Antioxidants and cancer: questions about quercetin

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Another development in the continuing saga of confusion about the benefits and hazards of antioxidant supplements. Despite recent suggestions that certain antioxidant supplements may slow or counteract some of the benefits of exercise, there’s still great interest in whether plant-based antioxidants like quercetin can boost endurance. A new study in the Journal of Agricultural and Food Sciences should make you think twice about whether you really want to pursue that avenue.

Kuan-Chou Chen, Robert Peng, and colleagues note that vegetables, fruits, and other plant-based foods are rich in antioxidants that appear to fight cancer, diabetes, heart disease, and other disorders. Among those antioxidants is quercetin, especially abundant in onions and black tea, and ferulic acid, found in corn, tomatoes, and rice bran…

They found that diabetic laboratory rats fed either quercetin or ferulic acid developed more advanced forms of kidney cancer, and concluded the two antioxidants appear to aggravate or possibly cause kidney cancer.

I generally try to avoid putting too much emphasis on single studies like this one (especially when they’re conducted on “diabetic laboratory rats” instead of humans), since it’s very frustrating to be bombarded by messages that bounce back and forth between “X is great for you” and “X is bad for you” and “No wait, X will make you stronger” and “Oops, sorry, X will kill you.” I definitely don’t view this as anywhere near definitive evidence that quercetin will kill you.

That being said, this study does fit into a larger pattern of research over the past few years that leaves me with the conclusion that we’re much better off getting our micronutrients from whole foods than from supplements. I know, I know, that’s difficult. In fact, after I blogged about Juice Plus+ last month, I got an e-mail from a promoter of the product who made that argument:

If you are like me, you probably love eating the real thing, and nothing beats the flavour of fresh produce. I just had some corn, peaches and grapes! But it’s practically impossible to eat 13-17 servings every day, especially fresh, vine ripened and raw.

I don’t know — “impossible” seems like a bit of an overstatement. And I’m not sure where “fresh, vine ripened and raw” came from. Frozen and canned fruit and vegetables still seem like a far better option to me than supplements. Here’s what Lauren and I picked up in two trips to the fruit and vegetable market in Sydney last summer, for ridiculously low prices ($5 for 12 baskets of strawberries, $5 for that entire crate of plums, etc.). Most of it ended up in our freezer — which was pretty awesome over the winter!