What is “oxidative stress”? Why does it occur? And what is an antioxidant?

Believe it or not, oxygen – the very thing you need to survive ­— can actually harm you. Think of how the flesh of an apple browns when it’s exposed to air. That’s the effect of oxygen – called oxidation. An antioxidant prevents oxidation. Dipping the cut apple in lemon juice prevents the browning. The lemon juice is an antioxidant. Oxidative stress occurs when someone has too many free radicals in his or her body and not enough antioxidants to combat them.

A free radical is a molecule that contains an oxygen atom that is missing an electron. In its effort to replace the missing electron, the free radical steals from another molecule, which then becomes a free radical itself. It’s a vicious cycle. Antioxidants provide the free radical with its missing electron so that it doesn’t have to steal one from another molecule, thus stopping the cycle.

Your body produces free radicals as byproducts of the many functions it performs, such as when you digest foods, when you exercise, or when you’re exposed to tobacco and other environmental pollutants.

If there are too many free radicals and not enough antioxidants, the balance is off — there are not enough antioxidants to go around, and the damaged cells then become more susceptible to diseases such as cancer, heart disease, etc.

Is there a certain limit to how many free radicals a person should have?

“This is not known. However, some free radicals are needed because they are involved with normal cell signaling,” says Victoria J. Drake, Ph.D., a researcher at the Linus Pauling Institute at Oregon State University. And just as not all free radicals are bad, some antioxidants might not be good: A recent study conducted at Kansas State University found that certain antioxidants can actually suppress key signaling mechanisms necessary for muscles to function effectively. But too many free radicals will cause cellular dysfunction, thereby leading to disease states, Drake adds.

What are some examples of antioxidants?

Antioxidants are found in plants — they protect the plant from ultraviolet light and act as its immune system. Here are a few names you might have read or heard: beta carotene, flavonoids, lycopene, vitamin A, vitamin C, vitamin E and selenium.

Can we get antioxidants from a pill?

We’re still learning what, if any, differences our bodies recognize when we take supplements instead of getting our antioxidants from foods. “Often there’s no distinction between the form of antioxidant in a supplement and the form in a food,” says Karen Collins, M.S., R.D., nutrition adviser to the American Institute for Cancer Research. “But sometimes the chemical form may change slightly. One concern about the use of supplements is the issue of synergy ­ how nutrients and phytochemicals work together differently from the way each one works on its own. (i.e., 1 + 1 = 3 instead of just 2.)”

There is something about the way nature packages fruits and vegetables — the combination of chemicals in plants — that causes them to fight off disease. “High intakes of fruits and vegetables have been associated with a reduced risk for several chronic diseases, including cardiovascular diseases, cancer, type 2 diabetes, osteoporosis and even eye–related disorders such as macular degeneration. Obtaining antioxidants from food is important because foods high in antioxidants also contain other micronutrients and phytochemicals that are important in preventing chronic disease,” says Drake.

In addition, antioxidant supplements are often synthetic (man–made), and some of these synthetic forms may not have the same effects on the body as antioxidants that occur naturally in foods. But even if they are not synthetic, some beneficial properties may be lost when antioxidants are extracted from foods to manufacture supplements.

The other issue concerning supplements is the fact that there’s still scientific ambiguity about what the correct dosage is for optimal effect — and whether or not that dosage changes for specific individuals. Some doctors, for example, have suggested that cancer patients who are following a course of treatment designed to increase the level of free radicals in their bodies may want to avoid antioxidants to help reduce cancer cells. “Correct dosage can be a problem with supplements, because it’s easy to exceed healthy amounts and set the normal balance off,” says Collins. “On the other hand, supplements might turn out to be helpful if it is found that larger amounts of particular phytochemicals do produce benefits. For now, consuming the large amounts possible with some supplements is a risky gamble.”

According to National Institutes of Health’s National Center for Complementary and Alternative Medicine, “Large, long–term studies (randomized, controlled trials) funded primarily by NIH have generally found that antioxidant supplements have no beneficial effects. For example:

  • The Physicians’ Health Study II, which included more than 14,000 healthy male physicians 50 or older, found that neither vitamin E nor vitamin C supplements reduced the risk of major cardiovascular events (e.g., heart attack, stroke or death) or cancer.
  • The Selenium and Vitamin E Cancer Prevention Trial (SELECT) ­ a study of more than 35,000 healthy men 50 or older ­ found that selenium and vitamin E taken alone or together did not prevent prostate cancer. (Two earlier reviews suggested that preliminary evidence for selenium appeared promising.)
  • The Women’s Health Study, which included almost 40,000 healthy women at least 45 years of age, found that, overall, vitamin E did not reduce the risk of death, major cardiovascular events (e.g., heart attack, stroke or death) or cancer. However, it was associated with reduced deaths from cardiovascular causes and also reduced major cardiovascular events in a subgroup of women 65 or older.
  • The Women’s Antioxidant Cardiovascular Study found no beneficial effects of vitamin C, vitamin E or beta carotene on cardiovascular events (e.g., heart attack, stroke or death) in more than 8,000 female health professionals 40 years or older who were at high risk for cardiovascular disease.”

Can taking supplements ever be harmful?

According to Janet Brill, Ph.D., R.D., a Florida-based nutrition expert, there have been thousands of well–designed clinical studies examining the effects of consuming isolated antioxidant supplements such as vitamin E, beta carotene and vitamin C on the development of chronic degenerative diseases. “While most have shown either beneficial or neutral effects, there is some concern over research demonstrating that higher doses can actually increase myocardial events and promote cancer cell proliferation.” For example, the CARET study (The Beta-Carotene and Retinol Efficacy Trial), which looked at more than 18,000 men and women who were smokers, former smokers or workers exposed to asbestos, found that at the end of four years lung cancer incidence was 28 percent higher in those subjects taking beta carotene supplements compared with those taking a placebo.

The Cochrane Library, a well–known scientific research collaboration among world scholars reviewed 67 randomized trials with a combined participation of 232,550 subjects to assess the effects of antioxidant supplements on mortality in primary or secondary prevention. The authors came to the conclusion that there is “no evidence to support antioxidant supplements for primary or secondary prevention.” And, in fact, vitamin A, beta carotene and vitamin E may increase mortality. This review was controversial and disputed by supplement manufacturers and the food industry (specifically those food manufacturers that add supplements to foods).

I’ve seen the term ORAC associated with antioxidants — what does that stand for?

Oxygen radical absorbance capacity. It is one method used to measure the amounts of antioxidants in foods. More specifically, it measures the degree of inhibition of peroxy–radical–induced oxidation of the compound being tested. Another method of testing antioxidant capacity is TAC or Total Antioxidant Capacity. According to Collins, “It’s interesting to note that while there are different methods of measuring antioxidant power, they don’t all come up with foods listed in the same order, which suggests that we still don’t fully understand exactly which best measures the physiological antioxidant effects of foods.” Click here to see the United States Department of Agriculture’s ORAC for selected foods.

Where do you get the most antioxidant bang for your buck?

There’s not a lot of research out there to point us decisively in the direction of a particular food. While we know that many vegetables and fruits are high in antioxidants, we don’t have as much evidence to determine specific amounts in each food. And Collins points out that we need to think about foods a little differently from the way we have in the past — not in terms of rank but in terms of synergistic combinations. “In the old days we seemed to consider certain foods high in particular vitamins ‘better’ than others. Today we know that even when a fruit or vegetable is not a major source of vitamin C or A or antioxidants, for example, it can supply important phytochemicals that improve your overall health.” And while fruits and vegetables are good sources, antioxidants are also found in other foods, including nuts, some seeds, legumes, coffee, tea and chocolate.

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