Supplement Showdown: A Look at Vitamins and the Fight Against Cancer

Q: What vitamins and supplements have been shown to fight cancer, and which ones are dangerous and should be avoided?

A: As long as we’ve known about vitamins, we’ve explored the idea that they might play a role in cancer prevention.

As an oncologist involved in cancer care over the long term, I can remember when Dr. Linus Pauling, a highly regarded scientist, advocated that vitamin C prevented cancer; however, confirming evidence to support his theory didn’t materialize. Some folks still believe it has value, and have done research showing that intravenous, rather than oral, administration of vitamin C might be more effective in killing cancer cells.

Sometimes a study is done in which the secondary outcomes — not the primary focus of the research — seem to indicate that a vitamin can help prevent a particular type of cancer. Unfortunately, time and again, when scientists look at the issue specifically and do focused research on a vitamin, the theory doesn’t hold up.

For instance, studies have been done in the past to verify theories that beta-carotene would decrease the risk for lung cancer, and that vitamin E and selenium would protect against prostate cancer. Unfortunately, those studies showed that the supplements actually increased the risk for some and provided no meaningful benefit for many.

There are also experts who believe quite strongly that vitamin D prevents some cancers, but the Institute of Medicine has concluded that it hasn’t been shown based on what we know today. Having said that, there’s a clinical trial underway that, hopefully, will shed some light on the issue.

A lot of people believe in vitamins — especially since it’s a lot easier to take a vitamin than to eat a healthy diet or engage in other behaviors that decrease the risk of cancer. There are also many people who believe in nutritional supplements, but once again, caution must be used.

The Food and Drug Administration came out recently with a list of 14 companies it had contacted with a directive to cease and desist marketing their supplements as anticancer treatments. Many folks believe these claims, but, unfortunately, too often, the promises are based on stories and not on evidence — and it is evidence that counts.

It’s important, if you are undergoing cancer treatment, that you share with your health professional a complete list of everything you’re taking. This can be a way of avoiding problems, as some supplements — fish oils, for example — have been shown to interfere with certain chemotherapy drugs. The list of vitamins and supplements available to all of us is long, and knowing how each of them can affect cancer treatment is difficult. Fortunately, pharmacists and health professionals have access to computerized systems that can evaluate the potential for any serious drug interactions — and that’s good, because this software provides way more information than any one health professional or patient would routinely know.

Cancer can be a terrible disease, and any of us are vulnerable to promises of miracle cures. We all want to believe the stories of incredible responses to simple nostrums. Sadly, experience has taught us that we must be very careful about falling victim to claims that are not evidence-based.

We must always remember that anecdotes are not evidence. They frequently come from well-meaning people who believe something happened, but when you look carefully, you’ll often find that the details don’t support the claims.

If only it were that simple: We would have cured diseases like cancer a thousand times over.

Len Lichtenfeld, M.D., is deputy chief medical officer of the American Cancer Society.

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