Vitamin D and Breast Cancer Prevention | Is There a Connection?

by Natalie

Over the past few years you may have noticed a lot of information in the media about vitamin D and cancer.

The scientific community has been studying vitamin D and its role in cancer prevention extensively over the past two decades. Some research studies have found a connection between vitamin D and cancer prevention, especially cancers of colon, prostate and breast.

This information may have got you wondering about vitamin D and asking questions like: what is vitamin D? How much vitamin D do I need? How do I know if I am getting enough? Should I be taking a supplement?

This article will address all of these questions and more. I will also delve deeper into the question about vitamin D and breast cancer prevention.

What is Vitamin D?

Vitamin D is known as the “sunshine vitamin” because our bodies can create it when our skin has contact with UV rays from the sun. Vitamin D is actually considered to be a hormone because it acts like one in the body.  Vitamin D is fat-soluble, meaning  it needs some dietary fat to be absorbed.

Role of Vitamin D

Vitamin D helps to keep our bones healthy and strong. It also helps us to absorb calcium. Research continues to be conducted to determine if it has any other health benefits.

Sources of Vitamin D

There are 3 sources of vitamin D:

  • Sun: our bodies make vitamin D when our skin contacts UV rays.
  • Food: vitamin D is found naturally in a few foods, while other foods have been fortified with it.
  • Supplements: the supplements come in two forms, Vitamin D2 and D3. There is somewhat of a debate over which form is better utilized. Firm conclusions about their differences cannot be drawn at this time. Currently both forms are considered equivalent but high doses of D2 are less potent (1).

Food Sources of Vitamin D

Vitamin D exists naturally in a few animal products, especially in fatty fish. Some mushrooms also provide vitamin D in varying amounts.  Many foods have been fortified with vitamin D, these include: milk, cereals, some yogurts and some orange juices. Below I have listed foods high in vitamin D (2).

  • 1 T cod liver oil = 1360 IU
  • 3 oz cooked rainbow trout = 645 IU
  • 3 oz cooked Sockeye salmon = 447 IU
  • 3 oz canned tuna = 229 IU
  • 3 oz cooked halibut = 196 IU
  • 8 oz fortified cow’s milk = 120 IU
  • 1 oz canned sardines = 56 IU
  • 1 C cooked shitake mushrooms = 41 IU
  • 1 egg yolk = 36 IU
  • 1 C cooked white button mushrooms = 12 IU

Vitamin D from the Sun

It is difficult to determine how much time in the sun in takes to form adequate vitamin D because there are many factors that affect the sun’s efficiency. However, researchers have considered 5-30 minutes of sun exposure between the times of 10am-3pm, without sunscreen, two times per week, to be adequate for our bodies to form enough vitamin D (1).

Factors affecting the sun’s efficiency (1):

  • Clouds. Complete cloud cover reduces UV energy by 50%
  • Glass windows. The UV rays needed to form vitamin D do not penetrate glass. Therefore, you cannot sit by a sunny window to produce vitamin D.
  • Sunscreen. SPF greater or equal to 8 will block vitamin D producing rays.
  • Melanin. The darker your skin, the more melanin you have. Higher melanin reduces your ability to produce vitamin D from the sun.
  • Age. Skin has a reduced ability to produce vitamin D with age.

How Much Do We Need?

The Food and Nutrition Board at the Institute of Medicine (IOM) has established a recommended dietary allowance (RDA) for Vitamin D. This recommendation was established only to determine the level of vitamin D to maintain bone health and normal calcium metabolism, not for any other condition or disease. The RDA was reviewed and updated in November of 2010.  Also, it is important to know that these new reference values assume a person has minimal sun exposure.

Use the link above to see the RDA for all age groups. The RDA for adult women is 600 International Units (IU) a day. The Upper Level Intake (UL) is 4000 IU for adult women. UL means the highest daily intake amount of a nutrient that is likely to pose no risk of adverse health effects.

Can I Get My Vitamin D levels Checked?

Vitamin D status is determined by checking the level of 25-hydroxyvitamin D (25OHD) in your serum (blood). However, according to the IOM, serum levels of 25OHD have not been validated (3). Meaning, there is no scientific consensus on what these levels should be.  Therefore, different doctors may use different standards to assess your vitamin D status.

Based on a review of the data available, a committee of the IOM developed cut-points for serum vitamin D levels (3). Here is what they came up with:

  • Deficient at serum levels less than 12 ng/mL
  • Inadequate at serum levels of 12-20 ng/mL
  • Sufficient at serum levels of 20ng/mL: a benefit for most people is associated with this level
  • Levels greater than 50 ng/mL are associated with potential adverse side effects

Vitamin D and Breast Cancer Prevention | Is there a connection?

Over the past decade, more research has become available showing that vitamin D may have a protective effect against breast cancer. However, the evidence has been inconsistent. The IOM concluded in their summary report that a relationship between cancer prevention and vitamin D cannot be adequately demonstrated at this time (3). They did, however, call the research related to cancer and vitamin D of “potential interest”.

I performed a review of nine recent research articles published on the topic of vitamin D and breast cancer.  Several of the articles concluded that adequate vitamin D levels may lower a women’s risk for breast cancer (4,5,6,7,8).  However, more is not always better.  Other articles I read cautioned against excess amounts of vitamin D saying that higher serum levels of vitamin D may have negative effects for women with breast cancer or that high vitamin D levels may result in an increased risk for certain cancers (6,9).  Pretty much all of the studies concluded that more research needs to be done to determine what level of vitamin D in the blood will produce positive results.

Based on the research reviewed, there appears to be a relationship between vitamin D and breast cancer prevention.  The amount of vitamin D to produce this effect is yet to be determined.  With time we should expect to see more research done on the topic, which hopefully, will make things more clear.  Until then, I believe we should remain conservative with vitamin D supplementation.

Vitamin D Supplements

After reading the section above, you may be wondering if you need to take a supplement. The answer to this question really depends on the individual. Our primary source of vitamin D is the sun, but as stated previously, many things factor UV efficiency. So if you are an individual who stays indoors all the time, are of older age, have darker skin, yes you may benefit from a supplement.  It really all depends on your particular lifestyle.

If you think you could be at risk for a vitamin D deficiency, I think the best thing to do would be to get tested.  Ask your doctor at your next visit if you can get tested.

I take a vitamin D supplement over the winter months (Dec-March). Here in the Midwest, the days are short and cold during the winter, and I rarely get outside! I eat sockeye salmon occasionally but not enough to provide the daily requirement. The amount of vitamin D I take is 1000 IU in the form of vitamin D3.  In my own opinion, I would be hesitant to take any vitamin D supplement greater than this amount without having my vitamin D levels checked.


From my review of current research, it appears that vitamin D may have a protective effect against breast cancer. However, more research needs to be done to determine the amount we should take and what optimal blood levels should be. Also, more is not better! A few studies indicated that higher amounts of vitamin D may actually increase risk for certain cancers.  Our primary source of vitamin D is the sun, but many things affect UV efficiency.  If you think you may be at risk for a deficiency,  you should ask your doctor if he/she can order the test.

Pheww! That was a lot of information about vitamin D!



photo by: davedehetre


(1) National Institutes of Health, Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D.

(2) U.S Department of Agriculture, Agriculture Research Service. USDA National Nutrient Database for Standard Reference, Release 23, 2011.

(3) Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.

(4) Garland CF, Gorham ED, et al. Vitamin D and prevention of breast cancer: Pooled analysis. J Steroid Biochem Mol Biol. 2007;103:708-711.

(5) Robien K, Cutler GJ, et al. Vitamin D intake and breast cancer risk in postmenopausal women: The Iowa Women’s Health Study. Cancer Causes Control. 2007;18:775-782.

(6) Goodwin PJ, Ennis M, et al. Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer. J Clin Oncol. 2009;27:3757-3763.

(7) Bertone-Johnson ER. Vitamin D and breast cancer. Ann Epidemiol. 2009;19:462-467.

(8) Garland CF, Gorham ED, et al. Vitamin D for cancer prevention: Global perspective. Ann Epidemiol. 2009;19:468-83.

(9) Toner CD, Davis CD, Milner JA. The vitamin D and cancer conundrum: Aiming at a moving target. J American Dietetic Assoc. 2010;110:1492-1500.



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