A Recent Study on Vitamin D and Cancer Prevention

Vitamins and dietary supplements are widely used in Western countries and America. In particular, many people believe that vitamin D and omega-3 supplements are effective in preventing cancer and cardiovascular disease.

However, despite their popularity, this remains questionable. For vitamin D and omega-3 dietary supplements, the most comprehensive study conducted to date was the prospective (forward-looking) study of more than 25 thousand participants, the VITAL clinical trial (VITamin D and OmegA-3 TriaL), of vitamin D3 (cholecalciferol, 2000 IU / day) and marine omega-3 fatty acids (1 g / day). In this randomized, double-blind, placebo-controlled VITAL study, male participants aged ≥ 50 and female participants aged ≥ 55 were followed for 5.3 years.

In January 2019, NEJM published the study, which unexpectedly found that vitamin D3 and omega-3 supplementation did not reduce the risk of developing cancer or cardiovascular disease. This important study conducted by Manson and colleagues was disappointing for many people.

Scheduled to begin on May 29, the ASCO 2020 Virtual Congress featured the same VITAL study, with subgroup analysis results being shared. The study to be presented by Chandler and colleagues in the scientific program tested how vitamin D affected the incidence of advanced-stage (metastatic) cancer in individuals who did not have cancer or cardiovascular disease at baseline. The study also examined whether body mass index (BMI) modified these relationships.

The subgroup analysis reported a 17% reduction in the risk of developing advanced cancer among participants taking vitamin D3 supplements compared with placebo (HR 0.83, 95% CI [0.69, 0.99]; p = 0.036). When these results were classified by BMI, the reduction in cancer risk was greatest among those with a normal BMI (BMI < 25). However, this favorable effect was not observed in those who were overweight or obese (BMI > 25). Among those receiving omega-3 supplements, there was no interaction regarding the incidence of advanced cancer.

Chandler and colleagues interpreted the study results as indicating that vitamin D3 is a cost-effective, safe and accessible vitamin that could be used to reduce the incidence of advanced cancer. However, although this BMI subgroup analysis of the VITAL study was presented with a strong headline for the ASCO Congress, it appears little different from the disappointing results announced in 2019.

This study could not explain many uncertainties, including why vitamin D3 did not benefit people with a BMI > 25, whether the amount of vitamin D3 required varies by weight, and the existence of many additional mechanisms, including an impaired gastrointestinal (stomach and intestine) system and immune system. It also does not adequately establish the dose to recommend for cancer prevention in the general population. It can therefore be said that the study did not fully meet expectations. More convincing studies on vitamin D and cancer prevention are clearly needed. Until sufficient evidence is available, avoiding the use of vitamin D3 and omega-3 supplements to protect against cardiovascular disease and cancer would be an appropriate approach.