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Vitamin supplements do not reduce the risk of cancer

Posted Apr 09 2009 7:17pm
Vitamin supplements do not reduce the risk of cancer

Vitamin supplements do not reduce the risk of cancer

The prospect of reducing your risk of cancer through popping a simple pill is certainly attractive. But the big question about vitamin supplements is this: do they actually prevent the disease?

The latest study to address this question has just come out today, in the Archives of Internal Medicine.

The study’s US authors looked at data from over 161,000 women, all of whom had been through the menopause and forty per cent of whom used multivitamins. They collected detailed information about these women and any multivitamins they used.

Over the next eight years, they compared women who took the pills and those who didn’t, and noted whether any of them went on to suffer from health problems, including cancer or heart disease.

The results were very clear. The multivitamins didn’t reduce the risk of developing breast, bowel, womb, lung, kidney, stomach, bladder or ovarian cancers.

They didn’t reduce the risk of heart attacks, blood clots or strokes.

They didn’t reduce the risk of dying at any given age.

If those facts sound quite negative, there is some good news hidden among them – the multivitamins didn’t increase the risk of these conditions either.

That seems like a strange cause for celebration, but it’s a valid one. When scientists first started putting vitamin supplements through their paces in clinical trials, one of the most unexpected results was that some high-dose supplements could actuallyincreasethe risk of some types of cancer..

More evidence

The conclusion that vitamin supplements aren’t helpful (and could even be harmful) has come through again and again in the majority of trials. Here are just a few examples:

  • Folate (vitamin B9) supplements could reduce the risk of developing bowel cancer, but there are concerns that they could also speed up the growth of existing cancerous cells.
  • Two clinicaltrials recently showed that supplements of selenium, vitamin E or vitamin C do not reduce the risk of prostate cancer. One of these, the SELECT trial, was stopped early because hints of potentially harmful effects were starting to show.
  • An analysis of 25 studies found that beta-carotene supplements do not protect against lung cancer. Another analysis of four clinical trials found that smokers who take these supplements are actually more likely to develop lung cancer.
  • An analysis of 14 trials concluded that supplements of beta-carotene, vitamins A, C, E, and selenium do not reduce the risk of oesophageal, stomach, bowel, pancreatic or liver cancer. They could even increase the risk of dying from these diseases.

Now, we’ve just picked a few studies that have come out in recent years. It’s not meant to be a thorough review of the evidence. Fortunately, other organisations have done just that.

Last year, the well-regarded Cochrane Collaboration reviewed 67 clinical trials on vitamin supplements. It concluded that supplements of vitamins A, C and E, beta-carotene and selenium do not improve your health. And the very best trials showed that beta-carotene, vitamin A and vitamin E supplements could possibly increase the risk of dying from various diseases.

Failed hope

The story of vitamin supplements and cancer is one of failed hopes. Back in the 1980s, there was a lot of excitement about these pills in the scientific community.

Researchers were beginning to find that people who ate foods rich in vitamins were less likely to develop certain types of cancer. Laboratory studies bolstered this optimism, by highlighting many different ways in which vitamins could counter the development of cancer. Concentrated versions of these vitamins in simple pill form should theoretically have provided an easy way of preventing cancer.

The sad fact is that this wave of hope has now well and truly broken. Vitamin supplements have failed to live up to this early promise. They have failed to demonstrate their worth in the majority of clinical trials. In some cases, they could even be harmful. That lesson has been a difficult pill to swallow, but it’s one that other organisations are paying heed to.

There are a couple of possible exceptions, for specific groups of people. Pregnant women, or those who are planning on becoming pregnant, are still advised to take folate supplements to reduce the risk of spina bifida.

And people who are likely to become vitamin D deficient may be advised to take vitamin D supplements. However, even for vitamin D, it is premature to advise that the wider population should start taking supplements.
The bottom line is that the best source of vitamins is the old-school, low-tech one – a healthy, balanced diet with a wide range of fruits and vegetables.

The benefits offered by these diets were the basis for the initial wave of optimism surrounding supplements. We now know that these pills, popular though they are, cannot substitute for vitamin-rich foods. They’re simply nowhere near as good for you. Some of them could even cause you harm.

Ed



Reference:

Marian L. Neuhouser, Sylvia Wassertheil-Smoller, Cynthia Thomson, Aaron Aragaki, Garnet L. Anderson, JoAnn E. Manson, Ruth E. Patterson, Thomas E. Rohan, Linda van Horn, James M. Shikany, Asha Thomas, Andrea LaCroix, Ross L. Prentice. (2009). Multivitamin Use and Risk of Cancer and Cardiovascular Disease in the Women’s Health Initiative Cohorts. Archives of Internal Medicine 169 (3), 294-304
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