Vitamin D: Does It Prevent Breast Cancer?

PJ Hamel Health Guide
  • Vitamin D, the “sunshine vitamin,” has been appearing all over the news lately. It’s supposed to improve your brain, cut your risk of cardiac disease and stroke, and ward off fibromyalgia.  It may even lessen your chance for issues as wide-ranging as multiple sclerosis and depression.

    And what about breast cancer? Will popping a 1000IU vitamin D supplement every day keep you from being that “1 in 8”?


    The Women’s Health Initiative is a long-term study tracking a range of health issues and involving 36,200 American women. The WHI is the study that pulled the plug on the popularity of Prempro as a menopause treatment, when it showed that long-term use of that hormone replacement drug increased the risk of breast cancer.

    Add This Infographic to Your Website or Blog With This Code:

    Last November, the WHI released results of a trial showing the connection between vitamin D and breast cancer prevention. The short story is that, while women who took a 400IU vitamin D supplement daily were less likely to get breast cancer, the difference was statistically insignificant.

    But the longer story is that the test wasn’t strictly controlled; all of the women in the study were free to take vitamin D supplements if they wished. And 400IU is increasingly thought to be way too low a dosage to provide the maximum benefits this vitamin seems to offer.

    Another study released this month, this one detailed in the Archives of Internal Medicine, concludes that vitamin D levels have “dramatically decreased” among Americans over the past 20 years. And that 75% of all Americans now have vitamin D levels below what’s traditionally been recommended.

    So, as a population our vitamin D levels are dropping, just as research is beginning to show newly discovered, wide-ranging benefits associated with it. Will our national vitamin D deficiency eventually lead to more health problems—including an increase in breast cancer?

    Dr. Michael Holick thinks so. Holick, director of the Vitamin D Laboratory at Boston University, has written that if women maintained a high level of vitamin D, their risk for colorectal cancer would be reduced by up to 253%; heart disease and stroke, more than 100%; and breast cancer, a reduction of up to 50%.

    And what qualifies as a “high level?” Current recommendations are for 400IU a day for women over 50 (200IU for women under 50). But it’s expected that new guidelines, with a dramatic increase in the recommended level, will be issued soon—perhaps as soon as next year.

    Anticipating that, many health-care providers are now recommending adults take vitamin D supplements totaling 800-1000IU per day, with a recommended top level from all sources (supplements, sunlight, and food) of about 1700 IU a day.

    Why wait for those new guidelines? Start increasing your vitamin D now. Full sun on your arms and/or legs two or three times a week, for 10 or 15 minutes each time, is a great source of vitamin D—and it’s free. But it’s also tough to get. If you live in the northern two-thirds of the U.S., the sun is too weak from October to April to provide any benefit. The smoke and smog of cities also screens sunlight; as does any sunscreen over SPF 8. And if you’re Hispanic or black, your darker skin is cutting back on your vitamin D absorption from sunlight.

  • Unlike calcium, which is easily accessible via diet (dairy products, calcium-fortified juice and cereal), diet alone won’t provide you with enough vitamin D. Unless you want to take a tablespoon of cod liver oil every day, or eat a pound of oily fish, you’re not going to consume enough vitamin D.

    Add This Infographic to Your Website or Blog With This Code:

    So supplements are the answer. First, check how much vitamin D is in your daily multivitamin. Then figure out how much you need to add to get up above 1000IU—perhaps up to that 1700IU level many health-care providers are now recommending. Vitamin D tablets, in 400IU and 1000IU, are fairly inexpensive. Look for vitamin D3 (or vitamin D labeled “as cholecalciferol”); it’s more easily absorbed than vitamin D2.

    If you’re part of the 75% of Americans suffering from low vitamin D levels, this can only help. And if you’re a woman worried about breast cancer, you might just be lowering your risk for that disease—even if the data isn’t in quite yet.

Published On: April 23, 2009