A secondary review of the Critical randomized clinical trial concluded that overall, a 17 percent decrease in the risk of metastatic or fatal cancer and a 38 percent decrease in the risk of people with normal BMI were observed.
Medical researchers have speculated the link between vitamin D and cancer for several years.
Epidemiological research has shown that people who live at higher latitudes have a lower chance of contracting such cancers.
In cancer cells and in mouse models, vitamin D has also been shown to delay the progression of cancer development.
Despite promising outcomes in animal studies, however, the results in human clinical trials have been less definitive.
The Vitamin D and Omega-3 Trial (VITAL), completed in 2018, showed that vitamin D had no effect on cancer incidence, but was associated with a decreased risk of death from cancer. Nevertheless, findings from a secondary review of the Critical study indicated that supplementary vitamin D use was associated with a decreased risk of metastatic or fatal cancer.
A research recently reported in JAMA Network Open records an overall 17% reduction in the risk of cancer with vitamin D supplements.
When testing only participants with normal BMI, the team found a 38% reduction in risk, indicating that body mass could influence the relationship between vitamin D and reduced risk of cancer.
“These results suggest that vitamin D may reduce the risk of developing advanced cancers,” said corresponding author Paulette Chandler, MD, MPH, a family physician and epidemiologist in Brigham’s Division of Preventive Medicine. “Vitamin D is a supplement that is readily available, cheap, and has been used and studied for decades. Our results, particularly the large risk reduction in people of normal weight, provide new information about the link between vitamin D and advanced cancer.”
The Critical experiment was a systematic, placebo-controlled study requiring more than five years of follow-up.
The research population included men and women in the ages of 50 and older, and who did not have cancer at the start of the study.
The sample of the students is culturally and ethnically diverse. The Critical research was planned to determine the effectiveness of vitamins D and omega-3 supplements, and whether or not the two function synergistically. Members of four classes were given either vitamin D and omega-3 fatty acids, vitamin D, omega-3 fatty acids and placebos, and placebos in that order. The primary endpoints were mainly for severe cardiovascular events and disease incidence. VITAL found no statistical difference in total death rates, but noted a decline in death rates of individuals dying from cancer.
In their second review, Chandler and colleagues monitored the possible reduction in cancer deaths with an assessment of advanced (fatal or metastatic) cancers among participants who did or did not take vitamin D supplements during the research.
They also tested the effects of BMI, overall.
1,617 people were diagnosed over the next five years with invasive cancer over those five years.
The cancers contained several different kind of cancer (breast, prostate, colorectal, lung and more). For those taking the vitamin D, there were 226 who were diagnosed with advanced cancer, as opposed to 274 who took the placebo. Among the 7,843 participants with a typical BMI (less than 25) who took vitamin D, 58 were diagnosed with cancer, while among the placebo group of 626, 96 were diagnosed with cancer.
Although the team’s results on BMI may have been by chance, there are prior studies that have shown that the level of body mass can affect the effects of vitamin D. Overweight and osteoarthritis (OA) can reduce the effectiveness of vitamin D, likely by impairing vitamin D signaling or decreasing the sensitivity of the vitamin D receptor.
In addition, randomized trials have shown that vitamin D does not promote benefit in people with average weight, but does promote benefit in people with obesity.
Vitamin D deficiency is prevalent in cancer patients. One research found vitamin D deficiency rate as high as 72 percent in children with chronic illness.