative, inhibiting the growth of many viruses, bacteria, yeasts, and fungi. They are present throughout the plant kingdom, found in the bark of hardwood trees, as well as berries, nuts, legumes, cocoa, and in drinks like coffee, tea, beer, and wine.
Despite the fact that consuming tannins in high concentrations has been linked to liver damage, cancer, and the malabsorption of vitamins and minerals, eating foods that contain tannins is perfectly safe.
Tannins are potent antioxidants. In addition to scavenging free radicals, tannins have been shown to cleanse the body of heavy metals, protect against tumors and cardiovascular disorders, reduce the risk of death due to burn injuries, speed up the healing of wounds, and treat inflammation.
7. Coenzyme Q10
Another antioxidant we make ourselves, coenzyme Q10 (CoQ10) is crucial for the healthy functioning of our cells. The production of CoQ10 declines as we age and is often deficient in people who suffer from heart conditions, diabetes, cancer, and Parkinson’s disease.
Though it may be taken as a supplement, CoQ10 is readily found meat, poultry, and fish, as well as soybeans, nuts, canola oil.
The Final Word
Theoretically, supplementing your diet with antioxidants should not only slow down the aging process, but also prevent chronic conditions and age-related diseases. But rarely is life so simple.
Since the term “antioxidant” entered mainstream consciousness in the 1990s, it has been flung around with reckless abandon. Adding vitamins, minerals, and phytochemicals to processed food doesn’t automatically make it healthy or give it disease-fighting benefits.
In fact, many studies on antioxidants as disease preventatives have had, at best, mixed results. And in some cases, taking antioxidant supplements led to worsening health, as in the case of smokers who took high doses of beta-carotene supplements which increased lung cancer rates.
That said, the conflicting evidence on the efficacy of antioxidants may lie with the method researchers use to test them. Often, studies on antioxidants are based on synthetic supplements and not natural food sources. Additionally, they may only perform a trial with one antioxidant, such as vitamin E, when antioxidant substances are known to work in conjunction with each other.
Here’s what we do know: a diet of colorful fruits and vegetables keeps the body healthy and is vital for the prevention of many diseases. It might just be we have their antioxidant content to thank for that. Although taking a high-dose antioxidant supplement could be harmful to the body, there’s no evidence that eating food naturally enriched with antioxidants has any potentially damaging effects.