Press releases

Warning on high-strength vitamin supplements

19 October 2009

A cancer expert has warned that people who take high-dose vitamin and mineral supplements might do themselves more harm than good.

Professor Martin Wiseman, Medical and Scientific Adviser for World Cancer Research Fund (WCRF), has said it is difficult to make confident predictions on what impact supplements – and particularly high-dose ones - have on cancer risk.

Lower dose supplements are recommended or can be a valuable safety net in some situations. However, in some cases high-dose supplements can have a harmful effect and this is why WCRF recommends that rather than taking dietary supplements for cancer prevention, people should aim to get the benefits from eating a healthy diet.

But despite this advice, according to statistics from the Food Standards Agency 31 per cent of people say they take a supplement and about 15 per cent say they have taken a high-dose supplement in the last year.

Professor Wiseman said: “Many people think they can reduce their cancer risk by taking supplements, but the evidence does not support this.

“Just because a dietary pattern that provides a relatively high level of a particular nutrient might protect against cancer, it does not mean that taking it in tablet form will have the same effect. In fact, at high doses the effect of these micronutrients is unpredictable and can be harmful to health.

"Although there are some studies that have shown a reduction in cancer risk from high-dose supplements, others have not, and these supplements have normally only been tested on a select group of people. This means we simply do not know enough about what the effect will be for the general population to confidently predict the balance of risks and benefits. Some people may be doing themselves more harm than good.

“There are also studies that show high doses of some supplements can increase risk of some cancers. For example, there is convincing evidence that taking beta-carotene supplements actually increases the risk of lung cancer in current smokers.

“Even multi-vitamin supplements with a wide range of nutrients will not contain all the beneficial substances found in foods, such as fibre. There is little evidence on whether these low-dose dietary supplements affect the chances of getting cancer, even for people whose diets are otherwise less than ideal, so more research is needed. Until then, the best advice is to have a healthy, plant-based diet with lots of fruits and vegetables, rather than relying on supplements.

"The evidence about the difficulty in predicting the effect of high-dose supplements is getting stronger all the time.

"For example, in 2007 we concluded that taking selenium supplements probably reduces risk of prostate cancer. But a recent study unexpectedly found no evidence that it reduces risk, so my personal interpretation would be that the jury is still out on this.

"Equally, the findings of another American study have raised the concern that high intakes of multi-vitamins might increase risk of advanced prostate cancer, although more research would be needed before we could be confident this is really the case.”

For ideas for recipes that can form part of the kind of diet that can reduce risk of cancer, visit www.wcrf-uk.org

ENDS

Notes to editors:

• Much of the research showing high-dose dietary supplements influencing cancer risk was conducted among people who were already at high risk for cancer. That means the results from these studies may or may not extend to the rest of the population.
• Some groups of people may benefit from taking supplements. These are the most common situations when taking a supplement would be beneficial:
• All women intending to conceive a child should take a 400mcg folic acid supplement before conception and up to the 12th week of pregnancy.
• Pregnant women and nursing mothers should take a vitamin D supplement and possibly an iron supplement if their iron level is low.
• Children between six months and five years could benefit from taking drops containing vitamins A, C and D.
• Children with a good appetite who eat a wide variety of foods may not need them.
• Frail older people who have low calorie needs may benefit from a low-dose multivitamin supplement. Older people should consider taking a vitamin D supplement, as should: people of Asian origin; people who rarely go outdoors; people who cover up all their skin when outdoors; those who don’t eat meat or oily fish.
• For more advice on any of these situations, it’s best to contact your GP.

back to top

About WCRF

World Cancer Research Fund (WCRF) raises awareness that cancer is largely preventable and helps people make choices to reduce their chances of developing the disease.

This includes research into how cancer risk is related to diet, physical activity, and weight management, and education programmes that highlight the fact that about a third of cancers could be prevented through changes to lifestyle. For more information on the charity’s work, visit www.wcrf-uk.org

The WCRF report, called Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective, was launched in November 2007 and is the most comprehensive report ever published on the link between cancer and lifestyle. For more information, visit www.dietandcancerreport.org