Daily vitamin D supplementation is associated with a dramatic reduction in the risk of recurrence of digestive cancer that expresses an inactive version of an important tumor suppressor gene.
In contrast to other vitamins, which can be easily absorbed through food, vitamin D occurs rarely in nature and is mainly produced by the skin’s exposure to sunlight. This peculiarity has a significant impact on cancer, as numerous studies have found that vitamin D deficiency can promote the development of certain types of cancer, particularly of the digestive system.
For example, it has been observed that mortality associated with colorectal cancer is highest in people who are least exposed to sunlight, such as those living in large cities or in high-latitude regions. This effect is likely due to vitamin D deficiency, as subsequent epidemiological studies found that high blood levels of this vitamin (greater than 25 ng/ml) were associated with a much lower risk of colorectal cancer1.
Interindividual variations
These observations paved the way for several clinical trials aimed at determining whether vitamin D supplementation could be associated with a reduction in cancer incidence.
Overall, the results of these studies are rather mixed, as we were unable to demonstrate a major preventive effect of vitamin D when examining cancer incidence in the population studied.
However, a closer analysis shows that certain people are much more likely to benefit from the anti-cancer effects of this vitamin.
For example, one study showed that lean people (BMI ≤ 25) who took 2000 IU of vitamin D supplements for 5 years had a lower risk of developing advanced cancer, with a 38% reduction compared to the previous study. Placebo, while this protection was insignificant in overweight people and disappeared completely in obese people2.
Cancer subtypes
A recent study provides another example of this varying effectiveness of vitamin D’s cancer-fighting effects depending on the person3.
In this study, researchers examined the effect of a 2000 IU supplement on colorectal cancer recurrence and mortality based on the presence of an abnormal form of the p53 protein in cancer cells.
The p53 gene, called the guardian of the genome because of its ability to maintain DNA integrity, is very often mutated during cancer development and the resulting protein is inactive and unable to curb abnormal growth of tumors.
The researchers recruited 392 patients with digestive cancer, mainly colon cancer (47%), stomach cancer (43%) and esophageal cancer (9%), including 142 of them who had cancer with an inactive p53. The patients were randomly divided into a control group (placebo) and a vitamin D group (2000 IU per day) and then followed for a period of 5 years.
The results are truly spectacular: in cancer patients containing inactive p53 protein, supplementation with 2000 IU was associated with a 5-year survival rate without cancer recurrence of 81%, compared to just 31% in the placebo group.
Given the very high proportion of cancers that contain defective p53, these results suggest that patients battling cancer may benefit greatly from normalizing their blood levels of vitamin D through supplements.
It is generally considered that a daily dose of 2000 IU is required to achieve optimal vitamin D levels of approximately 30 ng/ml.
♦ 1. Garland CF et al. Serum 25-hydroxyvitamin D and colorectal cancer: eight-year prospective study. lancet 1989; 2:1176-8.
♦ 2. Chandler PD et al. Effect of vitamin D3 supplements on the development of advanced cancer: a secondary analysis of the VITAL randomized clinical trial. JAMA network opened. 2020; 3:e2025850.
♦ 3. Kanno K et al. Effect of vitamin D supplements on relapse or death in a p53-immunoreactive subgroup with digestive tract cancer: post hoc analysis of the AMATERASU randomized clinical trial. JAMA network opened. 2023;6(8):e2328886.