A 2025 review paper highlighted the evidence showing the relationship and mechanisms by which optimal vitamin D status is linked to the prevention of colorectal cancer (1). In fact, quite recently the Nurses’ Health Study showed that nurses with the highest vitamin D intake had a 58% lower risk of developing colorectal cancer compared to those with the lowest intake. Other studies have shown similar results, whereby higher vitamin D intake or maintaining a blood vitamin D level at or above 75 nmol/L (30 ng/ml) was associated with a 25-33% decreased risk of developing CRC, compared to individuals with lower intake or blood levels (2). Colorectal cancer (CRC) is the second most common cancer in men and the third most common cancer in women. As the researchers point out, over the past decades, the global incidence of CRC has increased significantly, largely due to the rising case numbers in developing countries. The growing adoption of Western dietary and lifestyle patterns in these regions has played a major role in this trend. They point to strong evidence showing that a sedentary lifestyle, along with a diet high in certain fats, red meat, and low in fiber significantly contribute to accelerated aging and CRC development. Of course, certain genetic risk factors play a role in a small number of cases, but most of the increase in CRC appears to be related to faulty dietary and lifestyle factors. Additionally, inflammatory bowel diseases, obesity, frailty, and diabetes, also elevate CRC risk.

One of the lifestyle factors that appears to modulate the risk of CRC involves vitamin D nutritional status. The researchers review the evidence showing that sub-optimal blood vitamin D levels are strongly linked to an increased risk of CRC. Preclinical studies have shown us the multitude of ways that vitamin D helps to defend against CRC. For instance, vitamin D plays a key role in immunomodulation by reducing inflammation, suppressing autoimmune responses, and supporting the function of immune cells. It also impacts cell division rates and maturation of cells (proliferation and differentiation), inhibiting uncontrolled cell growth and it encourages cancer cells to revert to a more normalized appearance and slow their replication rate. And since many tumor cells express vitamin D receptors, vitamin D can directly exert anti-tumor effects. Furthermore, vitamin D inhibits angiogenesis—the formation of new blood vessels that support tumor growth—and promotes apoptosis, or programmed cell death, both of which are critical in cancer suppression.

In the words of the researchers, “Adequate vitamin D levels influence gene expression related to inflammation and cell proliferation, inhibiting tumor development. Vitamin D also activates mechanisms that suppress cancer cell survival, proliferation, migration, and metastasis. Low levels of vitamin D have been associated with an increased risk of CRC, with deficiency correlating with higher disease incidence. Lifestyle factors, such as a diet high in red meat and calories but low in fiber, fruits, and vegetables, as well as physical inactivity, contribute significantly to CRC risk. Insufficient calcium and vitamin D intake are also linked to disease occurrence and poorer clinical outcomes. Maintaining optimal vitamin D levels and adequate dietary intake is crucial in preventing CRC and improving patient prognosis”.

They go on to cite studies showing that vitamin D supplementation has been used successfully to reduce the incidence of colon polyps (precancerous lesions) in high-risk patients. The researchers also remind us that more optimal vitamin D status is also important for heart health, blood pressure and metabolic health (helping us burn fat, keep our blood sugar more normalized, reducing diabetes risk) and it helps keep our immune system strong – warding off respiratory infections. It helps to prevent osteoporosis, which affects one in four women over 50 and one in eight men over 50.  Vitamin D is also required by the brain and nervous system whereby more optimal vitamin D blood levels and vitamin D supplementation studies have shown its importance in helping to prevent and possibly treat age-related dementia and Alzheimer’s disease, preserving cognitive function. It may reduce the risk of depression (as they also add).  Vitamin D also helps to support the gut microbiome and reduces bowel inflammation, helping to reduce risk of inflammatory bowel diseases. Vitamin D also supports normal thyroid function (1). Vitamin D also stimulates the cell’s longevity circuit Sirtuin genes, linked to anti-aging, longevity and prevention of many age-related degenerative diseases (3).

Vitamin D is not a miracle drug or a panacea, but experts agree that it plays a very important modulating role in the health maintenance, disease prevention and longevity. What is very alarming, as they highlight, is the world-wide prevalence of low vitamin D levels (1). This included many populations in North America, Europe, Asia, extending to most countries around the world.  The bottom line is that most people would benefit from achieving a blood vitamin D level of between 75 – 125 nmol/L, according to many experts (30-50 ng/ml). And as one review paper pointed out, most healthy people can achieve these levels by supplementing with 1,000-2,000 IU of vitamin D per day, which is considered a safe and effective dosage (4).I will also point out that the importance of vitamin D in gut health was also highlighted in the May 20, 2025, Medscape review article entitled, The Overlooked Link Between Vitamin D and GI Health, which should be a must read for all doctors (5).

I have included the references for this information in the text below.

References:

Fekete M et al. Vitamin D and colorectal cancer prevention: Immunological mechanisms, inflammatory pathways, and nutritional implications. J Nutrients,2025;17(8): 1351. Vitamin D and Colorectal Cancer Prevention: Immunological Mechanisms, Inflammatory Pathways, and Nutritional Implications

Can vitamin D help prevent colorectal cancer” The science is promising – but not straightforward. The Conversation. May 2, 2025. https://theconversation.com/can-vitamin-d-help-prevent-colorectal-cancer-the-science-is-promising-but-not-straightforward-255025#:~:text=Data%20from%20the%20Nurses’%20Health,those%20with%20the%20lowest%20intake.

Nemeth Z et al. Interplay of vitamin D and SIRT1 in tissue-specific metabolism- potential roles in prevention and treatment of non-communicable diseases including cancer. Int J Mol Sci, 2023;24(7): 6145 Interplay of Vitamin D and SIRT1 in Tissue-Specific Metabolism—Potential Roles in Prevention and Treatment of Non-Communicable Diseases Including Cancer

Pludowski P et al. Vitamin D supplementation: A review of the evidence arguing for a daily dose of 2,000 IU (50 ug) of vitamin D for adults in the general population. J Nutrients, 2014;16(3): 391 https://pubmed.ncbi.nlm.nih.gov/38337676/

Medscape 2025 Vitamin D and GI Health:
The Overlooked Link Between Vitamin D and GI Health

Eat Smart, Live Well, Look Great,
Dr. Meschino