It’s so ingrained into our notion of what constitutes healthy living in the UK and in other high-income countries, that it seems almost blasphemous to consider. But an increasing number of scientific trials are discovering that vitamin supplements may not be all they’re cracked up to be.

On a personal note, as a routine supplement swallower for many years, I was pretty surprised myself to discover (almost as soon as I started studying nutrition) that health organisations globally are agreed that vitamin supplements aren’t necessary for the vast majority of us. Aside from the vitamin D boost most of us in the northern hemisphere need during the winter months, unless you’re pregnant, malnourished, a newborn infant, elderly, following an exclusion diet (like veganism), or suffer from a chronic health condition like Crohn’s there’s simply no real need.

If you’re not going to make it to the end of this blog, I’ll save you some time, and say right now that nothing compares to the vast array of vitamins, minerals, fibre and naturally occurring phyto (plant) and zoo (guess) chemicals we can find in food. It was this realisation that spurred me on to set up The A to V as a resource for those looking for an alternative to the supplement life.

But with a growing number of hysterical articles in the media stating that supplements might kill you, what’s really going on?

Well, several trials have linked taking certain high-dose supplements with an increased risk of some chronic health conditions

A new study out this month in the Journal of clinical oncology looked at whether there was a link between B6, B9 (folate) and B12 supplementation, and incidences of lung cancer in a group of over 77,000 people followed over the course of a decade.

They found that B6 and B12 supplementation amongst the men of the group, was associated with a higher lung cancer risk that increased amongst those of the men who smoked.

These findings are in line with several other studies. In fact, they’re nothing new, and there’s a body of evidence here going back to the early 1990s that supports the notion of high-dosage supplements having unexpected and unintended effects.

With the antioxidant and anti-infectious benefits of vitamin A, vitamin E, and selenium well-known, the logic should follow that high doses of these micronutrients will reduce the effects of oxidative stress (and therefore the risk of cancer) in the body. But in fact several trials have shown the opposite.

One of the more infamous examples is the CARAT study of 1996 on a group of people at high risk for lung cancer, due to a history of smoking or asbestos exposure. The participants were given a beta-carotene supplement (which the body turns into vitamin A) with the expectation that this would reduce cancer rates in the group.  In fact the trial had to be halted early when those participants given the supplement were found to have a significantly higher risk both developing lung disease and of death.

Similar findings have been seen in large trials with vitamin E and selenium supplements (the SELECT trial is probably the most well-known). So what the hell is going on?

But can my multivitamin supplement really be that bad?

As with most things in life, it’s the dose that kills you – not the poison. In the study of B vitamin supplementation discussed above, the increased lung cancer risk was associated only with the highest levels of supplementation: more that 20mg/day of B6 and more than 55mcg/day of B12. 

These amounts are considerably higher than the RNI (recommended nutrient intake) in the UK, where adult women are advised to take just 1.2 mg per day of B6, and adult men 1.4 mg per day. It’s a similar story with B12, where 1.5 mcg per day is the recommended amount (some 3,566% less than the amount taken by the trial participants!).

There is also evidence to suggest that those micronutrients with antioxidant qualities work together in the body in an interconnected antioxidant network. Taking a high dose of just one of these micronutrients in isolation may well affect the entire system in ways we don’t yet know much about.

And certainly, with other trials the results have sometimes been inconclusive. Two large scale, randomised and controlled trials (the Physician’s Health Study I, and the Women’s Health Study) supplementing health professionals with beta-carotene found no benefit or harm from supplementation. A 2014 Cochrane review of 55 studies into selenium supplementation, found only inconsistent results as to selenium’s effect on cancer risk when used in controlled randomised trials.

Ok, but should I keep taking my multivitamin or not?

Where the recent B6 and B12 trial is concerned, we should always be wary of taking evidence based on cohort studies as an absolute truth. Cohort studies are where large groups of people are followed for long periods of time, and any incidences of disease are then mapped to any particular lifestyle traits shared by those unfortunate enough to become ill. While certainly providing extremely valuable evidence, this type of trial can’t conclusively prove causation, only identify possible likely associations.

It should also be pointed out that in the B6/B12 study no negative association was found in women, and no association was found when B-vitamins were consumed in the low doses contained in multivitamins. 

And this is probably the key point. In most of the trials showing negative effects, very high doses of single supplements are given. While this is certainly an important reminder for us all that vitamins and minerals are powerful compounds to be treated with respect, and not simply a health insurance policy that at worst leads to some seriously expensive urine, it’s unlikely that any properly regulated multi-vitamins are going to increase your risk of cancer.

Some final thoughts

While it’s an unnecessary expense for many of us in the West, we mustn’t forget that for many in middle and low-income countries supplements are often vital for health. Iron, iodine and vitamin A deficiencies are still the leading preventable cause of blindness, brain damage and anaemia globally. Supplementation here can quite literally save lives.

But for the vast majority of healthy adults with access to a wide variety of foods, you’re better off spending your pennies on fruit, veg, wholegrains and good quality protein instead of shiny looking supplements that promise the earth. Shifting our focus away from magic bullet superdoses, to the moderate vitamin and mineral amounts found naturally in food may be boring, but is certainly safer and cheaper.

References

https://www.nhs.uk/news/2011/05May/Documents/BtH_supplements.pdf

https://www.ncbi.nlm.nih.gov/pubmed/15572749

https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/#en40

https://www.ncbi.nlm.nih.gov/pubmed/16313697

https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/#h8

Price, C. (2016) The Vitamin Complex. London, Oneworld Publications, pp. 208-9.