For many years, investigators have been trying to pin down the connection between vitamin D and cancer.
Observational studies have found that people who live near the equator, where exposure to sunlight produces more vitamin D in the skin, have lower incidence and death rates from certain cancers. In cancer cells in the lab and in mouse models, vitamin D has also been found to slow cancer progression.
But the results of randomized clinical trials, the gold standard of scientific evidence, in people haven't yielded a clear answer.
The Vitamin D and Omega-3 Trial (VITAL), which concluded in 2018, found that vitamin D did not reduce overall incidence of cancer, but hinted at a decreased risk of cancer deaths.
Now, a secondary analysis of VITAL, a team led by investigators at Brigham and Women's Hospital has narrowed in on the connection between taking vitamin D supplements and risk of metastatic or fatal cancer.
The researchers found that vitamin D supplementation was associated with an overall 17 percent risk reduction for advanced cancer. When the team looked at only participants with a healthy body mass index (BMI), they found a 38 percent risk reduction, suggesting that body weight may influence the relationship between vitamin D and decreased risk of advanced cancer.
The findings suggest that vitamin D may reduce the risk of developing advanced cancers. The new findings, especially the strong risk reduction seen in people with normal weight, provide new information about the relationship between vitamin D and advanced cancer.
About the VITAL trial
The VITAL study was a rigorous, randomized controlled study that took place over a span of more than five years. Participants included men who were 50 or older and women 55 or older who did not have cancer when the trial began. The study population was racially and ethnically diverse.
The VITAL trial was designed to test the independent effects of vitamin D and omega-3 supplements on health outcomes, as well as the synergy between the two.
Participants were divided into four groups: vitamin D (2000 IU/day) + omega-3s; vitamin D + placebo; omega-3s + placebo; and placebos for both.
Primary endpoints were major adverse cardiovascular events and incidence of cancer. VITAL did not find a statistical difference in overall cancer rates, but researchers did observe a reduction in cancer-related deaths.
The new VITAL analysis
In their secondary analysis, the research team followed up on the possible reduction in cancer deaths with an evaluation of advanced (metastatic or fatal) cancer among participants who did or did not take vitamin D supplements during the trial. They also examined the possible modifying effect of body weight.
Among the more than 25,000 participants in the VITAL study, 1,617 were diagnosed with invasive cancer over the next five years. This included a mix of cancers, including breast, prostate, colorectal, lung and more.
Of the almost 13,000 participants who received vitamin D, 226 were diagnosed with advanced cancer compared to 274 who received the placebo. Of the 7,843 participants with a normal body mass index (BMI less than 25) taking vitamin D, only 58 were diagnosed with advanced cancer compared with 96 taking the placebo.
While the findings on BMI could be due to chance, there is previous evidence that body mass may affect vitamin D action. Obesity and associated inflammation may decrease the effectiveness of vitamin D, possibly by reducing vitamin D receptor sensitivity or altering vitamin D signaling.
In addition, randomized trials of vitamin D and type 2 diabetes have found greater benefits of vitamin D in people with normal weights and no benefit among those with obesity.
Vitamin D deficiency is common among cancer patients, with one study reporting rates of vitamin D deficiency as high as 72 percent among cancer patients. There is also evidence that higher amounts of body fat are associated with increased risk for several cancers.
The findings, along with results from previous studies, support the ongoing investigation of vitamin D supplementation for preventing metastatic cancer, a connection that makes biological sense. Additional studies focusing on cancer patients and investigating the role of body weight are needed.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.