Common pill taken by millions every day 'could help lower cancer risk'

A pill that millions of people take daily could potentially lower the risk of cancer, new research suggests. Vitamin D, which is readily available as a supplement on the High Street and online, has previously been associated with a reduced risk of colorectal cancer (CRC).

One study involving over 12,000 participants discovered that those with low blood levels of vitamin D had a 31% higher risk of developing CRC compared to those with higher levels. Another study reported a 25% lower CRC risk among individuals with high dietary vitamin D intake.

Furthermore, data from 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, reports .

Justin Stebbing, Professor of Biomedical Sciences at Anglia Ruskin University, said: "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."

The human body naturally produces vitamin D when exposed to sunlight. Vitamin D receptors (VDRs), which are found throughout the body including in colon tissue, play a crucial role in controlling gene activity related to inflammation, immune response and cell growth – all of which are central to the development and progression of cancer.

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Professor Stebbing shared with : " 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." Professor Stebbing revealed that randomised controlled trials (RCTs) on vitamin D and CRC have yielded inconsistent results.

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The VITAL trial – involving more than 25,000 participants – discovered no significant reduction in overall colorectal cancer incidence with 2,000 IU/day of vitamin D supplementation over several years. But a review of seven studies did show that vitamin D supplements improved bowel cancer survival rates by 30%, indicating possible benefits later on in the disease rather than preventing it.

Professor Stebbing said: "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."

He added: "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.

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"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."