Vitamin D has long been known as a key vitamin in supporting our bone health by aiding the absorption of calcium . Recent studies have also suggested that vitamin D may play a role in influencing our immunity . Read on to find out more about a recently published large-scale trial that investigated the effects of vitamin D supplementation on the risk of cancer.
Vitamin D, also known as calciferol, is a naturally occurring fat-soluble vitamin in our body. It is produced in our bodies when we are exposed to ultraviolet (UV) rays and can also be found in foods and supplements. Vitamin D undergoes a 2-step activation process to become fully activated in our body, first by the liver and then by the kidneys . It ranks among one of the most widely used supplements, especially in older adults for bone health .
The VITamin D and OmegA-3 TriaL (VITAL) trial was a randomized clinical trial that aimed to investigate the effects of vitamin D and omega-3 fish oil supplementations on cancerand cardiovascular diseases (CVD) prevention .
The authors also conducted a meta-analysis of the current trials relating to vitamin D together with the VITAL trial to further observe the effects of vitamin D supplementation on cancer and CVD endpoints.
Results from the VITAL trial
The VITAL trial found that vitamin D showed a promising signal for reducing cancer mortality. Although vitamin D did not reduce total overall cancer incidence, subgroup analyses discovered that individuals with normal body mass index (BMI) had a significant reduction in cancer risk. African Americans also had a potential signal in cancer risk reduction as well.
This result also corroborated with earlier trials such as the Randomized Evaluation of Calcium or vitamin D (RECORD) trial , which suggested vitamin D supplementation had stronger benefits for cancer mortality than for cancer incidence.
A secondary analysis of the VITAL trial was done to investigate whether vitamin D supplementation can reduce the risk of developing advanced (defined as metastatic or fatal) cancers . The analysis studied the following endpoints:
There was a significant reduction in the risk of developing advanced cancers in patients taking vitamin D compared to the placebo group. Subgroup analysis also found that similar significant effects were only found in participants with normal BMI and not in those who are overweight or obese.
Laboratory studies have shown that the active form of vitamin D (calcitriol) is involved in multiple cell-signaling pathways, including those responsible for cell division, inflammation, angiogenesis (formation of new blood vessels by the cancer cells) and metastasis (migration of cancer cells) .
Other lab studies also found that vitamin D could induce apoptosis (programmed cell death), suggesting a possible role in affecting cancer outcomes .
Immune Health and COVID-19
Vitamin D has been shown to modulate immune responses, as vitamin D receptors are present on immune cells . Other than being associated with upper respiratory tract infections (URTI)  and autoimmune diseases like inflammatory bowel diseases (IBD) , low levels of vitamin D may increase the risk of COVID-19 infection and severe disease .
Vitamin D increases the absorption of calcium in the gut, which keeps our bones strong . It has been found in several studies that deficiency in vitamin D may lead to loss of bone density. This can result in several diseases such as osteoporosis, rickets (in children), and osteomalacia (in adults) .
Apart from improving bone health, recent studies have suggested that vitamin D also affects other bodily systems and diseases, including cancer, immune health and COVID-19. The VITAL trial and the subsequent secondary analysis have also shown that vitamin D reduces the risk of developing advanced cancer in patients without a diagnosis of cancer at baseline. All these suggest the importance of having sufficient vitamin D supplementation.