Should you worry about vitamin D deficiency? Maybe. Or maybe not.

Since my last blog post, where I shared my thoughts on BRCA1, BRCA2, and preventive mastectomies, I've been asked what else can a woman do to reduce her risk of breast cancer. I've heard a big deal about vitamin D, so I did a bit of research on the matter.

As a disclaimer, I should tell you up front that, though many correlations between vitamin D deficiency and cancer risk have been found, just as many have been refuted or found inconclusive. You can read more about it on the wikipedia page.

What is vitamin D?

The name "vitamin D" includes a group of steroid-like molecules (they are similar to steroids, but not quite steroids) that help our intestine absorb calcium and phosphates. Since calcium is essential in bone development, vitamin D deficiency has been most commonly associated to osteoporosis and other bone-related diseases. There aren't many foods rich in vitamin D, however, vitamin D can be endogenously synthesized when the skin is exposed to sunlight. Unfortunately, modern lifestyle keeps us cooped up many hours in office cubicles, or in the house during chores, or in malls. When we're out enjoying the sunshine we cover up with hats and super-protective sunscreens because we've been told that the sun is bad for the skin and can cause malignancies. As a consequence, vitamin D deficiency is increasing world-wide.

There is a foundation for all the studies that have analyzed correlations between several diseases, including cancers, and vitamin D: (i) several ecological studies have found a trend for an increase in incidence of certain cancers at higher latitudes, suggesting that longer exposures to the sun may have a protective effect. (ii) The vitamin D receptor (VDR) is expressed in many cells of the immune system, and mouse models have shown that vitamin D deficiency can promote certain auto-immune diseases. In a recent review, Sundaram and Coleman examine the link between vitamin D and influenza [Adv. Nutr. 2012 3: 517-525]. (iii) "VDR regulates a wide range of cellular mechanisms central to cancer development, such as apoptosis (cell death), cell proliferation (uncontrolled cell growth), differentiation, angiogenesis, and metastasis [1]". In line with this observation, Pereira, Larriba, and Munoz published a review on the evidence that vitamin D plays a protective role in colon cancer [Endocr. Relat. Cancer 2012 19: R51-R71].

In [1], Crew discusses the use of vitamin D supplementation as part of breast cancer prevention. She presents many interesting findings, for example:

"Colon, breast, and lung cancer have all demonstrated downregulation of expression of VDR when compared to normal cells and well-differentiated tumors have shown comparably more VDR expression as measured by immunohistochemistry when compared to their poorly differentiated counterparts. Higher tumor VDR expression has also been correlated with better prognosis in cancer patients [1]."

Crew looks at different types of studies: some suggest beneficial effects from using vitamin D (calcitriol) in combination with other anti-cancer treatments; some found an inverse association with mammography density, a biomarker for breast cancer (supposedly high density increases the risk of cancer); some found an inverse association between better breast cancer prognosis and vitamin D deficiency. However, many of these studies have limitations. For example, some only assess the levels of vitamin D through dietary intake, which is not a good measure of the circulating levels because it doesn't account for vitamin D synthesized through sun exposure. Some were confounded by obesity since fat is known to sequestrate vitamin D and also raise breast cancer risk. In light of all these considerations, Crew concludes:

"Even with substantial literature on vitamin D and breast cancer, future studies need to focus on gaining a better understanding of the biologic effects of vitamin D in breast tissue. Despite compelling data from experimental and observational studies, there is still insufficient data from clinical trials to make recommendations for vitamin D supplementation for breast cancer prevention or treatment [1]."

As I often do in my posts, rather than giving you answers, I make an effort to provide you with pointers and food for thought: in the end you have to make your own decisions about your health and the wellbeing of your family. As a personal note, I'll add that on my last blood report my vitamin D circulating levels were undetectable. I had no symptoms whatsoever, but I am now taking a vitamin D supplement. I'm also much less paranoid about smothering my kiddos with sunscreen when they play outside (which has made them much happier, two birds with one stone).

[1] Crew, K. (2013). Vitamin D: Are We Ready to Supplement for Breast Cancer Prevention and Treatment? ISRN Oncology, 2013, 1-22 DOI: 10.1155/2013/483687