Map of life expectancy at birth from Global Education Project.

Tuesday, October 11, 2011

Less continues to be more ...

. . . or is it More continues to be less?

We should probably distinguish between two components of the so-called dietary supplements industry. Component number one, which gets a continual trashing at such worthy locations as Respectful Insolence and Science Based Medicine (which are not wholly separate entities, but that's by the way), is the "herbal remedy" or more accurately snake oil industry. This consists of companies that sell worthless products which they insinuate will cure your ills, but don't need to have any actual evidence because Congress has forbidden the FDA from regulating anything that's called a "dietary supplement" until and unless it comes to their attention that the stuff is actually killing or harming people, and they can prove it.

These are the people who claim to have the secret knowledge that "they," meaning mostly the pharmaceutical industry, don't want you to know about. Why these evildoers can't be prosecuted for fraud is unclear to me. Homeopathic remedies are in that class but so are echinacea, saw palmetto, etc.

Then there are products that really are dietary supplements, in the sense that they contain concentrated amounts of nutrients, such as vitamins and minerals, that we really do need in our diets. The purveyors of these products are usually more circumspect in their claims, partly because they are often big mainstream corporations some of which also produce FDA-approved pharmaceuticals. You'll see multivitamins advertised on TV, but the idea that they might do you some good is not as outlandish as the claims for shark cartilage and whatnot.

However, the claim largely seems to be untrue, at least for Americans who are almost universally adequately nourished. Just because a deficiency of a vitamin causes problems doesn't mean that more than enough is better. At one time there were indications from epidemiological studies that antioxidant vitamins might prolong healthy life but the more the issue has been studied, the less likely it seems. In fact, studies as time goes on and studies of higher quality are done, it has started to appear that most supplements may actually be harmful.

You may have heard about a recent publication by Jaakko Murso and colleagues in the Archives of Internal Medicine. This is helpful not only because it reports on new findings from a large-scale epidemiological study, but also because it contains a good review of the current state of knowledge to which this adds. The study included only older white women, so maybe it's different for other categories of Homo sapiens although it's not clear why it would be. And, like most previous studies of this question, it's purely observational. Randomized controlled trials of dietary supplements would be very difficult to do because you need decades of follow up and since they're sold over-the-counter there's really no way to control who takes them and who doesn't.

The difficulty with such studies is that whether people take supplements is not independent of other factors. Maybe people who take them are more health conscious generally, eat better, exercise more, don't smoke, drink only in moderation, yadda yadda. So they appear healthier but it's not because of the supplements. Or maybe people take supplements because they have health problems, so it looks like they're less healthy, but again it's not because of the supplements.

Sigh. All you can do is get as much information about the people as possible and throw it into a multivariate model. If you control for the smoking and obesity and pre-existing illnesses and what-not, you can at least argue that you might have been able to shake out the independent effect of the supplements.

What this study finds is pretty much in line from the picture that has already been emerging. It looks like calcium might be beneficial, but not if taken in excess. It looks like iron supplementation is harmful. This is actually the strongest finding because there is a consistent dose-response relationship, it's been observed in previous studies, and there is a plausible biological explanation for it. Anti-oxidant vitamins, it appears, are more likely to be slightly harmful than they are to be beneficial.

Again, this is all assuming you don't have a nutritional deficiency, but you almost certainly don't. We get everything we need, and usually more, from our diets. Can we absolutely rule out that multi-vitamins and mineral supplements might benefit some people under some circumstances? No, but there's no reason to believe it either. So why spend the money?

But for me, the point is not to give medical advice, which I am not doing. You should talk to your doctor. Rather, the point is that this stuff is heavily advertised, both to old people and to parents of young children (in the form of empty calorie cereal products with a vitamin pill thrown in, as well as actual pills), they're vacuuming up money, and it's essentially a scam. It shouldn't be allowed but the Supreme Court and Congress thinks corporations have a First Amendment right to lie to you. I don't think that was the Original Intent, Justice Roberts.

1 comment:

kathy a. said...

well, iron actually helps if one has anemia; calcium helps during development and if one has a predisposition to osteoporosis. but i guess that proves your point about talking to your doctor.