Confusion reigns over multi-vitamins and breast cancer

Consider these two headlines published in the last couple of days:

multivitamins1New Zealand Herald:  Major research finds link between multi-vitamin pills and breast cancer

BusinessWeek: Supplements might reduce breast cancer risk

Both are top search results on Google News, but don’t they seem to contradict each other? Let us look a little more closely at the stories. Here’s the intro for the Herald story:

Women who regularly take multi-vitamin pills face a much higher risk of breast cancer, a study has found.

And here’s BusinessWeek‘s intro:

Women who take multivitamin tablets along with calcium supplements seem to have a reduced risk of developing breast cancer, new research suggests.

Okay, so they definitely seem to contradict each other – or does the “along with calcium supplements” mentioned in the BusinessWeek story make all the difference: ie is taking calcium supplements along with  multivitamin tablets rather than just multivitamin tablets alone really the difference between a woman increasing or decreasing the risk of her developing breast cancer?

The answer is no. BusinessWeek continues:

Taking a multivitamin tablet reduced the risk of tumors by about 30 percent, while calcium supplements reduced the risk by 40 percent, the study authors noted.

So calcium is a breast cancer fighter according to this research, but so too are multivitamins, which the Herald suggests can increase the risk of developing breast cancer. The study referred to by BusinessWeek, Associated Press and others is from researchers at Ponce School of Medicine in Ponce, Puerto Rico. It involved the authors comparing “vitamin and calcium intakes of 268 women with breast cancer and 457 women without breast cancer, all in Puerto Rico”. The research was presented at the American Association for Cancer Research annual conference in Washington, D.C. over the weekend.

The Herald report and numerous others refer to a different piece of research conducted by Sweden’s Karolinska Institute and published in the American Journal of Clinical Nutrition. This 10-year study involved more than 35,000 women, and researchers discovered those who regularly took a multi-vitamin pill “increased the risk of developing a tumour by 19 per cent”.

Lack of context

What appears to have happened here is two pieces of research emerged over the same weekend with contradictory conclusions. One is a very large study, the other relatively small. But I haven’t found a story on Google News that refers to both stories, weighing up the results and putting each in context alongside the rival study. As a result, anyone browsing the web is likely to see directly contradictory stories examining the same issue – whether multivitamins impact the risk of a woman developing breast cancer.

Just posted, by the ABC News in Australia, this piece which quotes head of surgical oncology at Newcastle’s Calvary Mater Hospital, Professor John Forbes”

He says the results of the Swedish study are barely statistically significant and do not indicate what the outcome might be for women taking fewer vitamin tablets.


  1. Jim McVeagh

    Firstly, neither study establishes the original vitamin state of the participant. It is quite likely, for instance that the Puerto Rican participants were mostly both vitamin and calcium deficient.
    Secondly, the Swedish study is quite flawed. The vitamin use has been determined by questionnaire and the marked “yes” for supplementation if the subject admits to taking one a week. No attempt has been made to determine type of multivitamin taken or quality of multivitamin.
    There are a limited number of multivitamin formulations available in Sweden. All contain Vitamin A (which is fairly toxic) and 300-400mcg of folate. Women who took the multivitamin were far more likely to take additional folate making their total intake very high. High levels of folate have been associated with increased cancer risks in some studies (this caused the withdrawal of folate supplementation of bread last year)
    In addition, the study found that multivitamin users were more likely to be nulliparous, use oral contraceptives and postmenopausal hormones, all of which are strongly associated with breast cancer. Though they have corrected for this, their resultant confidence intervals are so wide as to render this study virtually meaningless.
    There are multiple US cohort studies that find either no association or a negative association between breast cancer and multivitamins. It is therefore highly likely that some other factor that the study has not corrected for is causing this correlation, rather than the simple use of multivitamins.

  2. David Winter

    Hi Peter,

    I just wrote post tangential to this one, which will no dobt appear at sciblogs soon.

    As far as your pill popping woman, I think the guardian has the best advice:

    If you are a woman and regularly take a multivitamin, you may be concerned by these findings. However, we don’t yet know whether multivitamins actually increase the risk of breast cancer. We need more studies.

    However, we also don’t know whether these supplements have benefits for most healthy people. If you eat a well-balanced diet, you might reconsider whether you need to take a multivitamin.

  3. Fabiana Kubke

    Well, a paper is a bit of evidence, never the whole story. I am not sure the paper is being downplayed, it seems to me that it is the reports on the paper. A non-peer reviewed paper should not even be considered evidence (or reported as such). At most one can say ‘a presentation by such and such shows they are working towards getting whatever answer/goal’. But presenting the preliminary findings as validated result is just like to tethering a goat: just downright wrong! 🙂

  4. Peter Griffin

    I know, which makes it all the more confusing! The peer-reviewed, large-scale study is the one doctors and scientists are downplaying. What’s a regular multi-vitamin pill popping woman supposed to do?

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