The research around antioxidant supplements can be confusing

I have to confess to being a bit of a supplement junkie!  I love reading the research around nutrients and one of the reasons I wanted to develop this blog was to become more strategic with my supplement purchases rather than being ad hoc and potentially wasting my money.

These are the most common vitamins and antioxidants that are available as supplements:

Vitamin A (retinol)

Vitamin A (retinol) is natural antioxidant found in both plant and animal products. In plants, it is present in richly colored carotenoids, such as beta-carotene, which can be converted into vitamin A during digestion.

Foods naturally high in Vitamin A are liver, beef, pork, chicken, turkey, fish, eggs and butter, as well a range of dark green and orange-yellow vegetables and fruits including carrots, broccoli leaves, kale, sweet potato, spinach and pumpkin spinach, romaine lettuce, apricots, and capsicum. Increased consumption of fruit and vegetables rich in carotenoids lower oxidative damage. Fresh is best, as vitamin A can be depleted from foods during preparation, cooking, or storage (by radicals produced by prolonged storage or high temperature).

In addition to being an antioxidant, vitamin A maintains the production of cells that divide and regenerate repeatedly, such as those in the skin, as well as the immune system. Vitamin A is also important for vision, particularly at night.

There are two kinds of beta-carotene supplements, those made from natural sources (e.g. palm oil, algae, D. salina) and those manufactured synthetically (all trans beta-carotene). The naturally-sourced carotenes appear to have better antioxidant activity and a lower potential for side effects. When used on its own in clinical trials, vitamin A or beta-carotene did not significantly improve survival of its recipients, and had no significant effects on other age-related complications including, age-related blindness or cancer. In fact, recent studies have suggested that supplements containing beta-carotene (not dietary carotene) may act to promote cancer formation and liver damage in some circumstances, such as in smokers and alcoholics.

Vitamin E (tocopherol)

Vitamin E (tocopherol) is natural antioxidant found in leafy green vegetables, nuts and seeds, whole grains, fortified cereals, and some vegetable oils. However, many of the vegetable oils sold in supermarkets have had the vitamin E removed during processing.

As an antioxidant it is particularly effective in preventing free radical damage to lipids in the cell membranes and circulating fats. In addition, vitamin E also has significant effects on inflammation, immune function and fertility.

Vitamin E is available in both synthetic and natural sources. The natural form is more potent and better absorbed, and should be preferred over synthetic Vitamin E. Natural vitamin E may be sold as alpha, beta, gamma, and delta tocopherol. In general, supplements that contain ‘mixed tocopherols’ with all these different components are emerging as the preferred form of vitamin E supplements. Some manufacturers use this term to mean the synthetic dl-alpha-tocopherol, so we need to read the label closely. When used on its own in clinical trials, alpha tocopherol showed no beneficial effects in terms of heart attacks, strokes, cataracts, cancers or longevity.

Vitamin C (ascorbate)

Vitamin C (ascorbate) is a natural antioxidant found in fruits (such as citrus, currants, strawberries, tomatoes) and vegetables (such as Brassica and peppers). It is also found in high levels in liver, brain and oysters.  It is widely used as a food preservative, especially in processed juices.

Vitamin C is a non-specific antioxidant, with actions on a range of systems. Short term supplementation with vitamin C has been shown to have a number of useful antioxidant effects, including beneficial actions on vascular function, wound healing and immune function. High dose vitamin C can also reduce the severity and duration of symptoms of cold and flu. However, high doses may cause increased bowel activity or diarrhea. This can be lessened by using a buffered form of vitamin C such as calcium ascorbate, or a vitamin C ‘mix’, which combines vitamin C with chlorophyll, hesparin, rutin, and other bioflavonoids. Currently, there are no conclusive clinical trials showing Vitamin C (IN TABLET FORM) has benefits on longevity, cancer risk, heart disease and other age-related complications. However, Intake of foods naturally rich in ascorbate, such as fruits and vegetables, are associated with reduced illness and longevity.


Selenium is a natural constituent of some of the body’s enzymes, including the antioxidant defense enzymes, GPx and thioredoxin. Foods rich in selenium are meat, tuna and eggs. Plants grown in selenium-rich soils also contain increased levels of selenium, including wheat germ, nuts (particularly Brazil nuts), oats, whole-wheat bread, bran, brown rice, turnips, garlic, barley and orange juice. Although most adults have sufficient selenium for their metabolic functions, additional supplementation with selenium increases natural antioxidant activity and boosts immunity and thyroid function. In clinical studies, selenium supplements have been shown to reduce the risk of some cancers and improve the chances for longevity.

Coenzyme Q10

Coenzyme Q10 (also known as CoQ10) is a vitamin-like chemical whose job it is the help the mitochondria use oxygen efficiently. Reduced levels of CoQ10 leads to increased formation of free radicals. CoQ10 is synthesized in the human body with the assistance of numerous vitamins, including vitamin C, vitamins B2, B3, B5, B6, B12, and folic acid. Of these, vitamin B6 has the biggest impact. One way to maintain CoQ10 levels is to have adequate intake of B vitamins. As we get older, our ability to synthesize CoQ10 declines, and we become more reliant on the sources of CoQ10 from our diet.  Foods containing the highest level of CoQ10 are those containing the highest levels of mitochondria, such as liver, kidney and heart tissue, fish and the germs of whole grains.

A number of CoQ10 supplements are now available providing significantly more CoQ10 than that obtained from food. CoQ10 supplements should be taken with meals to help absorption. Clinical trials have shown that these more selective antioxidants can reduce oxidative stress in a range of settings. In studies involving mice CoQ10 can also lead to increased longevity. Whether this will translate into long-term benefits in humans is currently the matter of ongoing trials.

Alpha-lipoic acid

Alpha-lipoic acid is a potent antioxidant, with additional actions to regenerate antioxidant defenses. Foods rich in alpha-lipoic acid are potatoes, carrots, broccoli, beets and yams, as well as red meat.

In the body, alpha-lipoic acid occurs in two forms: R-lipoic acid and R-dihydro-lipoic acid. R-dihydro-lipoic acid exerts a number of antioxidant and neuroprotective actions that are not seen with R-lipoic acid. In particular, R-Dihydro-Lipoic Acid has been shown to improve mitochondrial function, reduce nerve damaging in aging and improve memory and performance. It may also reduce the formation of AGEs. When buying a supplement look for the one that definitely contains the active component. When used as a supplement in high dose generic alpha lipoic acid can produce side effects including skin rash, lowering of blood sugar as well as depletion of B group vitamins, especially B1.


Carnosine is a multifunctional antioxidant made up of beta-alanine and l-histidine. It is found in meat, so is one of the most important antioxidants lacking in a vegetarian diet. Long-lived cells such as nerve cells (neurons) and muscle cells (myocytes) contain high levels of carnosine, where it functions both as a scavenger of free radicals as well as AGEs. Carnosine also acts as an intracellular pH buffer which protects the cell against damage under acidic conditions, such as after exercise. In animal studies carnosine supplements delays the impairment of eyesight with aging. Its long-term effects in human aging are unclear, although it is widely touted as an effective anti-aging therapy.


Lycopenes are red pigments that are important intermediates in the synthesis of many carotenoids. Foods rich in lycopenes are red fruits such as tomatoes, watermelon, pink grapefruit, pink guava, papaya and rosehip. Unlike some of the other vitamins, cooking helps release more lycopenes from the plant fiber, so that tomato paste has more lycopenes than fresh tomato (though less vitamin C as result of processing). In-vitro, lycopenes are more powerful quenchers of free radicals than vitamin E. Diets high in lycopenes are associated with lower rates of prostate and gastrointestinal cancers, as well as reduced risk of heart disease. Lycopene supplementation also boosts immune function and reduces systemic inflammation. The health benefits of lycopene supplements are currently being trialled in a range of clinical settings.


Lutein is an antioxidant in the carotenoid family and is the primary carotenoid present in the central area of the retina, called the macula, where it protects it from oxidative stress. Lutein levels are highest in green leafy vegetable like spinach, kale, collard greens, romaine lettuce, as well as leeks, peas and egg yolks. People who eat more lutein-containing foods appear to be at lower risk of age-related vision loss and cataracts. The benefit of lutein supplements on poor vision in humans is currently being studied. When taking a lutein supplement, take with food containing a healthy fat to improve its absorption.


Polyphenolics represent a range of plant chemicals including the flavonoids, which have potent antioxidant activities. They also have independent actions enhancing cell-protection mechanisms and reducing inflammation. Some of the best-known compounds from this group include the soy isoflavones, quercitin in onions, hesperidin and rutin from citrus, proanthocyanidin in grape seed extract and resveratrol (see below). Each of these compounds, and others like them, has been shown to reduce levels of free radical damage in human studies. Supplements containing complex mixtures of bioflavonoids are now widely available and have been shown to be efficient antioxidant agents.


Resveratrol is the most widely used polyphenolic antioxidant. It is produced in a range of plants (e.g. grapes, peanuts, knotweed) as part of their defense against fungal attack.  Resveratrol is released from grape skin during fermentation, so that red wine, which is fermented before the skin is removed, has higher levels than white wine. However, the amount obtained from red drinking wine is probably insufficient to explain the so called French paradox (the fact that the people of southern France have low rates of heart disease despite their high intake of fats).

Higher and more consistent doses of resveratrol are widely available in health supplements. Most commercially available resveratrol is purified from Japanese knotweed or Hu Zhang root. In this purified form, resveratrol has proven to be a highly effective antioxidant. Apart form scavenging free radicals, resveratrol has been shown to have a number of beneficial effects on human health, including improved efficiency of energy production in mitochondria, activation of beneficial genes associated with longevity, and reduced oxidation of fats.

Epigallocatechin gallate (EGCG)

Green tea is also high in polyphenols with antioxidant properties, including the catechin called epigallocatechin gallate (EGCG). Unlike black tea, which is oxidized before drying, green tea is made from leaves that have undergone minimal processing so the antioxidants levels remain relatively intact. It must be noted that green tea still a lot of contains caffeine (see chapter 15). A number of studies have shown that the intake of green tea (at least 3 cups) is associated with reduced rates of some cancers, heart disease and cognitive decline with advancing age. Because not everyone likes the taste or has time to drink three cups a day, extracts from green tea are available that can be taken in pill form, standardized to contain 80% total polyphenols and 55% epigallocatechin gallate.


Quercetin is an antioxidant found in onions, apples, green tea and black tea. Smaller amounts are found in leafy green vegetables and beans. In addition to scavenging free radicals, quercitin has beneficial effects on mitochondrial function, and thereby preventing radical formation. Quercetin has a range of other actions including effects on clotting, inflammation and blood pressure. It also functions as a phytoestrogen (a plant substance with similar actions to the female sex hormone, oestrogen).

Ellagic acid

Ellagic acid is a polyphenol antioxidant found in many red fruits and berries, including raspberries, strawberries, blackberries, cranberries, grapes, pomegranate and some nuts including pecans and walnuts. Ellagic acid is effective at binding and quenching free radicals and preventing the consequences of oxidative stress in experimental models. In addition, ellagic acid is able to bind and neutralize a number of potent carcinogens and other harmful chemicals. In some trials, pomegranate juice, which is high in ellagic acid as well as other flavanoids has shown some positive benefits on blood pressure and vascular function. Diets high in red fruits have been historically associated with lower rates of cancer and heart disease, although the role of ellagic acid in this benefit remains to be established.
Sulphoraphane is an isothiocyanate antioxidant that is found in broccoli as well as other plants of the cabbage family. The highest levels are seen in broccoli and cauliflower sprouts compared to the adult plants. In experimental studies sulphoraphane has been shown to reduce oxidative stress, as well as prevent some cancers. It also stimulates the functions of the body’s detoxification enzymes and may also be beneficial in the treating the bacteria that causes stomach ulcers.

Indole-3-carbinol (I-3-C)

Indole-3-carbinol (I-3-C) is another antioxidant found in cruciferous vegetables (the cabbage family). I-3-C is released whenever these vegetables are crushed or cooked. I-3-C and diindolemethane, produced when I-3-C is digested, are widely available as supplements. In experimental studies I-3-C has been shown to reduce oxidative stress, as well as slow the growth of some cancers.  Sulphoraphane and I-3-C (along with other glucosinolates and isothiocyanates) associated with the consumption of cruciferous vegetables may contribute lowered risk of prostate, cervical and breast cancer. It should also be noted that I-3-C is also able to modify level of sex hormones including oestrogens, which may contribute to both their anticancer activity and some of their side effects.


Luteolin is a plant flavonoid found in herbs and vegetables including parsley, olive oil, basil, peppermint, capsicum, rosemary and celery. Luteolin is one of the more potent dietary flavonoids in preventing oxidative damage. Luteolin also has a range of effects beyond those of a simple antioxidant, including effects on clotting, inflammation and cancer growth.


Olive juice contains a rich mixture of antioxidant polyphenols, including the major olive oil antioxidant, hydroxytyrosol. Extra Virgin Olive Oil contains more polyphenols than other olive oils, but concentrated olive polyphenols are also available as olive juice extracts. Once discarded as a by-product of the olive oil-extraction process, olive polyphenols have a number of potential health benefits over and above their antioxidant activity.
Another food that is high in polyphenol flavonols is cocoa and dark chocolate (not milk chocolate or white chocolate, or those bars with caramel in the middle). These flavonols have been widely studied in a range of clinical settings. In general, these studies have demonstrated that chocolate flavanols are able to improve blood vessel function, reduce blood pressure and lower cholesterol; features associated with slow aging and improved longevity.


The extract of the Ginkgo leaves also contains a number of polyphenol flavanoids and other chemicals with antioxidant properties. Ginkgo leaf extracts are among the leading prescription medicines in both Germany and France. Apart form its antioxidant effect, Ginkgo has been shown to prevent clotting and improve regional blood flow, particularly in the brain and the heart, as well as the peripheries, where it helps cold hands and feet. Ginkgo also improves blood flow to the penis, which can help boost and maintain erections.  It is widely purported to have beneficial effects on memory and concentration, both in healthy subjects and those with cognitive decline. A number of Ginkgo containing supplements are available. Ideally, look for a ‘standardized extract’ with 24% ‘ginkgo flavonglycosides’ as this is the form that has been tested in studies.

Last Reviewed 01/Mar/2014

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