Beta Carotene Pills: Might Help, Might Hurt
For: Ask the Experts, May 2002
Readers sometimes ask us: why does the WELLNESS LETTER advise against taking certain dietary supplements when these "can't hurt and might help"? The fact is, for most supplements, there's little solid evidence for "can't hurt"—or, indeed, for "might help." We're not talking about obvious immediate adverse effects, which are usually well known, but rather long-term harm, such as liver damage over months or an increased risk of cancer over years, which can be determined only by long, large, well-designed studies. Beta carotene provides a good lesson, especially because it was a star among supplements.
There was good research—mostly involving beta carotene from the diet—suggesting that this vitamin-like substance could lower the risk of cancer and possibly other diseases. And there was no evidence of adverse effects: the worst thing large amounts of beta carotene could do, it seemed, is turn your skin slightly yellow or orange, which is harmless. Thus, many nutrition experts—including briefly the WELLNESS LETTER—jumped on the bandwagon and recommended beta carotene pills. Then came two first-rate studies showing that beta carotene supplements could cause serious harm, at least in smokers. Since then, scientists have been trying to explain what went wrong with beta carotene, and recently some interesting theories have emerged.
Unpredictable effects of antioxidants
This brings us back to the complicated world of antioxidants, which includes beta carotene, as well as vitamins C and E, other carotenoids, and many other phytochemicals (plant chemicals). Antioxidants help deactivate free radicals, unstable molecules that are by-products of cells "burning" oxygen for energy. Free radicals can damage the basic structure of cells and thus lead to chronic diseases (notably cancer and heart disease) and accelerate the aging process. Plants are vital sources of antioxidants for humans and other animals. In addition, hundreds of dietary supplements now trumpet the antioxidants they contain.
There are many types of antioxidants, and they do different kinds of work. What marketers of supplements never tell you is that not all of it is good work. Antioxidants can certainly deactivate free radicals in a test tube, but in the human body they can sometimes have the opposite effect—acting as prooxidants (see below) instead of antioxidants. That's what the two beta carotene studies showed.
Published in 1996, the CARET study (full name: Beta Carotene and Retinol Efficacy Trial) tested beta carotene and vitamin A supplements in people at high risk for lung cancer—smokers, former smokers, and asbestos-industry workers. The study was halted when it became clear that those taking beta carotene (not even a high dose—just 30 milligrams a day) actually had a higher rate of lung cancer and higher mortality rate than those taking a placebo. The supplements increased the risks only in those who smoked more than a pack a day and/or drank "above-average" amounts of alcohol. The other study, a large Finnish one published two years earlier, yielded similar results.
Smoking was the problem this time...
Why are smoking and beta carotene pills a dangerous mix? The problem is partly the smoking, partly the beta carotene, and partly the oxygen-rich environment of the lungs. Beta carotene is oxidized as it inactivates the free radicals from cigarette smoke, and its antioxidant capacity is "used up." In the process, it can turn into a pro-oxidant or form oxidized by-products, particularly if adequate amounts of vitamins C and E aren't present. It's well known that C and E work together to produce their antioxidant effect. Recent research strongly suggests that these vitamins can also help limit the oxidation of beta carotene and/or recycle it after it is oxidized, so that it won't damage cells. (In fact, any antioxidant can become a pro-oxidant under certain conditions in the body—especially if other antioxidants are lacking, since they protect one another from oxidation.)
Making matters still worse for smokers is the fact that they have low blood levels of vitamin C, so the supplemental beta carotene doesn't have enough C to work with. This scenario puts smokers at increased risk for the oxidative damage that is believed to contribute to cancer. And there are still other theories about how high doses of isolated beta carotene, taken over the long term, might increase the risk of cancer in smokers.
Morals of the story
• Don't assume that any supplement "can't hurt, might help" or that antioxidants are always beneficial. The nutrients and other healthful compounds in foods work in a fine balance, which scientists are only beginning to understand. There's also a delicate balance between free radicals and antioxidants in the body. Smoking was the complicating factor with beta carotene, but who knows what factor (sun exposure, alcohol, medication, intense exercise, or a previous diagnosis of cancer, for example) might make supplement X, Y, or Z dangerous?• Don't smoke.
• Don't take beta carotene pills if you smoke, are a former smoker, or are a heavy drinker.
• Eat lots of fruits and vegetables. Even if you don't smoke, it's better to get beta carotene from food (carrots, spinach, cantaloupe, etc.) than from pills. There has never been any evidence that the beta carotene in foods poses any danger, perhaps because it comes with many other plant chemicals that all work together. In fact, virtually every study shows that foods rich in beta carotene help keep people healthy—and even reduce the risk of lung cancer.
• The only supplements we recommend are vitamins C and E (250 to 500 milligrams of C; 200 to 800 IU of E); calcium if you don't consume lots of dairy products; and, for many people, a basic multivitamin/mineral (which contains 400 micrograms of folic acid). Few people get that much C from their diet; it's nearly impossible to get that much E from food. A large body of evidence indicates that these doses of C and E are not only safe, but also likely to help keep you healthy. Make sure you take C and E, not just one of them, since they work together and protect each other from oxidation.
UC Berkeley Wellness Letter, March 2000
