Multivitamins controversy – more questions than answers

You could hardly have failed to notice the headlines this week; a new study claims to show that vitamins can kill you.

But before we find ourselves in the grip of widespread multivitamin phobia, it’s worth considering the context in which the story has appeared, as well as considering what the study actually said – versus what a sensationalist media would have you believe it said.

In America and in Europe the consumers’ freedom to continue to purchase the wide variety of nutritional supplements we currently enjoy is under threat. On both sides of the Atlantic powerful lobbyists are pushing to restrict what we can buy and to bring in complex and expensive registration and licensing procedures for vitamin and mineral supplements most of which have been on sale for decades and used safely by millions of people.

Should this happen, the manufacture of our vitamin supplements would likely fall solely to major pharmaceutical companies. Smaller companies who also make supplements would simply not have the funds available to meet the licensing requirements.

We are already seeing the beginning of something similar with herbal products in Europe, many of this were taken off the market in May 2011 under the auspices of the European Traditional Herbal Medicinal Herbal Products Directive (THMPD).

Had this context not been in place this study which, while interesting, is hardly the final word on the subject, would never have been given the space or attention it has received in the last two days.

So what did the study, published in the Archives of Internal Medicine, say?

The researchers’ aim was to study the effect of a range of nutritional supplements on premature death from a variety of causes. They concluded that while most dietary supplements have no effect either way on rates of early death, some appear to be “associated with an increased risk of death in older women.”

They go on to recommend:  “Based on existing evidence, we see little justification for the general and widespread use of dietary supplements. We recommend they be used with strong medically based cause, such as symptomatic nutrient deficiency disease.”

We should all be careful of taking pills of any kind without justification – and that includes the millions of ‘just in case’ and unproven conventional drugs which have become like so much hard candy in our daily lives. But the relatively weak associations found in this study really don’t justify the furore or the fear mongering, and in fact obscure some legitimate questions which arise from the data.

The researchers used information from a large ongoing women’s health study, the Iowa Women’s Health Study, to examine the association between vitamin and mineral supplements and mortality (death) rate among 38,772 older women. The average age in the study was 61.6 years.

Information about supplement use was self-reported, relied on the accurate recollections of the participants and was collected only three times over the 22 years of the study – in 1986, 1997 and 2004 – via questionnaires. Except for calcium and iron, there was no indication of the dosages taken.

Data based on recall is often unreliable. In addition, there was limited information on the health and nutritional status of the women involved. Furthermore, all the women in the study were white – so the results are not applicable across a multicultural society.

By the authors’ own admission the power of the study to prove anything other than an association between certain supplements and early mortality is relatively low.

Nevertheless, they report that in their study certain supplements increase the risk of dying early. The reported increased risk was around 5.9% for folic acid, 4.1% for vitamin B6, 3.9% for iron, 3.6% for magnesium, 3% for zinc, 2.4% for multivitamins and 1.8% for copper.

Not widely reported in the press was the fact that after adjustment for influential factors only multivitamins and copper showed any significant association with early death.

Also not reported in the press was the finding that calcium reduced the risk of death by 3.8%. Also not reported was that this effect diminished with increasingly high doses of calcium. The risks associated with iron were also dose dependent, rising as the estimated daily dose of iron rose.