The potential role of vitamin D in preventing and treating colorectal cancer (CRC) has attracted growing research interest – especially as CRC rates are rising, particularly among younger adults . This isn’t a new area of study. Low vitamin D levels have long been linked to a higher risk of developing colorectal cancer.
Author
- Justin Stebbing
Professor of Biomedical Sciences, Anglia Ruskin University
One large study involving over 12,000 participants found that people with low blood levels of vitamin D had a 31% greater risk of developing CRC compared to those with higher levels. Similarly, another study reported a 25% lower CRC risk among individuals with high dietary vitamin D intake.
Data from the Nurses’ Health Study – a long-term investigation of American nurses – showed that women with the highest vitamin D intake had a 58% lower risk of developing colorectal cancer compared to those with the lowest intake.
Now, a review highlights vitamin D’s promise in colorectal cancer prevention and treatment – but also underscores the complexity and contradictions in current research.
While observational data , which follow people’s use of vitamin D, and mechanistic studies , to investigate how vitamin D works in the laboratory, suggest protective effects, this isn’t confirmed by larger trials.
In fact, randomised controlled trials ( RCTs ), in which some people receive vitamin D and others don’t, the gold standard by which treatments are judged, reveal inconsistent outcomes. This highlights the need for a balanced approach to its integration into public health strategies.
Vitamin D is synthesised in the skin in response to sunlight and exerts its biological effects through vitamin D receptors (VDRs) found throughout the body, including in colon tissue. When activated, these receptors help regulate gene activity related to inflammation, immune response and cell growth – processes central to cancer development and progression.
Preclinical studies have shown that the active form of vitamin D (calcitriol) can suppress inflammation, boost immune surveillance (the immune system’s ability to detect abnormal cells), inhibit tumour blood vessel growth and regulate cell division – a key factor in cancer development, as demonstrated in my recent research .
Epidemiological studies , which track health outcomes across large populations over time, consistently find that people with higher blood levels of vitamin D have a lower risk of developing CRC. This paints a hopeful picture, suggesting that something as simple as getting more vitamin D – via sun exposure, diet, or supplements – could lower cancer risk.
But the story gets more complicated.
Mixed results
When it comes to medical decision-making, randomised controlled trials (RCTs) are the gold standard. These studies randomly assign participants to receive either a treatment (like vitamin D) or a placebo, helping eliminate bias and isolate cause-and-effect relationships.
Unfortunately, RCTs on vitamin D and CRC have produced mixed results.
For example, the VITAL trial – a major RCT involving over 25,000 participants – found no significant reduction in overall colorectal cancer incidence with 2,000 IU/day of vitamin D supplementation over several years.
However, a meta-analysis of seven RCTs did show a 30% improvement in CRC survival rates with vitamin D supplements, suggesting potential benefits later in the disease course rather than for prevention.
On the other hand, the Vitamin D/Calcium Polyp Prevention Trial found no reduction in the recurrence of adenomas (pre-cancerous growths) with supplementation, raising questions about who benefits most, and at what dosage.
Adding to the uncertainty is the question of causation . Does low vitamin D contribute to cancer development? Or does the onset of cancer reduce vitamin D levels in the body? It’s also possible that the observed benefits are partly due to increased sunlight exposure , which itself may have independent protective effects.
The big picture
These discrepancies highlight the importance of considering the “totality of evidence” – treating each study as one piece of a larger puzzle.
The biologic plausibility is there. Observational and mechanistic studies suggest a meaningful link between vitamin D and lower CRC risk. But the clinical evidence isn’t yet strong enough to recommend vitamin D as a standalone prevention or treatment strategy.
That said, maintaining sufficient vitamin D levels – at least 30 ng/mL – is a low-risk, cost-effective health measure. And when combined with other strategies like regular screening, a healthy diet, physical activity, and personalised care, vitamin D could still play a valuable role in overall cancer prevention.
Vitamin D is not a miracle cure – but it is part of a much broader picture. Its role in colorectal cancer is promising but still being defined. While it’s not time to rely on supplements alone, ensuring adequate vitamin D levels – through sun exposure, diet, or supplements – remains a smart choice for your health.
Colorectal cancer is a complex disease, and tackling it requires an equally nuanced approach. For now, that means focusing on evidence-based lifestyle changes, regular screenings, and staying informed as new research unfolds.
