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After Friday’s column on probiotics, vitamin D and ZMA, I received a very interesting e-mail from Reinhold Vieth, a University of Toronto professor who is one of the world’s leading experts on vitamin D, and who has also conducted research on probiotics. It’s never good news to get an e-mail from a respected researcher who says that, on the topics on which he is an expert, “I came to verdicts opposite to yours today.”
For probiotics, which I came down in favour of, he pointed out weaknesses such as small sample size in the very few existing studies. For vitamin D, he pointed out the undeniable fact that, in a recent study, supplementation improved athletic markers such as jumping in adolescent girls, 75 percent of whom turned out to have below-recommended levels of vitamin D. And that’s far from the only relevant study.
These are excellent points, which require a bit of explanation/hair-splitting. For general health and wellness, the evidence in favour of vitamin D is orders of magnitude stronger than the evidence for probiotics. I would urge everyone to be very aware of whether they’re getting enough vitamin D. Probiotics, on the other hand, can be safely ignored — they might help you, but it’s no big deal if you don’t think about them.
But if we’re examing these substances as sports supplements rather than simply as supplements in general, as the Jockology column aimed to do, the criteria are a little different. Vitamin D is great — but if 75 percent of adolescent girls are deficient, that means we all should consider taking it, not just athletes or exercisers. The evidence for probiotics is weaker, but what little evidence there is suggests it helps athletes (or others whose bodies are being heavily stressed) more than the general population. In fact, there’s some reason to believe it’s only of benefit to athletes who are training at a very high level of intensity.
So… two different conclusions, both valid — and confirmation that applying labels like “true” and “false” to complex research questions almost always leads to oversimplification.