Higher-dose vitamin D supplementation may improve outcomes in colorectal cancer

Patients with colorectal cancer often have vitamin D deficiency and chronic inflammation. These are factors that not only increase the risk of developing the disease but also worsen prognosis. However, higher-dose vitamin D supplementation appears to reduce a key inflammatory marker associated with disease progression and poor outcomes, according to a German randomized, double-blind, placebo-controlled study published in the British Journal of Cancer.

Colorectal cancer is among the most common types of cancer and is associated with significant morbidity. Globally, it accounts for nearly one million deaths each year.
The disease is linked to chronic inflammation, which contributes to oxidative stress - a condition in which free radicals can damage cells and tissues in the colon.
Vitamin D deficiency is highly prevalent among patients with colorectal cancer, yet it is not standard practice to treat these patients with vitamin D to optimize their blood levels of the vitamin.
However, there is growing scientific interest in the therapeutic potential of vitamin D in colorectal cancer. Although randomized controlled trials (RCTs) have been limited, a recent meta-analysis suggests that patients receiving vitamin D supplements have improved outcomes, including enhanced response to chemotherapy and fewer side effects.
The new German randomized, double-blind study examined the effects of higher-dose vitamin D supplementation in colorectal cancer patients, with particular focus on inflammatory biomarkers.
The study included 126 patients with colon or rectal cancer. All had undergone surgery within the previous year, and their blood levels of vitamin D were under 60 nmol/L, which is considered low.
Participants were divided into two groups: one group received a higher dose of vitamin D corresponding to 50 micrograms (2,000 IU) daily, which is well above the official recommendations of 5–20 micrograms, while the other group got a placebo. Neither participants nor researchers knew who received which treatment. The study lasted 12 weeks and showed the following:

• The vitamin D group achieved a 40% (statistically significant) reduction in the inflammatory biomarker IL-6 compared with the placebo group
• There were no statistically significant differences in the markers IFN-γ (which initiates immune responses) or MMP-1 (which breaks down collagen)

The researchers conclude that colorectal cancer patients with vitamin D deficiency who receive higher-dose supplementation experience a reduction in IL-6, a marker associated with improved prognosis. Supplementation aimed at optimizing vitamin D blood levels may therefore represent a relevant and novel therapeutic approach for patients with colorectal cancer.
The German study is consistent with a growing body of research showing that vitamin D may counteract cancer through multiple mechanisms.

Vitamin D has several cancer-protective properties

Vitamin D plays a critical role in the immune system, which helps identify and eliminate abnormal cells such as cancer cells. It also regulates inflammatory processes, which are often dysregulated in various cancers. As noted, chronic inflammation can damage cells, including their DNA and energy-producing mitochondria.
In addition, researchers at Aalborg University (Denmark) have conducted a mouse study showing that vitamin D may exert anticancer effects by influencing specific gut bacteria.
There is therefore a clear link between vitamin D, the immune system, the gut microbiota, and various cancers, including colorectal cancer.
A large-scale analysis of 1.5 million Danes has also demonstrated a clear association between low blood levels of vitamin D and an increased risk of developing several types of cancer. The findings further suggest that current recommendations for vitamin D intake are often too low to optimize blood levels, which ideally should exceed 75 nmol/L.
Moreover, maintaining optimal vitamin D levels may enhance the effectiveness of chemotherapy and immunotherapy, reduce hospitalizations, and overall improve prognosis across multiple types of cancer.

References:

Tafirenyika Gwenzi et al. Effects of personalized Vitamin D3 on inflammation in colorectal cancer patients. British Journal of Cancer. 2026

Nina Hermansen. Forskning påviser sammenhæng mellem lavt D-vitamin og højere risiko for kræft. Aalborg Universitet. Lagt online: 28.04.2024

Paulette D Chandler et al. Effect of Vitamin D3 Supplements on Development of Advanced Cancer. JAMA 2020