Antioxidant Alarm Bells
A new study suggests that antioxidants may not be as beneficial as previously thought, but experts question the results.
By December 10, 2004 - last reviewed on June 9, 2016published
The news made the rounds of health publications last month like a nutritionist's version of a Hollywood breakup rumor: antioxidants don't prevent cancer, and they might even cause death in some cases. But like a breakup rumor, the latest antioxidant scandal relies on shaky evidence. Once you understand the source of the scandal, the marriage of antioxidants and health looks as strong as ever.
It begins with a recent paper published in the British journal The Lancet, in which scientists combined data from past medical trials to see how many people taking antioxidant supplements got gastrointestinal cancer or died of any cause, compared with people taking placebo pills. The combined data showed that taking antioxidant supplements didn't dent the risk of gastrointestinal cancer. In fact, a subset of high-quality trials showed that taking antioxidant supplements was associated with an increased risk of death.
One thing to note right away is that the researchers investigated only high-dose antioxidant supplements, not antioxidants found in food. So their analysis doesn't give you any excuse not to eat your greens.
Antioxidants-special vitamins, minerals, and plant chemicals found in fruits and vegetables-are still believed to be a very important part of a balanced diet. They neutralize free radicals of oxygen, which damage cells. Previous studies suggest that antioxidant-rich diets may help reduce the risk of not just cancer but mental decline and psychological distress.
Antioxidants like vitamin E may snag some free radicals before they can harm brain cells, thereby reducing the risk of age-related mental decline. Vitamin C, our favorite cold-buster, may also bust stress, and polyphenols may help maintain positive mood states. And you don't have to swallow a bitter pill to get these benefits. Vitamin C shows up in everything from blueberries to potatoes, vitamin E in almonds and leafy greens, and polyphenols in green tea and red wine.
The new findings on antioxidant supplements are not nearly as dire as they first appear, insists Jeffrey Blumberg, professor of nutrition at Tufts University.
First, the researchers combined data about different kinds of antioxidants: beta-carotene, vitamin A, vitamin C, vitamin E, and selenium. According to Blumberg, the results from studies about different antioxidants just aren't combinable. "Antioxidants are qualitatively and quantitatively different from on another," he says. "You can't substitute one for the other." For instance, vitamin C cures scurvy, but vitamin A doesn't. That doesn't mean that vitamin A is always bad; it's just not vitamin C.
Second, says Blumberg, the results were skewed by one unusual trial. Alone, the other trials showed that antioxidants don't affect the risk of death. They even tend to reduce the risk, though not enough for statistical significance. The unusual trial drove all the other data so that they showed a just-barely significant increase in the risk of death. Not only is it inappropriate to draw a conclusion based on one trial, Blumberg notes, but this one trial included only people who had been exposed to asbestos or who had smoked a pack a day for 30 years.
"The jury is still out," Blumberg says, on the exact benefits of antioxidant supplements. They may prove effective against some diseases but not others. He points to promising research on macular degeneration, cardiovascular disease and Alzheimer's disease. Blumberg also remarks that the very paper that caused all the controversy actually revealed beneficial effects of the mineral supplement selenium on gastrointestinal cancer.
The real story is that you should eat a healthy diet full of antioxidant-heavy fruits and vegetables. Far from breaking up with your broccoli, make sure that you have steady dinner date with it.