A study published yesterday in the Archives of Internal Medicine investigated the link between taking dietary supplements and an increased risk of death in older women.
Associate Professor Ian Chapman from the University of Adelaide explains the methodology and results of the study.
This article examines the Iowa Women’s Health Study, which began in 1986, and examines death or death rates through 2008.
The average follow-up period was 19 years for each person. Subjects were older postmenopausal women with an average age of 61 at the start of the study.
I don’t know if this is a great article because there are so many variables that the authors corrected for: there were clear differences between the women who took the supplements and those who didn’t initially.
Women who took the supplements were more likely to be non-smokers; they were twice as likely to take hormone replacement therapy (HRT); they had higher levels of education and lower body mass index; and they were more physically active.
Moreover, they were different for each measure of food intake reported in the article.
The authors attempted to correct for these differences with their analyzes and found some effects of the supplements.
But I can’t find the absolute death rate in the paper in either of the two groups before the authors started their corrections. And you should be wary when people make corrections for a variety of variables.
These are statistical corrections and there are ways to make them, but they don’t take into account the underlying factors.
Women who are not feeling well, for example, can start taking multivitamins or minerals. And they could die because they weren’t well, not because of the multi-vitamins or the minerals.
This type of factor is not taken into account in these multivariate analyses.
The link with iron supplements and mortality is the strongest. Why would older women take iron supplements?
I assume the women were taking iron supplements because they were iron deficient, which may be related to bleeding. It is the most common cause of iron deficiency and anemia.
In a postmenopausal woman, this is likely due to gastrointestinal bleeding or some postmenopausal uterine bleeding. Now neither of these is good and both could reflect a negative result anyway.
In fact, the supplements could address the thing that causes these women to have an increased death rate.
Alternatively, iron can be given non-specifically for anemia without the women necessarily being iron deficient.
High body iron stores have been associated with increased rates of cardiovascular events in some studies. The link between increased mortality and iron supplementation appears to be quite strong in the analyses. Iron appears to be associated with an increased death rate, while calcium is linked to a reduced death rate.
These are two of the strongest conclusions of the article.
What other studies have concluded about taking supplements?
There have been a number of such studies – population-based prospective cross-sectional studies rather than randomized controlled trials.
Most of them show no great mortality or welfare benefit from taking minerals or multivitamins in the absence of a well-defined deficiency syndrome.
Meta-analyses have recently suggested that vitamin D supplements for older people might help them live a bit longer, but there really isn’t a whole lot of evidence.
And, in some circumstances, there is even evidence of harm. Overall, there may be more evidence for harm than good, especially if certain supplements are taken in large amounts.
In particular, some antioxidants, such as vitamins E and A, can cause harm if taken in excess.
Why is it so difficult to get a clear picture of vitamin and mineral supplements?
The problem with all of these studies is that they are not strictly speaking randomized controlled trials.
That’s because the latter are really hard to do: different people in the control group will go off and take multi-vitamins and minerals on the side – how do you control that?
And you have to do a study for a number of years. This study had an average follow-up of 19 years in nearly 40,000 women. Ideally, we should take a group of people and randomly divide them into groups that may or may not contain minerals and vitamins, and then follow them to see what happens.
It would be extremely difficult to conduct such a large study for such a long time in a randomized, controlled fashion.
So we have studies like this one that use varied data that have to be adjusted, and the authors end up saying, when we’ve made all these adjustments, we end up with this result.
What should we take away from this study?
The proof of the study is that you don’t live longer taking multi-vitamins and minerals, with the possible exception of calcium.
Whether or not there is harm I think is another matter and I wouldn’t rely too much on this document to draw evidence from it.
The article and editorial associated with this study do not support the use of supplements in healthy people who have no known impairments and who are not taking medications or have a disease that could cause it. And I wouldn’t recommend them either.
