Vitamin D and Breast Cancer Risk. What's the Connection?

Vitamin D Receptors (VDR) are located in every major organ and in tissues throughout your body. Vitamin D is more than a vitamin. It interacts with over 3,000 genes throughout the body so it’s crucial to get enough and know your levels.

The connection between vitamin D deficiency and cancer was first made in 1980 when two doctors learned the incidence of colon cancer was nearly three times higher in New York than in New Mexico. The doctors determined lack of sun exposure played a critical role (1). When the ultraviolet portion of sunlight hits your skin, this stimulates the body to produce vitamin D. This lack of sun exposure results in a lack of vitamin D in our body.

Consider the relationship between vitamin D and breast cancer. According to the Vitamin D Council, there is strong evidence vitamin D plays a beneficial role in lowering breast cancer risk. Whether vitamin D is obtained from sun exposure, food, or supplements, vitamin D must undergo chemical reactions to become calcitriol, which may provide the numerous benefits against cancer (2). Calcitriol encourages cells to either adapt to their organ or go through normal, programmed cell death (3). Calcitriol also limits blood supply to the tumor and reduces the spread of cancer (4). To simplify, vitamin D may play a role in controlling normal breast cell growth and may be able to stop breast cancer cells from growing.    

Vitamin D and You

Sun vs. Supplements

The primary way Mother Nature intended for you to incorporate vitamin D is through sunlight. Many studies have found vitamin D produced from solar ultraviolet-B (UVB) is associated with a reduced risk of breast cancer (5, 6). Isn’t it interesting Norwegian women diagnosed with breast cancer in the summer had higher survival rates than those diagnosed in winter? People typically have higher vitamin D levels in summer than winter, which may explain the findings. Also, African American women diagnosed with breast cancer generally have lower survival rates than white Americans, and lower vitamin D levels may be a contributing factor, attributed to lower production rates of vitamin D from solar UVB because of darker skin (7, 8).

Winter and Summer Months

Humans make 90 percent of their vitamin D naturally through sun exposure to the skin, but this is skin without sunscreen. In the summer months, many people slather on sunscreen and wear hats, long-sleeved rash guards, and anything else to "hide" from the sun's harmful rays. My point is, don't assume you are getting enough vitamin D from the sun during the summer months. 

In the winter months, depending on where you live and your lifestyle, sunlight can be difficult to come by. Even if you do spend time outdoors during the winter, the further north you live, the fewer the UVB rays that reach the earth’s surface. For northern climate countries, the sun's rays are too weak 4-6 months of the year to make any vitamin D naturally.

Vitamin D supplementation is an effective secondary alternative to sun exposure, provided adequate doses are taken. Vitamin D can also be obtained through your diet, but very few foods naturally contain vitamin D. Some foods containing vitamin D include vitamin D-fortified milk, yogurt, and orange juice, salmon, tuna fish, cod liver oil, and egg yolks. 

What are "Optimal" Vitamin D Levels? 

An expert group of 48 of the world’s leading vitamin D doctors, researchers and scientists have analyzed this question and came to a consensus to recommend that everyone, all ages, achieve a vitamin D blood level or 25(OH)D level of between 100-150 nmol/L (40-60 ng/ml USA). Here is a chart which shows you the diseases prevented at this level.

Studies found the risk of breast cancer falls as vitamin D blood levels rise to over 40 ng/mL (9, 10).

In one study, women with vitamin D blood levels above 150 nmol/L had an 82% lower incidence of breast cancer compared to women with levels

Are You Getting the Right Dose?

Vitamin D3 is the preferred supplement form because it is the form of vitamin D which most effectively treats vitamin D deficiency. The only way to know if a certain dosage works for you is to have your vitamin D levels tested, and continue monitoring your levels to determine the correct dose. Individual response to taking supplemental vitamin D3 varies from person to person so the amount needed to raise and/or maintain blood serum levels for one person may not be enough for another. This is due to various factors such as age, weight, absorption, overall health, and amount of sun exposure.

Matching Vitamin D3 with Vitamin K2

Always combine your vitamin D3 supplement with vitamin K2.

Studies show Vitamin K greatly enhances the benefits of vitamin D, in terms of bone strength and cardiovascular health. Vitamin D supports bone health by helping with calcium absorption. However, it is vitamin K that directs calcium to your skeleton, to prevent it from being deposited in the wrong areas.

Several different forms of vitamin K exist, with the primary form being vitamin K1, or phylloquinone, found primarily in green vegetables. Another form of vitamin K, known as vitamin K2 or menaquinone, is found primarily in animal products such as meat or eggs, as well as in foods such as cheese and natto, a fermented soy product. While most of the benefits of vitamin K were previously attributed to vitamin K1, recent research has identified important benefits for vitamin K2.

I prefer this Vitamin D3/K2 supplement.

In Health and Happiness,

Kelly Harrington, MS, RDN

Registered Dietitian Nutritionist for Healthy Goods


1. Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer. Int J Epidemiol. 1980 Sept; 9(3):227-31.

2. Yingya Ma, Trump D, Johnson CS. Vitamin D in combination cancer treatment.  J Cancer 2010; 1:101-107.

3. James SY, Mackay AG, Colston KW. Effects of 1,25 dihydroxyvitamin D3 and its analogues on induction of apoptosis in breast cancer cells.  J Steroid Biochem Mol Biol 1996;58:395-401.

4. Colston KW, Berger U, Coombes RC. Possible role for vitamin D in controlling breast cancer cell proliferation. 1989 Jan 28; 1 (8631): 188-91.

5. Oh EY, Ansell C, Nawaz H, Yang CH, Wood PA, Hrushesky WJ. Global breast cancer seasonality. Breast Cancer Res Treat. 2010 Aug; 123 (1): 233-43.

6. Grant WB. Update on Evidence that Support a Role of Solar Ultraviolet-B Irradiance in Reducing Cancer Risk.  Anticancer Agents Med Chem 2012 Oct 12.

7. Grant WB. Lower vitamin-D production from solar ultraviolet-B irradiance may explain some differences in cancer survival rates. J Natl Med Assoc. 2006 Mar; 98 (3): 357-64.

8. Grant WB, Peiris AN. Differences in vitamin D status may account for unexplained disparities in cancer survival rates between African and white Americans.  2012 Apr 1;4(2):85-94.

9. Grant WB. Relation between prediagnostic serum 25-hydroxyvitamin D level and incidence of breast, colorectal, and other cancers. J Photochem Photobiol B. 2010 May 12.

10. Garland CF, Gorham ED, Mohr SB, Garland FC. Vitamin D for cancer prevention: global perspective. Ann Epidemiol. 2009 Jul; 19 (7): 468-83.

The best way to test heavy metals.

Featured product

Hair Mineral Analysis Kit

Healthy Goods

Hair Mineral Analysis Kit


Recently viewed