Experts allay fears over multivitamins and breast cancer risk

By Stephen Daniells

- Last updated on GMT

Related tags Breast cancer Breast cancer risk Nutrition

A study linking multivitamin use to an increased risk of breast cancer does not prove the supplements are causing cancer, and shouldn’t stop multivitamin use, say experts.

Swedish researchers reported that multivitamin use may increase the risk of breast cancer by 19 per cent, according to data from a 9.5 year study involving over 35,000 women aged between 49 and 83.

Writing in the American Journal of Clinical Nutrition​, the Stockholm-based researchers said the apparent link is a “concern and merits further investigation”​.

Complex relationships

Despite spawning a range of headlines, including “Could multivitamins raise breast cancer risk?”​ from Reuters, the American Institute for Cancer Research (AICR) said that the study does not provide “a reason to throw out your one-a-day vitamin”​, and that the role of supplements in cancer risk is anything but clear-cut.

“Although researchers like to study the effect of promising nutrients in isolation, it’s unclear whether a given vitamin or mineral behaves the same way when it’s consumed as a supplement as when it’s consumed in a whole food,”​ said the AICR.

“Because of such complexities and lingering questions, The American Institute for Cancer Research recommends looking to the whole diet to get the vitamins, minerals and phytochemicals that potentially help protect against cancer,”​ it added.

Multivitamin use

According to a National Institutes of Health (NIH) State-of-the-Science Panel, half of the American population routinely use dietary supplements, with their annual spend estimated at over $20 billion.

Recent results of the National Health and Nutrition Examination Survey showed that 35 per cent of the US adult population regularly consumes one or more types of multivitamin product (Am. J. Epidemiol​., 2004, Vol. 160, Pages 339-349).

A recent study by US researchers reported that long-term regular consumption of a multivitamin may reduce the risk of dying from heart disease by 16 per cent (Am. J. Epidemiol​, Vol. 170, pp. 472-483), while another study reported that multivitamins users may have a younger ‘biological’ age (Am. J. Clin. Nutr​. Vol. 89, pp. 1857-1863).

There is also some data supporting some anti-cancer activity, with a US National Cancer Institute-sponsored study reporting in February that multivitamin supplements that are rich in phytochemicals, such as vitamin C, carotenoids, lutein, folic acid, and vitamins A and K may reduce the risk of lung cancer in smokers. Other studies have reported no link between multivitamins and cancer risk.

No causality

The study was slammed by the Health Food Manufacturers' Association (HFMA), a UK-based trade organisation, as “fundamentally flawed”​. Graham Keen, Executive Director of the HFMA said: “The study was not designed to establish cause and effect, and the researchers themselves agree that the findings do not prove that vitamins are to blame for incidence of breast cancer.

“Vitamins and minerals are not just useful for good health and wellbeing, they’re essential. In an ideal world, our diet would provide us with all the vitamins and minerals that our body needs for good health. But evidence from the FSA’s latest National Diet and Nutrition Survey shows that a significant proportion of the UK population simply doesn’t achieve nutritional sufficiency through diet alone,” ​said Keen.

“The best solution for most people is to eat as healthy a diet as possible, combined with other health-related lifestyle changes. For those looking to safeguard their nutritional intake, daily multivitamin supplements provide essential nutritional insurance for millions of consumers,” ​he added.

Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.2009.28837
“Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women”
Authors: S.C. Larsson, A. Akesson, L. Bergkvist, A. Wolk

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