This post is a follow-up to the earlier post on systematic reviews and the Cochrane organisation

If you are looking to spice up the discussion at dinner this week, you might want to drop this little bombshell. There was a theory once, that given that antioxidant molecules at the cellular level can act to remove free radicals that induce cell damage, that eating supplements with antioxidants might have beneficial health effects, especially on aging related problems like heart attacks, or on cancer.

And indeed, some trials were performed that seemed to confirm this. However, they were small and not particularly conclusive. (See our post on Collecting Enough Evidence to see how you can use DataClassroom to illustrate what this means in practice).

When you read articles about food or supplements in the media, you’d be forgiven for getting the impression that antioxidants had been proven to be both helpful and not dangerous. Right?

Wrong!

When finally a large, definitive trial took place with many participants, no benefits were seen, and indeed the trial revealed harmful effects - participants taking antioxidants died more often than the control group. You can see the published trial, called “CARET” on PUBMED here - it concludes that patients on the pills had “excess lung cancer incidence and mortality”. Ouch!

Since then, Cochrane (see our earlier blogpost here) have performed a large systematic review, weighting the results from many trials, and the conclusion is indeed that, on balance, taking antioxidant supplements has a small but significant harmful effect. You can read the full review on the Cochrane website here.

The author’s conclusions were (my highlights): “We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.”

It just seems that that recommendation about marketing hasn’t got through to many marketing departments yet…!

Why this is important

Maybe it’s not such bad news after all. It does after all mean you don’t need to feel you should spend money on supplements that aren’t going to help you!

But that’s really a side issue. The real revelation is that things are often a lot more complicated and subtle than one might expect, and that the scientific process is one of moving ever closer to the truth, and being willing to accept new conclusions based on new evidence.

Here’s hoping you have a good discussion at dinner!

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