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Vitamins

Headlines claiming that “vitamins lower cancer risk” don’t truly reflect trial results

The media’s search for a ‘magic pill’ to reduce cancer risk continues. Yesterday saw several stories about multivitamins “lowering the risk of cancer”. Some of the headlines would have you believe the magic pill has been found – but unfortunately it’s not that simple.

The headlines were based on the results of a study published in the Journal of the American Medical Association, which looked at the effects of taking multivitamins on cancer in middle-aged or older men.

Over 11 years, about 15,000 male health professionals took either a general multivitamin, or either vitamin E, vitamin C, beta carotene (a precursor of vitamin A) or a dummy pill (placebo). This was a ‘blind’ trial, so neither the researchers nor the men on the study knew which pill they were taking. The study included men with a history of cancer as well as healthy individuals.

Daily multivitamin use was shown to slightly reduce the overall risk of developing cancer – by 8 per cent. To put that in perspective, about 18 cancers per 1,000 people per year were diagnosed in the placebo group, compared with  17 cancers per 1,000 people per year in the multivitamin group.

But we don’t recommend you rush out to your local vitamin emporium based on this research. Let’s take a look at why…

Study limitations

There are many things about this study that are good. It’s a randomised, blinded, placebo-controlled trial – the gold standard for scientific studies. It’s also a large-scale, long-term study, and one of the first to look at the effect of multivitamins rather than single supplements.

But we think that some of the limitations of this research mean yesterday’s headlines extolling the benefits of vitamins might have been too optimistic:

  • When the authors looked at the impact of multivitamin use on developing certain specific types of cancer, including prostate, bowel and lung cancers, they saw no reduction in risk. And taking multivitamins did not reduce the risk of dying from cancer.
  • Even the apparent reduced risk for all cancers is debatable. If you look at the confidence interval – the range of values between which there’s a 95 per cent chance the true answer lies – you hit a problem. The top of the range for ‘all cancers combined’ was so close to ‘no effect’ that if they had rounded this figure in the same way as the others in the study, the results wouldn’t have been statistically significant (i.e. was small enough to just be random variation) and no link between multivitamin use and cancer could be claimed.
  • We can’t be sure that the study group stuck to the tablet routine they’d been given. In the first year, men were sent packs containing either a multivitamin or placebo every 6 months, then annually after that. Whether they remembered to take the pills was only verified by annual questionnaires. So the research relied on people taking a pill every day for a number of years, accurately remembering what they took – and being honest about how well they stuck to it.
  • The groups of people that took different types of vitamins took them for different lengths of time. So while beta carotene was taken only for around 6 years, vitamin E and C were taken for about 8 years, and only the multivitamin was given over almost 12 years. This makes it harder to compare different groups if several different things are changing at the same time. It is also unclear why the researchers didn’t report the results on how the single vitamin tablets affected cancer risk.

The NHS Choices website has a more in-depth analysis of the strengths and weaknesses of the study, and is well worth reading.

Other studies paint a different picture

There’s already a wealth of evidence on the impact of vitamins on cancer risk. In 2008, an organisation called the Cochrane Collaboration reviewed the results of 67 clinical trials of vitamin supplements. It found that far from prolonging a person’s life, vitamins either have no effect or could even be harmful.

We wrote about this review and other studies on vitamin supplements a few years ago, and broadly speaking, the points we raised then still stand.

Conflicts of interest

As with any research, it’s also worth reflecting on who funded the study. This work was funded by the US National Institutes of Health and the BASF Corporation – a chemical company that produces dietary supplements among other products – although the funders had no role in how the study was designed, carried out or interpreted.

It is not unusual for research funding to come from several sources, and sometimes funders include those who could be deemed to have a ‘vested interest’ in the results. A good example is pharmaceutical companies running clinical trials of their own drugs – obviously they have a vested interest, but they also have a crucial role in paying the huge sums of money required to run such trials so that patients can benefit from drugs found to be effective.

This is why good quality journals such as JAMA request that such conflict of interests are declared in publications. Alongside crucial information about the quality of a study, knowing who the funders of research are can help you weigh up the conclusions.

Take-home message

Our overall message is simple – vitamin and mineral supplements are no substitute for a healthy diet and neither do they have the same benefits as getting naturally-occurring nutrients in your food. And this latest study certainly does not warrant some of the more over-zealous claims like “multivitamins dramatically slash the risk of men developing cancer”.

It’s thought that the vitamins and other nutrients in fruit and vegetables interact with other chemicals to produce positive effects – the same cannot be said of supplements.The best way to get a full range of vitamins and minerals is to eat a healthy, balanced diet with a wide variety of fruit and vegetables – in which case there shouldn’t be a need for supplements.

However, some people may be advised by their doctor to take dietary supplements at certain times in their lives. For example, doctors may advise women who are planning to have a baby to take a daily folic acid (vitamin B9) supplement. And some people might need vitamin D supplements – for example people who are elderly or housebound, who wear full body coverings or who have dark skin. If you’re concerned about your vitamin levels, you should talk to your doctor.

Helga Groll, Health Information Officer

Reference

  • Gaziano, J.M. Multivitamins in the Prevention of Cancer in MenThe Physicians’ Health Study II Randomized Controlled TrialMultivitamins in the Prevention of Cancer in Men, JAMA: The Journal of the American Medical Association, DOI: 10.1001/jama.2012.14641

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Comments

Maureen. October 20, 2012

I have worked with cancer patients in a complementary situation, and have witnessed what they have been through mentally and emotionally, I am no expert but In my mind they may be lacking in vitamins we do not get enough through the food chain…maybe we need to top ourselves up.