This was published in Scientific American Food Matters on February 23, 2015
There appears to be a continued public misconception (encouraged by the supplement industry) that free radicals are bad, and that antioxidants are good. Of course, like most phenomena affecting our health, it’s not that simple.
Free radicals are molecules or atoms containing an unpaired electron. Unpaired electrons are attention seekers. They really don’t like being alone, so are always searching out other electrons. This makes them highly reactive. Free radicals are like the unstable friend who shows up drunk to the party and starts breaking things. Antioxidants are molecules that are able to donate an electron to the free radical, thus stabilizing it. They’re like the patient friend who is able to convince the free radical not to drive home, takes him to the back room to calm him down, and brings him water and a bucket once he starts throwing up.
Needless to say, without the presence of antioxidants, free radicals can really ruin the party. The cellular damage that results is called oxidative stress, and is associated with ageing, heart failure, cancer, Alzheimer’s, and many other health problems.
Until recently, the thinking had been that the more antioxidants, the less oxidative stress, because all of those lonely electrons would quickly get paired up before they had the chance to start mucking things up in our cells. But that thinking has changed.
Drs. Cleva Villanueva and Robert Kross published a 2012 review titled “Antioxidant-Induced Stress” in the International Journal of Molecular Sciences. We spoke via Skype about the shifting understanding of antioxidants.
“Free radicals are not really the bad ones or antioxidants the good ones.” Villanueva told me. Their paper explains the process by which antioxidants themselves become reactive, after donating an electron to a free radical. But, in cases when a variety of antioxidants are present, like the way they come naturally in our food, they can act as a cascading buffer for each other as they in turn give up electrons to newly reactive molecules.
“For instance,” Villanueva said, “chocolate has more than 20 antioxidant flavonoids. One is converted into a free radical and becomes reactive, but less reactive [than the first]. It then reacts with another, and that one is less reactive and so on and so forth, and all of them react with each other, decreasing the damage that would be happening to our lipids, or proteins or DNA”
If there is only one type of antioxidant present, say in the case of a high-dose vitamin C supplement, then there are no other antioxidants to provide that protective cascade effect. Then you could end up with a bunch of reactive vitamin C, which itself can cause what they call “antioxidant stress.”
Wait a minute—So a person taking high dose antioxidants might actually be doing the exact opposite of what he or she is trying to accomplish with the supplement? I asked. Yes, they said. But it gets even worse.
Free radicals are a natural byproduct of aerobic metabolism in the cells (energy production using oxygen), which ramps up during physical activity. The free radicals produced by this increase in metabolism signal the cell to make its own home-made antioxidants. These endogenous antioxidants are very important, and may be responsible for many of the health benefits associated with physical activity.
A 2014 review published in Nutrition and Food Science called for more research on the subject, but ultimately concluded that high-dose antioxidant supplements can effectively “abolish the beneficial effects of exercise” (emphasis mine). Researchers think that high levels of a single antioxidant (like the 1,000 mg of vitamin C in a packet of Emergen-C) can snatch up all the free radicals produced by exercise before they have a chance to trigger the synthesis of those beneficial endogenous antioxidants.
Barbara Demmig-Adams, professor of ecology and evolutionary biology at the University of Colorado in Boulder, and one of the authors of the 2014 paper wrote in an email:
“I think it’s a really important realization that the much-maligned radicals have a job to do in our bodies and that single high-dose supplements can do more harm than good. . . Our review on antioxidants and exercise is just the tip of the iceberg. There is a real paradigm shift . . . in the biomedical research area that is causing pioneers to ask, ‘could 50 years of research be wrong?’”
It didn’t take much Googling to discover that over the last few years, this new thinking about antioxidants has indeed enjoyed some coverage. But has this new knowledge really made it through to the public? In a highly unscientific survey, I annoyed my friends over the last few weeks by baiting them with the question: “So what do you think of antioxidants?” Generally the consensus still seemed to be that a vitamin C supplement, say before a cold, was a good idea.
“The best advice is just to eat a proper diet that contains a variety of antioxidants, but don’t go overboard,” said Robert Kross. “Antioxidant supplements are only justified if you have a deficiency,” he explained. The research continues to support this idea—that optimal health comes from moderation and balance. But will we ever really embrace moderation?
Catherine Price wrote the book “Vitamania: Our Obsessive Quest for Nutritional Perfection.” (available Feb. 24)
“We want a hero and a villain,” she told me over the phone. “But it’s actually more about balance. Sometimes [antioxidants] are good, and sometimes [they’re] not good. What are we supposed to do with that?” It’s especially hard for people to wrap their minds around the latest nutrition advice, Price pointed out, because it always seems to be changing.
“It’s so confusing. It speaks to our inability to cope with the uncertainty of science. You have experts for 30 or 40 years saying that margarine is good for us, and then we find that it’s totally untrue, and still there are all these other questions for which we don’t have the answers,” said Price.
So whom should we expect the public to listen to, when we righteously start touting the latest data? By their very nature, scientists are never 100 percent sure about anything. But marketers seem to be so certain about everything they tell us. Not only that, but their messages are simple, and make us feel good:
Vitamin C is an antioxidant.
Antioxidants are good for you.
Drink this, it will make you feel better.
In fact, in the long run, it might make you feel a whole lot worse. Our cells practice an elegant balancing act, each component playing an important part: vitamins, minerals, electrolytes, water, free radicals, other metabolites, antioxidants—both endogenous and dietary. When we figure out a specific beneficial role any one of these serves, it’s tempting to say: “Wow, look how important this thing is, let’s make sure folks get a whole bunch of it!” But that can throw off the whole delicate system, leading to some serious consequences.
We still have much to learn, but here’s a safe bet: usually when something is over 1000 percent of the recommended daily value, it’s probably best to just leave it on the store shelf.