Facts and myths about antioxidants and cancer
May 02, 2014
Some of the most popular misconceptions surrounding cancer, cancer prevention and cancer treatment are about the role of antioxidants. Like many of the popular myths about cancer, there are facts, half-facts and outright falsehoods.
Fact: Damage to genes, particularly those involved in the regulation of cell division and cell death, is the key event in the development of cancer.
Fact: Oxidants are substances, most often generated by our own body, that cause damage to chemicals, including the DNA that makes up our genes, by oxidizing them. The oxidation reaction most familiar to us is when metal rusts.
Fact: Our bodies’ oxidants can contribute to cancer.
Half-fact: Antioxidants are chemicals we ingest that then run around neutralizing oxidants, rendering them powerless to promote cancer. The so-called antioxidant vitamins, of which vitamin C, E, and beta-carotene are the most well known are more properly called redox agents. In a particular environment, they prevent or reverse oxidation, called reduction. But they may change the acidity or even just the concentrations of the components of the reaction, and they may facilitate just the opposite. For example, vitamin C in a patient with normal iron levels is an antioxidant. But take a patient who has been transfused over and over to the point of iron overload, and vitamin C becomes a pro-oxidant and high doses can precipitate heart failure from oxidation.
Fact: When population studies have looked at diet and cancer, people who eat foods high in antioxidants (predominantly vegetables and fruits) develop less cancer than people who don’t.
Myth: Taking supplements with antioxidants will prevent cancer.
It would seem only a small theoretical leap to assume that vitamin supplements rich in C, E, and beta-carotene would accomplish what a good diet will do, and a pill seems oh so much easier, too.
There have been four studies that have looked at antioxidants and cancer prevention. The first study was done in China. It looked at the incidence of stomach cancer in a population where it is very prevalent and gave half of the villagers vitamin E, beta-carotene, and selenium. They got less stomach cancer than the half without the supplement.
This success led to two more studies. One was a U.S. study looking at prevention of breast cancer. Anti-oxidant supplements seemed to offer no benefit. Then there was the Finnish study looking at vitamins E, C, and beta-carotene in the prevention of lung cancer in smokers. The number of patients getting lung cancer in the antioxidant arm was 18% higher than in those without the supplements. The death rate was 8% higher. At the time, researchers scoffed at this result, but the study was repeated with the same result here in the U.S. They actually quit the study early in order prevent endangering the health of the antioxidant group. It would appear that these doses in those patients, these particular antioxidants may no longer be antioxidants, but instead pro-oxidants. At least that is one hypothesis.
Bigger Myth: Antioxidants can treat cancer.
If preventing cancer with supplements was a little theoretical leap, this is a huge one. There is no logical reason to believe that once damage has already occurred and a cancer has developed that antioxidants can reverse the damage or otherwise change the course of the cancer.
Half-fact: Antioxidants can prevent chemotherapy side effects.
Some chemotherapy agents, such as adriamycin, set off a cascade of oxidants. Some of its side effects, particularly an effect to weaken heart muscle, may be decreased with antioxidants. But some of its anti-cancer effect may be through oxidation pathways as well. In fact, a powerful antioxidant medication we sometimes use to make it safe for patients receiving lots of adriamycin over time also decreases its effectiveness. It could be a mistake for a patient with a strong heart, receiving a limited dose of adriamycin, to take antioxidant supplements.
The data about antioxidants would suggest that the surest way to limit our cancer risk is to make changes in our diet. It is probably a testament to the successes of modern medicine that we are, instead, so willing to turn to a pill – better yet if we can spend money on a dietary supplement or a vitamin. But if you want my advice, I would echo something we all heard from our mothers; “Save your money” and “Eat your vegetables.”