We hear the word “antioxidant” more and more these days. I’ve even heard it mentioned in commercials, a sign of how mainstream this term is becoming. Antioxidants are important to our health and may help prevent diseases generally associated with aging. But what, exactly, are they?
What are Antioxidants?
The University of Maryland Medical Center defines an antioxidant as:
A substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism). Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.
What are Free Radicals?
So antioxidants protect the body’s cells from damage caused by free radicals. What, then, are free radicals? Free radicals are unstable molecules that can do damage to all parts of the cell, including cell membranes (walls), proteins, and DNA. As the definition above explains, free radicals are formed during the course of regular metabolism. However, outside influences may lead to free radical formation as well:
Free radicals are formed naturally in the body. In addition, some environmental toxins may contain high levels of free radicals or stimulate the body’s cells to produce more free radicals (source).
Free radical damage to cells occurs as these molecules try to become more stable. For those of you interested in the chemistry behind this process, free radicals are molecules that have either one too many or one too few electrons. Electrons are negatively charged particles that are usually found in pairs. Having an unpaired electron makes the molecule highly unstable. Free radicals look for electrons to “steal” from other molecules in order to become more stable. A molecule that has a “stolen” electron then becomes a free radical itself. This can set off a chain reaction in the body that damages individual cells, and eventually, tissues. Free radical damage to DNA in particular may play a role in the development of cancer (source).
How do Antioxidants Work?
We know that antioxidants protect cells from free radical damage. How do they do this? Antioxidants are able to interact with and neutralize free radicals. I like to think of them as “taking the hit” from free radicals for our bodies.
As was mentioned above, some free radicals are created naturally in the body, as a result of ongoing metabolic processes. External stimuli can promote free radical production as well. This is true, for example, in the case of exposure to radiation from both the sun and from medical x-rays. Environmental pollution can also increase the number free radicals in the body. Not all free radicals are bad, however. The immune system actually creates free radicals that kill viruses and bacteria. In general, though, it is important to keep free radicals in check.
Sources of Antioxidants
The body routinely makes antioxidants to fight off free radicals. The technical term for them is endogenous antioxidants. But our bodies also rely on antioxidants that we take in through diet (exogenous antioxidants). There are numerous molecules that function as antioxidants. Many of them come from plant sources, but a few are found in animal products. Following is a description of some of the more well-known antioxidants and some of their food sources. It is important to note that many antioxidants work synergistically. So eating a variety of foods that contain different antioxidants will help ensure that you get their full benefits. Here are some well-known antioxidants that are found in many common foods.
Flavonoids are a group of compounds that plants produce in order to protect themselves from environmental toxins and to help repair damage. Some of the flavonoids contained in fruits and vegetables have more potent antioxidant activity than vitamins C and E and beta-carotene. These flavonoids actually help protect antioxidant vitamins from damage (an example of how antioxidants work together).
Sources: cranberries, tea, apples, blueberries, red wine, onions, broccoli, tomatoes, nuts and seeds, various spices, and minimally processed dark chocolate (For more on antioxidants in chocolate, click here.)
Carotenoids are another group of phytochemicals (substances produced in fruits and vegetables) found in red, orange, yellow, and green produce. About 50 of these substances can be converted by the body into vitamin A. Carotenoids are actually pigments that help give fruits and vegetables their colors. Some examples of carotenoids are beta-carotene, alpha-carotene, lutein, lycopene, and xeaxanthin. One well-known carotenoid, beta-carotene, is able to halt free radical chain reactions and to protect DNA from free radicals. It also neutralizes unstable molecules created by exposure to sunlight and air pollution.
Sources: brightly colored fruits and vegetables, including carrots, sweet potatoes, spinach, sweet peppers, kale, pumpkins, and watermelon
Green tea is a popular antioxidant drink. It contains compounds called polyphenols that have antioxidant, antibacterial, and antiviral properties. One polyphenol in particular, epigallocatechin gallate (EGCG) is able to penetrate the cell wall and protect DNA from hydrogen peroxide. Black tea may also have similar levels of antioxidants, but in combinations different than what is found in green tea.
Vitamin C is probably one of the best known antioxidants. This vitamin is water-soluble, so it is well-suited to scavenging free radicals in fluids. It also helps prevent damage to artery walls in particular. In addition, vitamin C helps to “recharge” other antioxidants, such as vitamin E.
Sources: citrus fruits, tomatoes, peppers, broccoli, strawberries, papaya, Brussels sprouts
Note: Vitamin C is easily destroyed by heat, so these foods are best eaten raw or lightly cooked if you are trying to increase your vitamin C levels.
Vitamin E helps to protect against free radical damage to fats. Because cell walls are partially constructed of fats, vitamin E helps to prevent damage them. Cell walls act as gatekeepers, determining which substances are allowed to enter and leave the cells. It is therefore important to have healthy cell walls.
Sources: spinach, avocados, sunflower seeds, asparagus, sweet potatoes, nuts
The mineral selenium is not antioxidant by itself. Rather, it is an integral part of glutathione peroxidase, an antioxidant enzyme made in the body. Production of this enzyme therefore depends on adequate levels of selenium.
Sources: garlic, asparagus, grains, brown rice, Brazil nuts, seafood, eggs, tuna, and buckwheat
Garlic contains several molecules and nutrients that function as antioxidants. These include compounds containing sulfur and hydrogen, as well as vitamin C. As noted above, garlic also contains selenium, needed to produce the antioxidant enzyme glutathione peroxidase. Garlic’s sulfur and hydrogen containing compounds bind heavy metals so that they can be excreted from the body. They also help protect against free radicals. In addition, garlic helps prevent fats from being damaged and deposited in tissues and arteries.
For more food sources of antioxidants, see In and Out Sunscreen.
Although free radical damage may be linked to the occurrence of cancer, it is unclear whether or not taking antioxidant supplements reduces the risk of cancer. This may be explained in part by the fact that supplements are composed of isolated nutrients and compounds, while whole foods contain entire complexes of nutrients, enzymes, and other compounds that work synergistically. If you do decide to take an antioxidant supplement, be sure to take one that contains a variety of antioxidants.
Antioxidants are important for protecting cells and tissues from free radical damage. There are many different antioxidants, found in a variety of foods. So eating a balanced diet that includes lots of fruits and vegetables and some nuts, seeds, and grains can help ensure adequate levels.
“Antioxidants and Cancer Prevention.” National Cancer Institute. 16 January 2014. Web. 24 February 2014. http://www.cancer.gov/cancertopics/factsheet/prevention/antioxidants
Balch, Phyllis A. Prescription for Nutritional Healing. New York: Penguin, 2006. Print.
“Dictionary of Cancer Terms.” University of Maryland Medical Center. Web. 23 February 2014. http://www.umgcc.org/patient_info/dictionaryEn/definition/antioxidant.htm
“Heart Health Benefits of Chocolate.” Cleveland Clinic. January 2012. Web. 24 February 2014.
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