July 15, 2010

Science, Supplements and Superfruits

How much do we really know about antioxidants? Tufts researchers sort the conflicting claims

By Jacqueline Mitchell

Walk down any aisle in the grocery store and you’re likely to see the word “antioxidant” emblazoned on the labels of multivitamins, juices, teas, energy bars, even cereal boxes. It’s a nutritional buzz word that suggests a product is good for what ails you.

“The moral of the story is eat the berries,” says James A. Joseph. Illustration: Federico Jordan

Manufacturers claim that antioxidants, naturally occurring chemical compounds found in most plants, reduce the damage of aging and can prevent certain illnesses. But do they?
Antioxidants and their health benefits have been the subject of more than 200,000 scientific publications since the 1940s. Over that time, researchers have concluded that antioxidants—including selenium, vitamins C and E, carotenoids like beta-carotene and the plant compounds known as flavonoids—indeed soak up the harmful free radical molecules our bodies produce and encounter over our lifetimes.

It’s less clear-cut, however, if they have any power to prevent or cure illnesses like cancer, heart disease and dementia. While research in the laboratory and in animal studies has shown consistently that antioxidants do good work, long-term dietary intervention studies in humans have produced conflicting findings.

Take the case of vitamin E. In 1993, an observational study of more than 87,000 female nurses suggested that vitamin E supplements could reduce the risk of heart disease by as much as 40 percent. Other observational studies provided similar evidence, but follow-up intervention studies have not been able to demonstrate the same benefit. One 2007 study, which followed women with cardiovascular disease or with a high-risk of getting it for nine years, found no benefit to taking vitamin E supplements.

The news has been disappointing for other antioxidant vitamins as well. A 2008 study that tracked almost 15,000 male physicians for a decade reported no differences in cancer or heart disease rates among those using vitamins E and C compared to those taking a placebo. The same year, a study of 35,000 men found that high doses of vitamin E and selenium did not lower the risk of prostate cancer. 

When the results of long-term clinical trials look like this, is it time to give up on antioxidants?

“I say, au contraire,” says Professor Jeffrey B. Blumberg, director of the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts, who suspects it’s the studies—not the antioxidants—that aren’t working. Blumberg takes issue with large-scale clinical trials that never screen for the subjects’ baseline levels of the nutrient in question. Maybe some people don’t respond to vitamin E supplements because they already consume adequate levels of the nutrient. “It’s like testing a hypertension drug without taking the baseline blood pressure,” he says.

Researchers, Blumberg suggests, also need to establish better thresholds—or how much the body actually needs—for each antioxidant before running trials. For example, what if researchers compared the health outcomes in people taking 40 units of a vitamin to those of people taking 400 units and found no difference between the groups? “Well, what if the threshold is 39?” he asks. “I do believe in the power of nutrition, but we’re not going to see it with this naïve approach.”

Newer fields like nutrigenomics and metabolomics are one way scientists—and eventually consumers—may get their arms around the question of whether antioxidants make a difference. “We now know that [vitamin E] probably worked for some people and didn’t for others. In a new age of personalized nutrition, we have capability to see how antioxidants affect individuals,” says Blumberg, a professor at the Friedman School of Nutrition Science and Policy.  

Bushels of Berries—and Evidence

But studies that pose the question “Does vitamin E reduce the risk of cardiovascular disease?” are taking the wrong approach, Blumberg argues. “The real question is, ‘In what way does vitamin E contribute to reducing the risk of CVD?’ ” he says, noting that there are dynamic interactions among the thousands of antioxidants, the bulk of which remain untested. The thousands of flavonoids, for example, react not just with each other, but also with the hundreds of carotenoids, the multiple versions of vitamins B and E, as well as the environment and genetics of each individual.

“There are so many variables,” says Blumberg. “We can’t invent a new way of doing science, but we can ask more sophisticated questions.”

For example, scientists recognize that when it comes to food, it seems the whole really may be greater than the sum of its parts. When James A. Joseph, who was a research physiologist in the HNRCA's neuroscience lab until he passed away in May, broke blueberry juice down to its component micronutrients and tested the antioxidant potency of each compound on its own, none was as powerful as the whole juice.

“The moral of the story is eat the berries," said Joseph, who gathered bushels of evidence that the antioxidant compounds in nuts and fruits can slow down the aging process in the brains of animals.

And eat a variety, too, says Blumberg. An all-blueberry diet devoid of leafy greens will provide you with more than enough of some kinds of phytochemicals but likely not enough of others. “They are all part of a complex defense network. You can’t substitute them for one another,” says Blumberg. “That’s like having a 10-foot wall, but leaving the gate open and the bridge across the moat.”

With that in mind, don’t expect an occasional glass of acai or pomegranate juice, which are heavily marketed as antioxidant-rich “superfruits,” will cover all the bases. The word “superfruit,” so often splashed across juice labels and the covers of glossy magazines, is both meaningless and misleading, says Blumberg.

With no scientific or regulatory definition, the term superfruit has become little more than a code word for “healthy,” the use of which the FDA does regulate. “To my knowledge, no one is even trying to define it—it’s too silly,” says Blumberg.

Moreover, Blumberg worries that deeming certain fruits and vegetables—usually exotic, expensive ones—“superfruits,” makes the more familiar apples and oranges seem like the Clark Kent of the produce section. The term “implies some fruits and vegetables are clearly much better than others. The science doesn’t support that,” says Blumberg. “What [we all] need to do is eat more fruit, period.”

Current guidelines recommend consuming two to four servings of fruit each day; most Americans barely get one. Blumberg is concerned that in an era when obesity is producing the first generation of children who are not as healthy as their parents, some people may believe a so-called superfruit can make up for the lack of fruits and vegetables in kids’ diets. “Consumers are being misinformed. All fruits are good,” he says. “The problem is we are not choosing them often enough.”

With new technologies and faster computers, scientists should be able to unravel the complexities of antioxidants. Whatever they find, it’s unlikely to conflict with that sage advice from mom: Eat your fruits and veggies.

This story first appeared in the Spring 2010 issue of Tufts Nutrition magazine.

Jacqueline Mitchell can be reached at jacqueline.mitchell@tufts.edu.

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