It is recognized that vitamin D has many benefits for human health. Recently, it has been mentioned for its ability to strengthen the immune system and thus limit severe forms of COVID-19. Scientists now give it another power: vitamin D supplementation could reduce the risk of developing advanced cancer (metastatic or fatal).
Vitamin D is a liposoluble vitamin, synthesized by the body under the action of solar radiation. This endogenous origin also explains why, in our latitudes, a good number of individuals have vitamin D deficiencies in winter, when sunshine is scarce. To a lesser extent, it can also be provided by food, mainly by fish liver oil, so-called fatty fish (salmon, herring, sardines, mackerel, tuna, etc.), and dairy products. According to the National Agency for Food, Environmental and Occupational Health Safety, the nutritional reference for the population is 15 µg / day for an adult.
This vitamin plays several major roles in the body. It contributes in particular to the absorption of calcium and phosphorus by the intestines, and thus ensures the maintenance of a sufficient calcium level. As a result, it guarantees good mineralization of the skeleton and joints, efficient muscle contraction, as well as good nerve transmission. It is also involved in hormonal regulation and the activity of immune cells. And for several years, scientists have been trying to demonstrate its action on cancer cells.
No influence on the incidence rate
Previous studies have shown that people living near the equator, where exposure to the sun is greatest – and therefore, promotes vitamin D production – have lower incidence and death rates from certain cancers. Likewise, in experiments with cancer cells in vitro and in mice, vitamin D has been shown to slow the progression of cancer; it reduced the invasiveness of the tumor and its propensity to metastasize.
However, clinical trials in humans have not been able to categorically corroborate these results. Indeed, two years ago, the American VITAL study to examine the action of vitamin D and omega-3 on the body, found that vitamin D did not reduce the overall incidence of cancer. This study took place over a period of five years; it included more than 25,000 participants, aged 50 or over, who did not have cardiovascular disease or cancer when they were recruited.
This clinical trial aimed to assess the independent effects of vitamin D and omega-3 supplements, as well as the synergy between these two nutrients. The participants were therefore divided into four groups, each receiving some or all (or none) of these supplements: vitamin D (2000 IU per day) + omega-3 (1 g per day), vitamin D + placebo, omega-3 3 + placebo, then only placebos. The primary endpoints were major adverse cardiovascular events and cancer incidence.
The results showed no difference between the groups in cancer rates. In contrast, the figures suggested that vitamin D could lower the risk of death from cancer. Researchers at Brigham and Women’s Hospital have therefore investigated this potential link between taking vitamin D supplements and the risk of developing metastatic or fatal cancer.
In this new analysis, based on data from the VITAL trial, it appears that vitamin D is associated with an overall 17% reduction in the risk of advanced cancer. Better still: by only considering the data of participants with a normal body mass index (BMI), the risk reduction climbs to 38%. Body mass is therefore a factor influencing the action of vitamin D.
An action conditioned by the BMI
Paulette Chandler, physician and epidemiologist in Brigham’s preventive medicine division, and her colleagues set out to look specifically at the reduction in cancer deaths and the development of severe forms of cancer in participants with and without medication. vitamin D supplements. They also analyzed the potential influence of different categories of BMI (normal, overweight and obesity) on the action of this vitamin.
Of the 25,871 participants in the VITAL study, 1,617 were diagnosed with invasive cancer (breast, prostate, colorectal, lung, etc.) within the next five years. Of the approximately 13,000 participants who received vitamin D, 226 were diagnosed with advanced cancer; the number rises to 274 for the group that received the placebo. Additionally, of the 7,843 participants with a normal BMI (less than 25) taking vitamin D, only 58 were diagnosed with advanced cancer (compared to 96 in the placebo group).
The BMI results could be due to chance. However, there is previous evidence of the impact of body mass on the action of vitamin D. Randomized trials to analyze the impact of vitamin D on type 2 diabetes have found better action of vitamin D. vitamin D in people of normal weight; in obese people, on the other hand, vitamin D has shown no particular efficacy. Due to the volumetric dilution, people who are overweight or obese may need higher doses to gain benefit.
In addition, other studies in humans and animals have shown that immune function is impaired in obesity. Obesity has thus been associated with chronic inflammation and systemic deregulation of natural killer cell function. This inflammation could decrease the effectiveness of vitamin D by reducing the sensitivity of receptors for this vitamin, or by modifying its signaling.
Vitamin D deficiency is common in cancer patients; a study reports deficiency rates of up to 72%! Based on these new findings and previous studies on the subject, Chandler supports the idea that vitamin D supplementation could prevent metastatic cancer. Although the effects of this vitamin were modest, supplementation at the levels studied is much less toxic and less expensive than many current cancer therapies. The specialist adds that it would be interesting to conduct a complementary study to analyze more precisely the influence of BMI.