Vitamin D and Lower Cancer Risk

By: Mark Lange, PhD

Vitamin D is a fat-soluble prohormone – a substance the body can turn into a hormone – and this vitamin helps the body use calcium and phosphorus for strong bones and teeth. So what is the connection between vitamin D and cancer risk?

The Vitamin D Breakdown:

Like we mentioned, vitamin d is a prohormone that helps the body use calcium and phosphorus. Vitamin D3 is made by the body when skin is exposed to sunlight, which is then converted to 25-hydroxyvitamin D by the liver.   To evaluate a person’s vitamin D status, 25-hydroxyvitamin D in the blood is measured. While most people get inadequate vitamin D through sun exposure, there are dietary sources of vitamin d as well which include:

  • Fatty fish
  • Eggs
  • Milk
  • Fortified juices
  • Fortified cereals

Although sunlight may be the main source of vitamin D for most, it is also the main cause of skin cancer.  Naturally, everyone wants to know where the line is between getting enough sun and too much, but there is no such line quite yet. This is because the amount of time needed in the sun to make enough vitamin D is different for each person, and also depends on skin type, time of day, time of year and where you live.  Because of this, it’s not possible to give recommendations on exactly how much sun is needed to make the vitamin you need.

Thankfully, there are ways to know whether you might be at risk for a vitamin D deficiency. Those people who may be lacking vitamin D include:

  • People with naturally dark skin
  • People over the age of 65
  • People who are not often outdoors
  • People who wear clothes that cover up most of their skin while outdoors


Vitamin D and Lower Cancer Risk:

So what is the connection between vitamin D and cancer risk?

For many years, research indicated that the incidence and death rates for certain cancers were lower for people living in southern latitudes who were getting more sun exposure.  Based on data and observations, researchers hypothesized that vitamin D might be a reason why!  When they turned to animal studies, it was found that vitamin D actually restricted the development of cancer by slowing cancer cell growth and promoting cell death of cancer cells!

Researchers at Japan’s National Cancer Center and Shiga University of Medical Science looked at the relationship between circulating vitamin D concentration and the risk of overall and specific cancers.

A total of 33,736 participants were selected, with 3301 cancer patients and 4044 randomly selected subcohort participants.  Their 25-hydroxyvitamin D levels were measured and the participants were placed into one of four groups according to vitamin D level.  The vitamin D levels ranged between 36.9 nmol/L and 72.6 nmol/L.  The researchers found the risk of total cancer decreased as 25-hydroxyvtamin D level increased.

Despite the observation that a higher circulating concentration of vitamin D was associated to a lower risk of cancer, the researchers found that there was a ceiling effect where having a vitamin D concentration beyond an optimal level may provide no further benefit.  The researchers state that further dose-response studies are needed to find the optimal vitamin D concentration for cancer prevention.


Having blood tests to measure the amount of vitamin D in your blood is the only way to know if you’re getting enough vitamin D or not. The blood test you need is called a 25(OH)D blood test, just in case you’d like to ask your doctor!