Various epidemiological studies have revealed that people with higher blood levels of vitamin D have a reduced risk of developing colorectal cancer. If this observation arouses hope, because it suggests that a simple increase in the level of vitamin D, whether by exposing more to the sun, modifying its diet or taking food supplements – could decrease the risk of developing this disease. But reality is not so simple.
The potential role of vitamin D in the prevention and treatment of colorectal cancer arouses increasing interest – especially since this disease is increasing, especially in young adults. However, this is not a new field of research. Indeed, it has been known for a long time that low levels of vitamin D have been associated with an increased risk of developing colorectal cancer.
Demonstrated by epidemiological studies, this protective effect was however not confirmed by the controlled randomized trials set up to verify its existence. What conclusion is to derive from this apparently contradictory situation?
Effects highlighted by certain works
Vitamin D is synthesized in the skin in response to solar light. It has its biological effects via the vitamin D receptors (VDR) present throughout the organism, including in the fabric of the colon (the large intestine). When activated, these receptors help regulate genetic activity linked to inflammation, immune response and cell growth – central processes in the development and progression of cancer.
Read More: Risk factors to be avoided, food to favor … How to best protect yourself from colorectal cancer?
Preclinical studies have also shown that the active form of vitamin D (called calcitriol) can reduce inflammation, strengthen immune monitoring (the capacity of the immune system to detect abnormal cells), inhibit the growth of tumor blood vessels and regulate cell division – a key factor in cancer development, as has recently demonstrated my own research.
A large study, which involved more than 12,000 participants, notably revealed that people with low blood levels of vitamin D presented an increased risk of 31 % to develop colorectal cancer, compared to people whose levels of vitamin D were higher. Other works have also highlighted a 25 % reduction in the risk of colorectal cancer in individuals benefiting from food intake in vitamin D. Analysis of Health data ‘Health Study – a long -term study conducted with American nurses – indicates that women with the highest contribution in vitamin D had a risk of developing reduced colorectal cancer of 58 % the lowest contribution.
A literature review published in March 2025 also highlights the potential of vitamin D in the prevention and treatment of colorectal cancer. However, it also underlines the complexity and contradictions that persist in terms of knowledge on this subject.
Indeed, although observational data (which document vitamin D consumption by individuals) and mechanistic studies (which explore, in the laboratory, the way in which vitamin D works) suggest the existence of protective effects, the latter are not confirmed by controlled randomized trials. However, this type of test is currently the benchmark in terms of evaluation of the effectiveness of treatments.
-Mixed results during randomized trials
The randomized trials controlled consist in randomly assigning the participants a treatment (in this case, vitamin D) or a placebo, then comparing the results between the two groups. This approach in particular helps to eliminate potential biases, and to highlight cause and effect relationships.
Unfortunately, controlled randomized trials conducted to assess the effects of vitamin D on colorectal cancer have produced mixed results. Thus, the vital test – a large trial involving more than 25,000 participants – has not highlighted any significant reduction in the overall incidence of colorectal cancer in the case of a supplementation of 2,000 IU/day of vitamin D, over several years.
However, a meta-analysis of seven controlled randomized trials revealed an improvement of 30 % of survival in the face of this type of cancer thanks to vitamin D supplements. This result suggests that vitamin D could potentially be beneficial for patients, therefore during subsequent stages of the disease rather than prevention. But on the other hand, the results of the vitamin D/Calcium Polyp Prevention Trial did not show any reduction in the recurrence of adenomas (precancerous lesions) in participants who benefited from vitamin D supplementation, which leads to wondering which patients could really benefit from taking vitamin D, and what would be the effective doses …
Added to these uncertainties the question of causality: does a vitamin D deficiency contribute to the development of cancer? Or does the appearance of cancer reduce vitamin D levels in the body? It is also possible that the benefits observed are partly due to increased exposure to the sun, which could have independent protective effects of vitamin D.
Acquire an overview
The inconsistency of these results underlines the importance of considering the “totality of existing scientific evidence”, each study being only one of the pieces of a much larger puzzle. There are many biological effects that make vitamin D activity plausible. Observational and mechanistic studies suggest the existence of a significant link between this molecule and a reduction in the risk of colorectal cancer. However, clinical evidence is not yet solid enough to consider recommending vitamin D supplementation as a single prevention or treatment strategy for this disease.
Read More: Colorectal cancer: Who must be tested, and how?
That said, to ensure that within the population, the levels of vitamin D are correct (which means at least 30 ng/ml) can be judicious, because it is an inexpensive and low -risk public health measure. By combining it with other strategies, such as systematic and regular screening, a healthy diet, the practice of physical activity and personalized follow -up, vitamin D could play a precious role in the global prevention of cancer.
Its exact role in colorectal cancer remains to be specified. This molecule is not a miracle solution, but finds its place in a much wider table. Colorectal cancer is a complex disease, and fighting it requires an equally nuanced approach. For the moment, the warning it comes above all by the adoption of a lifestyle whose research has established, on the basis of solid evidence, the benefits, as well as regular screenings. Thus, of course, only by scientific monitoring, in order to keep yourself informed as new results are published.
