Multi-Vitamin study- Be careful what you read

Dr. Brenda Gill
By Dr. Brenda Gill
October 24th, 2011

There was a recent study on multi-vitamins causing concern that was reported in the news that needs clarification. The study “Dietary Supplements and Mortality Rate in Older Women” was an analysis of data from 38,772 post-menopausal women in the Iowa Women’s Heath Study. The data was obtained through a self-administered questionnaire that started in 1986 with two follow-up questionnaires in 1997 and 2004.

The questionnaires asked about lifestyle practices, food intake, dietary supplement use, weight, smoking status, hormone replacement therapy and the presence of diabetes or heart disease. 


Although the study asked about their intake of dietary supplements, it did not ask what or how much of any specific nutrient was taken, what form the supplement was taken in, or the type and quality of the supplement taken. As well, although the women were asked whether they took a “multi-vitamin”, the study did not define it—was it a multi-mineral, vitamin and/or plant combination? Also, there was no verification of the accuracy of the answers provided in the questionnaires, and the women were not asked why they were taking the supplements or the impact of taking or not taking the supplements.

It was not tracked whether the women started the multi-vitamin after they had diabetes or heart disease or before and whether they stopped or started it. It is not uncommon for a person to start a multi-vitamin after being diagnosed with a serious condition, such as diabetes or heart disease. If this was the case and the person died because of the underlying disease, the death would be attributed to the disease and the multi-vitamin “associated” with the death.  So, you can see how information can be mis-interpreted.

The study was a “retrospective” study of already collected information. It was not a “clinical trial” where persons were given a specific dietary supplement or a placebo and then followed over a period of time to see specific outcomes of the study and factors contributing to those outcomes.  Individual circumstances change over time, and probably the women in this study changed, stopped or started new dietary supplement regimens over the 18 years and there was no direct contact with the participants.

Therefore, there was insufficient data from the study to make any conclusion about the impact of multi-vitamins on mortality. There are thousands if not tens of thousands of different combinations of vitamins, minerals and herbs that could be considered a “multi-vitamin”. Also, quality, concentration, dosage would also vary. Studies, in which people are asked to recall years of dietary habits or supplement use are often inaccurate. The only conclusion that may be drawn is a “slight statistical association based on a limited data set of questionable reliability—and a simple association does not reflect causation”  (Thorne Research). Even the study’s authors stated “It is not advisable to make a causal statement of excess risk based on these observational data”!

This is just another example of information taken from a study taken out of context, mis- interpreted and sensationalized by the media. More time and energy should be devoted to report on significant, helpful information useful to the public that will enhance health and well-being of all.

Dietary supplements, when made by a quality manufacturer, recommended by a knowledgeable health-care practitioner and taken for the appropriate use can promote, enhance, support and help maintain overall health and well-being. 

Brenda Gill is a naturopath practising in Nelson and Rossland, BC.

Categories: Health

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