The Problem With Supplements

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Supplements are an example of how scientists interpret research in different ways, depending on point of view. Consider, for example, belief- and science-based approaches to vitamins.

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Two studies released this week provide additional evidence that vitamin supplements are potentially harmful and, at the very least, do no good.

This depressing news comes from the Iowa Women's Health Study. Older women in the study who took supplements ranging from multivitamins to high doses of single nutrients had a greater risk of dying than those who did not.

Equally depressing are the results of a trial of high-dose vitamin E and selenium versus prostate cancer. It found higher rates of the cancer among men taking vitamin E (selenium was somewhat protective). In this trial, it was so obvious that the supplements did not protect against prostate cancer that the investigators ended it before its scheduled date of completion.

USA Today interviewed me and Dr. Jeffrey Blumberg (Tufts University) about our interpretations of these trials.

I think that the main conclusion to be drawn from this research is that supplements do not make healthy people healthier. They may not cause harm at high doses, but they appear not to do good.

I don't take them and I don't recommend them -- except to people who have diagnosed nutrient deficiencies or other problems handling nutrients.

Dr. Blumberg, in contrast, thinks multivitamins constitute a useful nutrition insurance policy and everybody should be taking them.

Supplements are a good example of how scientists can interpret research in different ways, depending on point of view. I illustrate this point in Food Politics in a table in which I compare what I call "belief-based" (for lack of a better term) and "science-based" approaches to deciding whether supplements are needed, effective, or safe (see page 232).

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.

The statements in both approaches are true.

This is why point of view is such an important consideration in interpretation of nutrition research.

Image: Thirteen of Clubs/Flickr.

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This post also appears on Food Politics.

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Marion Nestle is a professor in the Department of Nutrition, Food Studies, and Public Health at New York University. She is the author of Food Politics, Safe Food, What to Eat, and Pet Food Politics. More

Nestle also holds appointments as Professor of Sociology at NYU and Visiting Professor of Nutritional Sciences at Cornell. She is the author of three prize-winning books: Food Politics: How the Food Industry Influences Nutrition and Health (revised edition, 2007), Safe Food: The Politics of Food Safety (2003), and What to Eat (2006). Her most recent book is Feed Your Pet Right: The Authoritative Guide to Feeding Your Dog and Cat. She writes the Food Matters column for The San Francisco Chronicle and blogs almost daily at Food Politics.

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