Deep Dive: Does supplementing the sunshine vitamin impact colorectal cancer outcomes?

Colorectal cancer affects up to 1.8 million^[1] people each year and it is responsible for roughly 850,000 deaths^[1] worldwide. There appears to be at least some environmental components^[2] to colorectal cancers, as there are major differences in incidence rates based on geographical locations and socioeconomic strata. One hypothesis for the substantial differences in incidence rates is that vitamin D may play a role in the development and progress of several cancers, including colorectal cancers.

There is data linking vitamin D to colorectal cancer. For example, an observational study found that there is an inverse correlation^[3] between colorectal cancer incidence rates and sunlight exposure by geographical location. Mechanistically, cultured colon cancer cells^[4] divide at a slower rate when treated with vitamin D, compared to when they’re untreated. However, not all research has produced supporting evidence. For example, a Mendelian randomization study did^[5] not show a clear causal impact of blood 25-hydroxyvitamin D level on CRC risk. Furthermore, several studies have reported that supplementation with vitamin D does not reduce the risk of developing cancer^[6], including colorectal cancer^[7]. In addition to prevention, there have been several randomized trials examining the effect of vitamin D supplementation on the progression of already established colorectal cancer. The present study was systematic review and meta-analysis of randomized controlled trials examining the effect of vitamin D supplementation not on incidence of colorectal cancer, but on the survival and progression of disease in participants who had already developed it.

Vitamin D has been linked to colorectal cancer through observational and mechanistic research. Recently, several randomized trials have investigated the role of vitamin D supplementation on slowing disease progression and improving survival among people with colorectal cancer. The present study was a systematic review and meta-analysis of randomized controlled trials examining the effect of vitamin D supplementation on disease progression and survival among people with colorectal cancer.