Vitamin D & Cancer: What Does the Science Say?

Vitamin D Basics

Vitamin D helps the body absorb calcium, maintain strong bones and muscles and help prevent bone-related diseases like osteoporosis. It also supports cell growth, immune function, and reduces inflammation.

Our bodies produce vitamin D when our skin is exposed to UVB rays from the sun. It is also found in foods like fatty fish, egg yolks, fortified dairy or plant-based alternatives, and as supplements (1,2,3,4).

Vitamin D & Cancer

Scientists are studying vitamin D and cancer because (1,5,6,7): 

• Many cancer cells have vitamin D receptors suggesting it could influence their behavior.
• It helps control cell division and was able to slow cancer cell growth in lab studies. 
• It can trigger the natural death of damaged cells (apoptosis).
• It could reduce blood vessel formation that tumors need to grow. 
• Its anti-inflammatory effects may be relevant, as inflammation is linked to cancer.

But lab findings don’t always translate to real life. Let’s dive into the science →

Vitamin D & Cancer Risk

While there is extensive research on vitamin D and cancer, the results remain inconsistent. Some studies suggest that low vitamin D levels may be linked to a higher risk of certain cancers, while others found no connection. Some research even suggests that higher vitamin D levels could be associated with an increased risk of certain cancers (6,8,9,10,11,12,13,14,15,16,17,18).

Vitamin D & Cancer Prevention

Large studies have tested whether vitamin D supplementation could lower cancer risk, but most found no significant difference between those who took vitamin D and those who did not. Overall, there is no strong evidence showing that vitamin D supplementation can prevent cancer (6,8,9,19,20,21,22,23,24,25,26,27,28,29,30,31).

Vitamin D & Cancer Treatment

There is no strong evidence that taking high-dose vitamin D helps treat cancer. Many studies examine vitamin D alongside standard treatments like chemotherapy or surgery, often comparing patients with and without vitamin D deficiency, making it difficult to determine if it has a real impact. Results have been inconsistent and vary depending on dosage and cancer types (32). While some research suggests a possible benefit, more research is needed to determine if vitamin D supplementation has any effect on cancer treatment or recovery (33,34,35).

Vitamin D & Cancer Mortality

Research on whether vitamin D levels affect cancer survival is inconclusive. Some studies found no clear link, while others showed mixed results. Higher vitamin D levels have been linked to worse cancer outcomes in some men, but not in women. A few analyses suggest that vitamin D supplements might slightly reduce cancer mortality, but the evidence is not strong and only found in specific cases. More research is needed (8,20,21,22,25,26,29,31,36,37,38,39,40,41,42,43).

Vitamin D Toxicity

While not getting enough vitamin D can cause health issues, too much can also be harmful. Vitamin D toxicity is rare but is usually caused by excessive or improper use of vitamin D supplements. It can lead to high calcium levels in the blood, causing nausea, weakness, kidney problems, and even heart issues. In severe cases, vitamin D toxicity can affect the nervous system, leading to confusion or agitation (44,45,46).

Plus, vitamin D can interact with some medications (46,47,48,49). Always talk to a healthcare provider before taking supplements.

Vitamin D & Cancer: Bottom line

Vitamin D is essential for bone health, immune function, and cell growth, but too much of it can be dangerous and its role in cancer remains unclear. More research is needed (9). 

What the current evidence says:

• Cancer Risk: Inconsistent results
• Cancer Prevention: No strong evidence
• Cancer Treatment: Insufficient support
• Cancer Mortality: Conflicting findings

While vitamin D deficiency should be addressed, it remains relatively rare (44,50,51). If you’re concerned about your vitamin D levels, talk to your healthcare provider.