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 that 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 that 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, which may be due to lower levels of vitamin D, attributed to lower production rates of vitamin D from solar UVB because of darker skin (7, 8).

Winter’s coming: 

As we enter the winter months and the strength of the sun’s rays diminish, 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. 

Getting the right dosage? 

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

The Vitamin D Council recommends the following amounts of supplemental vitamin D3 per day in the absence of proper sun exposure.

  • Healthy children under the age of 1 years – 1,000 IU
  • Healthy children over the age of 1 years – 1,000 IU per every 25 lbs. of body weight
  • Healthy adults and adolescents – at least 5,000 IU
  • Pregnant and lactating mothers - at least 6,000 IU+

For more information about vitamin D and breast cancer, please visit the Vitamin D Council's website at:

In Health and Happiness,

Kelly Harrington, MS, RD

Nutritionist for Healthy Goods



1.  Garland CF, Garland FC.  Do sunlight and vitamin D reduce the likelihood of colon cancerInt 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. Lancet. 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.  Dermatoendocrinol. 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.


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