Do nutritional supplements increase risk of death?

  • 14 Oct 2011
  • Reading time 4 mins
Read later

Headlines rang out over the UK that taking vitamins might very slightly increase risk of death of older women. It is based on a survey of over 38,000 women in Iowa, surveyed three times over three decades. What does the study actually show?

Contrary to the headlines, this recent paper, published in the journal Annals of Internal Medicine, analysed the risk of mortality of those taking various supplements versus non-users and found that supplement takers had a reduced risk of death. To quote the study “self-reported use of vitamin B complex; vitamins C, D, and E; and calcium had significantly lower risk of total mortality compared with non-use; copper was associated with higher risk.” They found statistically significant health benefits for many supplements, with calcium being the strongest positive, and copper being the strongest negative.

When they looked at the pattern of risk over the three decades they reported that, for many nutrients the mortality risk was less in supplement takers and further reduced the longer people had been taking the supplements. This was true for multivitamins, magnesium, selenium, vitamin D, vitamin E. Vitamin C and B vitamins were associated with reduced risk in each of the three survey points. The most negative association was seen with iron, with increasing mortality risk the longer a person had taken it. Copper went from a negative in the first survey point, to a positive result in the last. They also found that “compared with nonusers, supplement users had a lower prevalence of diabetes mellitus, high blood pressure, and smoking status”.

Generally, they were a bit more physically active and less likely to be on HRT. This is one of those chicken or egg situations because there are two different ways of interpreting this: Are supplement takers healthier BECAUSE they take supplements; or do healthier people, CHOOSE to take supplements, the inference being that they were probably healthier to start with and probably don’t need them? Assuming the latter, which is a big assumption, the researchers then ‘ adjusted’ the results (details of exactly how they did this is not given in the paper) and got to the point where all the positive associations were no longer significant. Not stopping there, they further ‘adjusted’ the results and got to the point where the positive benefits became negatives, which is what went out in the press release. Comment: You have to be really biased to look at this data and conclude that supplements are a waste of time, and probably harmful.

You can only really reach that conclusion if you believe all the ‘adjustments’, based on a subjective judgement, are valid. The main question that the survey set out to answer was ‘do supplement takers have a higher or lower mortality risk?’ The answer to that question is that they have a lower risk, which generally reduces over time, with the exception of iron. One judge of whether the books have been rightly or wrongly cooked is common sense. For example, in the main analysis vitamin D, which is well established to reduce mortality, is shown to do just that. By the final analysis, the one that hit the headlines, the reverse is true. This is exceedingly unlikely and certainly makes me very suspicious of the validity of the ‘adjustments’. Anyway, bad news does sell newspapers better than good news so you can understand the media using these kind of scare headlines. I am, however, somewhat interested from a cautionary point of view in the strongest negatives, being iron, folic acid and possibly copper. Copper is an antagonist of zinc and

I’ve always made a point to supplement at least ten times more zinc than copper. I think that is a wise precaution. Also, post menstruation, women need less iron, not more. I recommend post-menopausal women not supplementing more than 10mg of iron unless you are proven to be anaemic. Folic acid, while good for younger women, could potentially be bad in higher doses for older women, especially if taken on its own and if you live in a country, like the US, where folic acid is added into flour. The reason for this is that, while folic acid stops healthy cells becoming pre-cancerous cells, there is evidence that it might be encourage pre-cancerous colo-rectal cells from growing into full blown cancer cells. I recommend supplementing no more than 200mcg unless you’ve been tested and have, for example, a raise homocysteine level. For more on this see my blog on folic acid and cancer So, what’s the take home message? This paper has far too many holes in the data massaging to be a basis for deciding whether or not to supplement. The line I read in the papers and the press release that

a) you can get all the nutrients you need from a well-balanced diet;

b) don’t take supplements unless there’s a strong medically-based cause for doing so because of the potential to cause harm is just propaganda. In my books and newsletters I continue to give medical science-based reasons to supplement, and ample evidence of non-existent harm. In thirty years in this field I have yet to see a serious adverse reaction, let alone a death, attributed to a vitamin supplement, and many people saved.

Top