Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Breast Cancer Health Center

Font Size

Multivitamins Linked to Breast Cancer Risk

Study Shows Higher Risk of Breast Cancer Among Women Who Report Taking Multivitamins
WebMD Health News
Reviewed by Laura J. Martin, MD

April 1, 2010 -- The message is hammered home every time we turn on the TV: Taking a daily multivitamin can help improve our overall health and well-being and may even protect against diseases like cancer. But now a new study suggests that this seemingly healthy habit may actually increase the risk of breast cancer.

The new findings appear online in the American Journal of Clinical Nutrition.

In the study of more than 35,000 Swedish women aged 49 to 83, 25.5% said they took multivitamins. None of the women had cancer when the study began. During about 10 years of follow-up, 974 women were diagnosed with breast cancer, and 293 of these diagnoses occurred among the 9,017 women who reported using multivitamins.

Overall, women who reported taking multivitamins were 19% more likely to develop breast cancer than their counterparts who said they did not take daily multivitamins. These findings held after the researchers adjusted for other risk factors including family history, advancing age, body mass index, smoking status, and alcohol use.

"The potential health benefits or adverse effects associated with multivitamin use are of great public health importance [and] the observed association is of concern and merits further investigation," conclude the researchers, who were led by Susanna C. Larsson, PhD, of the division of nutritional epidemiology at the National Institute of Environmental Medicine at the Karolinska Institute in Stockholm, Sweden.

Possible Reasons for Breast Cancer Risk

So how could something that is supposed to be so good for you actually cause breast cancer?

The study could not establish cause and effect, but it did show an association of multivitamin use and increased risk of breast cancer.

There may be some biologically plausible reasons that multivitamins can increase breast cancer risk, the researchers say. For one, folic acid, an ingredient in many multivitamins, may increase breast density, which could potentially stimulate the development of cancer.

Some studies have also linked iron and zinc to increased cancer risk, though there have also been other studies that showed no association between these ingredients and cancer risk, the researchers say.

Today on WebMD

Breast Cancer Overview
From self-exams and biopsies to reconstruction, we’ve got you covered.
Dealing with breast cancer
Get answers to your questions.
woman having mammogram
Experts don’t agree on all fronts, but you can be your own advocate.
woman undergoing breast cancer test
Many women worry. But the truth? Most abnormalities aren’t breast cancer.
Breast Cancer Treatments Improving
Resolved To Quit Smoking
Woman getting mammogram
Screening Tests for Women
ovarian cancer overview slideshow
serious woman
what is your cancer risk
10 Ways to Revitalize Slideshow