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Marion Nestle has an interesting blog post about the two most recent studies that fail to find benefits from taking vitamin supplements. (One study followed 38,772 women for 22 years, and found that those taking multivitamins or certain single vitamins were slightly more likely to die than those not taking any supplements; the other was a placebo-controlled trial of 35,533 men, which found that taking 400 IU per day of vitamin E increased the risk of prostate cancer during a 12-year follow-up.)
The reason I’m posting this isn’t that I think vitamins will kill you — the effects were small, and for the most part I think supplements tend to do nothing, rather than have big effects either way. Personally, I suspect that the most negative effect of vitamin supplements is the feeling of false healthiness they provide, which then allows you to justify making other, less healthy choices throughout the day.
Anyway, what I found most interesting in Nestle’s post was her explanation of two very different ways of looking at research into nutritional supplements — both of which rely on a collection of “true” statements, but reach opposite conclusions:
For example, on the need for supplements, a belief-based approach rests on:
- Diets do not always follow dietary recommendations.
- Foods grown on depleted soils lack essential nutrients.
- Pollution and stressful living conditions increase nutrient requirements.
- Cooking destroys essential nutrients.
- Nutrient-related physiological functions decline with age.
A science-based approach considers:
- Food is sufficient to meet nutrient needs.
- Foods provide nutrients and other valuable substances not present in supplements.
- People who take supplements are better educated and wealthier: they are healthier whether or not they take supplements.
I’m not sure I quite agree with her labels (“belief-based” and “science-based”), but I definitely see these patterns of thinking in discussions of pretty much all areas of health and exercise research. The first set of statements makes a strong case that it’s plausible that supplements could improve health — but it leaves out the final step, which is to show that they do improve health. Similarly, the second set of statements explains why we shouldn’t be surprised if supplements don’t improve health, but doesn’t prove it. So to me, neither of these two approaches is satisfying — because the debate should be settled empirically.
Of course, research is complicated, and in many health debates it’s difficult to agree on what constitutes empirical evidence. That’s less and less true in the case of vitamin supplements, though. Study after study fails to find any benefits, so the hypotheses of the “belief-based” approach seem emptier and emptier to me.