Excerpts from “Antioxidants: Natural Defense Against Oxidative Stress,” by Barbra Wexler, MPH
The Perils of Free Radicals
Many of the body’s natural biological processes create harmful byproducts including toxic chemicals called free radicals. These byproducts, collectively referred to as oxidants, can set up chain reactions in the body that damage cells, block the action of critical enzymes and interfere with a wide variety of healthy cellular processes. Oxidants can injure our cell membranes, damage DNA, interfere with the proper division and replication of cells, and block the generation of energy the body needs to run.
In addition to oxidants that arise from natural biological processes, many other factors including stress, illness and poor nutrition can create additional oxidants. Free radicals are also produced in response to environmental exposures such as cigarette smoke, air pollution, insecticides, some fried or burnt foods, alcohol, radiation, chemicals and environmental toxins.
Taken together, these factors can create a condition in the body referred to as “oxidative stress.” While oxidative stress is not itself a disease, high levels of unresolved oxidative stress can weaken the body and contribute to the development of many serious illnesses, especially those of a chronic or degenerative nature.
One serious issue that can occur is advancing age. As a result, the body’s tissues and cells become more susceptible to free radical attacks and damage from oxidative stress. Oxidative stress has been implicated as a factor contributing to the development of more than thirty different disorders—from heart disease and stroke to Alzheimer’s disease and cancer.
The Importance of Antioxidants
Fortunately, the body is poised to effectively respond to the damage caused by free radicals and other oxidizing chemicals. Antioxidants are chemical scavengers that bind to harmful oxidants and neutralize them. In a sense, antioxidants are chemical decoys that allow themselves to become the targets of oxidation, thus sparing our vital tissues and important chemical reactions from damage. Antioxidants help our bodies deal with oxidative stress caused by free radical damage.
We’ve all heard that antioxidants are important to our health. But if we look closely at the word antioxidant it may seem like a paradox. After all, oxygen is essential to our well being. Why should we want to oppose it with an antioxidant? Breathing oxygen connects us to life. If the brain is deprived of oxygen for more than a few minutes, irreparable damage occurs, followed by death. So why should the body need an abundance of antioxidants—chemicals that fight the effects of oxygen?
The answer to this question lies in the subtle but essential distinction between oxygenation and oxidation, a truly profound difference that takes us back to the evolutionary roots of the one hundred trillion cells in our bodies. The two-faced nature of oxygen—on the one hand an essential nutrient that we can’t live without, and on the other a savage destroyer that must be blocked and opposed—is known as the oxygen paradox.
Dietary Sources of Antioxidants
So how do we get antioxidants? Fruits, vegetables and cereals, including barley, corn, millet, and oats, and legumes, including broad beans, pinto beans, and soybeans, are potent sources of antioxidant vitamins. Fruits and vegetables also contain a variety of phytonutrients that often act as antioxidants, protecting the cells of the body from the damaging effects of free radicals. Some of the best sources of antioxidants are berries, ginger, pomegranate, sunflower seeds and walnuts.
Citrus fruits and berries contain bioflavonoids such as hesperidin and anthocyanins, while vegetables such as Brussels sprouts, peppers, kale and spinach contain quercetin, apigenin, myricetin and luteolin. Corn, egg yolks and green vegetables contain lutein and zeaxanthin, and meat, especially organ meat, contains alpha-lipoic acid, coenzyme Q10 and selenium.
But fruits, vegetables, cereals and legumes are not the number-one source of antioxidants in the U.S.diet because most Americans don’t even come close to eating the recommended amounts of fruits and vegetables. (The 2005 Dietary Guidelines for Americans recommend 2 to 6 ½ cups of fruits and vegetables a day, or the equivalent of 4 to 13 servings depending on your age, gender, and activity level.)
Surprisingly, coffee is the leading source of antioxidants in the U.S. diet—not because it is especially high in antioxidants, but because Americans drink so much of it. Their morning coffee gives Americans nearly 1,300 mg daily of antioxidants in the form of polyphenols. The second and third dietary sources of polyphenols in the U.S. diet are black tea (294 mg) and bananas (76 mg) followed by dry beans (72 mg/day), corn (48 mg/day), red wine (44 mg/day), beer (42 mg/day), apples (39 mg/day), tomatoes (32mg/day), and potatoes (28 mg/day).
A List of Well-Known Antioxidants
There are literally thousands of naturally occurring antioxidants, but to get you started, here is a list of better-known antioxidants and the dietary sources of these nutrients.
Alpha-lipoic acid: Red meat, liver and yeast
Beta-carotene: Yellow, orange and green fruits and vegetables such as apricots, carrots, kale, kohlrabi, parsley, spinach and turnip greens
Coenzyme Q10: Organ meat is a potent source of CoQ10, and mackerel, peanuts, sardines, soybeans, spinach, beef and chicken contain smaller amounts.
Ellagic acid: Berries, pecans, pomegranates and walnuts
Epicatechins, catechins and thearubigins: Green tea and black tea
Hesperidin: Citrus fruits are the most potent sources
Lutein and zeaxanthin: Corn, egg yolks, and green vegetables and fruits (broccoli, Brussels sprouts, kale, cabbage, green beans, green peas, spinach, kiwi, and honeydew melon)
Lycopene: Red and pink fruits including papaya, pink grapefruit, pink guava, tomatoes and watermelon
Proanthocyanins: Grape seed extract
Quercetin: Green tea, onions and red wine
Selenium: Seafood, meat, and organ meats. Plant sources such as whole grains and seeds vary in content depending on the selenium content of the soil where they were grown.
Turmeric: The spice is commonly used in curries and South Asian cuisine. Its active ingredient is curcumin.
Vitamin C: Berries, broccoli, Brussels sprouts, cabbage, citrus fruits, collard greens, cauliflower, guava, kale, melons, spinach, sweet peppers, water- cress, turnip greens
Vitamin E: Unprocessed vegetable oils. Smaller amounts are found in whole grains, dark-green leafy veg- etables, legumes and nuts