Biology in the News Explained

Don’t take multivitamins during chemotherapy

Antioxidants have received another strike against them. Normally, this blog would be the first to caution that a controlled study is needed to provide information that is at all conclusive, and the gist of the article at is that clearly in this case those studies have yet to be done.

However, as in most pharmaceutical situations, the conservative action is not to take the extra drug (whether it be novel chemical or “essential” vitamin), because although we think we know that anything marketed as a supplement must be good for us, this is by no means the case. We still know next to nothing about how the human body works even when we’re not messing with it by adding supplements to the mix.

The idea behind the latest caution is that chemotherapy works to destroy cancer cells through the creation of reactive oxygen species (ROS – of which the infamous “free radicals” are a major type). So, if the body is flooded with extreme amounts of antioxidants such as vitamins C and E, it is possible the chemo will not be as effective.

Of course, the flip side of this is that perhaps the antioxidants protect non-cancer cells, which could reduce side-effects associated with chemotherapy. But any strongly positive effect has yet to be established (although see this abstract showing potentially mixed effects), and if you are protecting cancer cells along with the cells you like, really what is the point of chemotherapy in the first place? (A cynical answer to this question can actually be found on this site, but it is not really relevant to the question at hand.)

What data we do have continue to challenge the popular notion that massive supplement use is beneficial. When we introduce large amounts of a chemical into our bodies, even chemicals we know can have a useful function at much lower levels (“too much of a good thing” applies pretty much to anything we ingest, even water), we are creating a novel environment to which humans have not had a chance to respond evolutionarily. Logically, the chances that interfering with more natural bodily functions in this way will create problems are much, much higher than the chances that we are smugly improving on nature.

Although cancer treatment is a special case that has yet to be definitively tested, the logic of the doctors concerned about the practice of massive antioxidant use during treatment cannot be denied. And the negative effects of antioxidants on exercise physiology are not likely to be a special case.

So do yourself a favor, even if you are lucky enough not to be someone undergoing chemotherapy at this moment: lay off the supplements, and eat your vegetables.


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