Vitamin D deficiency is implicated in several common diseases, including cancer. Most cancer-related vitamin D studies focus on it’s potential in cancer prevention, but today we’ll look at the effect of vitamin D levels on recurrence of cancer – specifically colorectal cancer. 

Many people are deficient in vitamin D and the numbers increase dramatically during the winter months when we get outside less and there is less sunshine. I’ve written several blog posts before on vitamin D as being a biomarker for cancer – see the links at the bottom of this blog post. These posts detail how to test your vitamin D levels and what level you should be aiming for. 

The importance of Vitamin D is highlighted in a study looking at survival after colorectal cancer in relation to plasma vitamin D levels. Colorectal cancer is also known as colon cancer, rectal cancer and bowel cancer. Let’s see what the study looked at and found. 

The infographic below summarizes the study design and results.

Infographic on study on Vitamin D levels affect survival after colon cancer diagnosis from

Study design positives

There are several good things about this study.

  1. They didn’t rely on people saying how much vitamin D supplementation they had or sun exposure. They actually looked at their plasma vitamin D levels. Many studies don’t do this.
  2. They measured the plasma levels at the time of surgery.  Other studies typically measure it before cancer diagnosis – often years before. 
  3. The study was not a randomized clinical trial so it cannot yield results saying something ’caused’ something else.  It can only say that Vitamin D levels correlated with survival. However, by adding in the gene polymorphism aspect, the finding that several of these alleles were seen to be protective, gives more weight to the evidence that Vitamin D level could be what impacts survival.

Colorectal cancer

Colorectal cancer is the third most frequent cancer worldwide, with an estimated 1.2 million cases, yet it is potentially largely preventable.

There were some differences in response in this study depending on the stage of the CRC cancer. The group most impacted by higher Vitamin D levels was those with stage II CRC. Compared to stage III CRC, fewer stage II patients have chemotherapy so this may account for some of this difference.  

Vitamin D levels

The vitamin D levels seen in this study were generally low. The study was conducted in Scotland, an area not known for its sunny weather!  

But dietary vitamin D intake is low in many populations, even in those taking supplements.  This means that skin synthesis during exposure to sunlight is frequently our major source of vitamin D. Such synthesis is influenced dramatically by geographical latitude and weather. Our modern lifestyle also compounds the deficits as we spend more time indoors.  Is this a slippery slope and we are becoming more and more vitamin D deficient?  

Take home message

The results of this study suggest that vitamin D levels correlate with survival rate and rate of recurrence in colorectal/bowel cancer patients. If you have had CRC, it would seem prudent to check your levels every winter, at least, and ensure that you are not deficient.  If you are deficient, consider supplementation. See the posts below for testing and recommended levels.

But this applies to more than those with CRC. Vitamin D deficiency seems to be a factor in many different diseases, including different types of cancer. Winter time sees a rise in deficiency as people spend less time outdoors. Why not get your vitamin D level tested and see if you need to add some supplementation or safely increase your sun exposure. Here are a couple of other blog posts to check on vitamin D that talk about what level of supplementation is needed and how to get tested. 

Cancer biomarkers worth following | Vitamin D

Vitamin D levels and breast cancer prognosis: The importance of testing

Dminder app to follow your vitamin D levels 

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