Vitamin D deficiency and Breast Cancer Risk


As we transition from the fiery season of Summer to the Harvest and abundance of Airy Fall the days grow shorter and the sunlight (for most of us in the Northern Hemisphere) is limited. Limiting our exposure to sunlight also limits our exposure to Vitamin D. It only takes 15 minutes of unprotected sunlight to build up your stores of Vitamin D.

Food Sources High in Vitamin D:

  • Egg Yolks
  • Fatty Fish
  • Cheese
  • Fortified products (milk/almond milk, OJ)
  • Mushrooms
  • Tofu 

Doesn't leave vegans with a lot of options unless they are eating loads of mushroom-tofu stir fry or something. Sure there are many other sources of Vitamin D that you can get from your diet, but the vitamin D from the sun is more easily regulated by the body and is free when you have access to sunlight. Another benefit of gaining vitamin D from sunlight is you can't overdose, your body naturally regulates this process and won't convert extra D that isn't needed.

In Northern latitudes where sunlight exposure becomes limited in the winter months Women should consider supplementing with Vitamin D to keep their stores high. A majority of people in the US (50-74%) are already deficient in Vitamin D. (Imitaz et al. 2012.) Especially women with darker skin tones as they do not absorb/convert as much D from the sun and should consider supplementing with Vitamin D3 orally. 

In college I wrote my thesis on Vitamin D Deficiency and its correlation to chronic diseases, specifically breast cancer. Through my research I became a huge advocate for proper Vitamin D supplementation. 


Below is an excerpt from my paper if you want the nitty gritty and to read about some of the research suggesting the correlation between breast cancer and Vitamin D deficiency. If you are not a science nerd you can scroll to the bottom where I summarize my findings in layman's terms. 



 Recent studies suggest that our RDA (recommended daily allowance) for vitamin D should be increased substantially from its current value of 600 IU/day. It is known that vitamin D plays a strong role in bone health and deficiency is linked to osteomalacia and “rickets”, but the more it is investigated, the more it appears to have a possible link in other diseases. Vitamin D deficiency has been implicated in such diseases as osteoporosis, multiple sclerosis, juvenile diabetes, diabetes mellitus, schizophrenia, hypertension, impaired immune function, and cancer. Recently, breast cancer in particular has become a focus of many research studies seeking to determine if there is a connection between vitamin D and breast cancer risk. The following review analyzes vitamin D’s association with breast cancer by analyzing skin color, sunlight exposure, and vitamin D supplementation in breast cancer patients. 


Sources of Vitamin D

           Vitamin D can be acquired through dietary sources such as animal, fish, dairy and D- fortified products in the form of vitamin D3 (cholecalciferol). It is then activated in the liver and hydroxylated to its active form, 25 (OH) D3, which can be utilized throughout the body.
           Vitamin D can also be obtained through the skin. Ultraviolet-B (UVB) photons from the sun are absorbed by steroid 7-dehydrocholesterol in our skin; pre-vitamin D3 (cholecalciferol) is then formed. The body can then utilize pre-vitamin D3 made from the skin. Sunlight is a significant source of vitamin D that can be easily acquired, just 15 minutes of un-protected sun exposure can produce 10,000 IU of Vitamin D (Holick 2004). People living at northernmost latitudes, and southernmost latitudes (above 35 degrees north and below 35 degrees south) do not get the same amount of exposure to sunlight in the winter months because the UVB photons are absorbed by the ozone layer, preventing vitamin D3 production (Holick 2004). People at these latitudes therefore run the risk of lowered vitamin D status, which is being hypothesized in multiple studies to lead to increased risk for disease.

Breast Cancer

           According to the U.S. breast cancer statistics, “About 1 in 8 U.S. women (just under 12%) will develop invasive breast cancer over the course of her lifetime” ( Although rates of breast cancer in American women has been decreasing slightly every year since 1990, it has the highest mortality rates than any other cancer each year among women. More controllable risk factors should be evaluated, such as vitamin D supplementation, because of its potential to decrease breast cancer risk.

Vitamin D activity in Breast Tissue

A study performed by researchers from the Breast Cancer Genetics Group comparing paired non-malignant and malignant human breast tissue found that vitamin D could function and thrive in isolated breast tissue. The study by Suetani et Al. (2012) took three samples of breast tissue, a malignant breast tissue sample, a non-malignant breast tissue sample near tumors of a woman with breast cancer, and non-malignant breast tissue from healthy women receiving cosmetic breast surgery. The samples were explanted and tested for malignancy. The inactive form of vitamin D (25[OH]D3) was added to the samples.
           The results showed that the gene that converts vitamin D to its metabolically active form and vitamin D receptor (VDR) protein expression continued and did not diminish in the explanted tissue samples. Overall, there was a reduced response to pre-vitamin D in the malignant cells indicating a dysregulation of vitamin D metabolism in breast cancer tissue. This study indicates that breast tissue has the metabolic potential to convert pre-vitamin D to its metabolically active form locally, supporting a relationship between vitamin D and breast cancer.

A different study analyzing serum vitamin D status taken from a multi-ethnic group of breast cancer survivors found that almost all of the women had sub-optimal levels of vitamin D. Levels of vitamin D were significantly different among races, with the lowest levels found in African American women (Neuhouser et al. 2008). Again, this could be due to the decreased ability of darker skin pigmentations to synthesize vitamin D through sunlight. 

Vitamin D status is not only below optimal levels in northern latitudes, but also in many parts of the world including third world countries. A study evaluating Vitamin D deficiency in breast cancer patients in Southeast Asia found that almost all of the women in the study, breast cancer and healthy controls alike, had vitamin D deficiency (Imitaz et al. 2012). The healthy population of Southeast Asia had 70-97% vitamin D deficiency, which was comparable to the healthy population of the US at 50-74%. Nearly all of the breast cancer patients in the study spent a majority (92%) of their time indoors. According to Imitaz et al. (2012) the diminished vitamin D status of the breast cancer patients was probably due to the time spent indoors. This study asserts the importance of sunlight exposure to vitamin D status.
           A review by Bray (2004) recognized the changing global patterns of breast cancer. It identified the highest incidence of breast cancer in the northern latitudes, where vitamin D status is lowest. Also, increased mortality rates were found in Black women, who were unable to acquire sufficient vitamin D through the skin. This suggests that vitamin D status could be a modifiable risk factor for breast cancer. Vitamin D status is especially important for those at risk for diminished vitamin D deficiency in northern latitudes and with darker skin pigmentation. With an inverse association between vitamin D and breast cancer risk having been established, research sought to determine how to balance the dangers associated with unprotected sunlight exposure with the benefits of acquiring vitamin D from the sun. 

A study performed by Stalgis-Bilinski et al. (2011) sought to discover how to achieve this balance. The goal of the study was for participants to acquire 1,000 IU of vitamin D per day within 30 minutes with 11-17% of unprotected skin exposed (arms, hands, face). The results found that fair skinned people could achieve this goal within 30 minutes with only 11% of unprotected skin exposed. Increased levels of vitamin D can be achieved in less than 30 minutes when more unprotected skin is exposed depending on the time of day. As previously mentioned vitamin D is acquired through UVB rays, which are highest during the middle of the day. Unprotected sunlight exposure should be avoided early in the day and late in the day when deep, skin penetrating UVA rays are strongest because of their association with skin cancer risk (Stalgis-Bilinski et al. 2011). Sunlight exposure should be recognized as a significant source of vitamin D.



In a nutshell: 

  • Sun exposure is an excellent source of Vitamin D, aim for 20 minutes of unprotected sunlight during the hours between 10AM-2PM when UVB rays are most prevalent and skin cancer causing UVA rays aren't as strong. 
  • The shadow trick: Supplement your body with vitamin D from sun exposure only when your shadow is shorter than you (generally 10AM-2PM and this won't happen in the winter months in higher latitudes so supplement orally with D3). 
  • Vitamin D can be converted to its active form in isolated breast tissue and plays a role in normal breast cell growth, having the potential to prevent breast cancer cells from growing when Vitamin D is present in the cell. 
  • Make sure if you take an oral supplement of Vitamin D it is D3 (NOT D2).
  • The darker your skin color the less vitamin D you produce from the sun, so those with darker skin tones should supplement with vitamin D3 orally. 
  • Check with your doctor before supplementing with Vitamin D as too much oral vitamin D can cause high levels of Calcium in the blood (toxicity only occurs if someone is taking greater than 10,000 IU of vitamin D consistently for a few months...) and remember you can't overdose on Vitamin D from sunlight, but can get too much sun exposure especially during times of high UVA rays (before 10AM and after 2PM).  

The bottom line: Spending hours basking in the sun is bad for your skin and puts you at risk for cancer, but the sun shouldn't be completely avoided like the plague. Take your vitamin D levels seriously and either supplement with oral D3 or allow yourself 20 minutes of sun exposure a few times a week in the summer months. 

Dr. Mercola is a great resource to learn more about the importance of Vitamin D here is just one of his many articles about Vitamin D.



  • Holick, MF, Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers and cardiovascular disease. Am. J. Clin. Nutr.  2004; 79:364. 
  • Imtiaz, S, Siddiqui, N, Raza, SA, Loya, A, Muhammad, A. Vitamin D deficiency in newly diagnosed breast cancer patients. Indian J of EndocrinolMetab 2012; 16(3):409-413. 
  • Neuhouser, ML, Sorenson, B, et al. Vitamin D insufficiency in a multiethnic cohort of breast cancer survivors. Am J Clin Nutr. 2008; 88(1):133-139. 
  • Stalgis-Bilinski, KL, Boyages, J, Salisbury, EL, Dunstan, CR, Henderson, SI, Talbot, PL. Burning daylight: balancing vitamin D requirements with sensible sun exposure. MJA. 2011; 194 (7):345-348. 
  • Suetani, RJ, Ho, K, Jindal, S, et al. A comparison of vitamin D activity in paired non-malignant and malignant human breast tissues. 2012. Elsevier. Molecular and Cellular Endocrinology 362 2012; 202-210. 
  • "U.S. Breast Cancer Statistics." N.p., n.d. Web. 09 Dec. 2012.