BOSTON, Mass. — Scientists have suspected for decades that vitamin D helps prevent cancer to some extent, but have struggled to come to any conclusive findings. Now, a new study finds vitamin D drops the risk of developing advanced cancers by 17 percent.
Prior studies had revealed people living closer to the equator (and thus receiving more sunlight and vitamin D) experience lower than average rates of certain cancers. Similarly, experiments performed on mice show that vitamin D can indeed slow the progression of cancer to a certain extent. However, randomized clinical trials focusing on vitamin D and cancer have ultimately produced confusing results. The Vitamin D and Omega-3 Trial (VITAL) in 2018 declared vitamin D does not reduce the overall incidence of cancer. It did however find some evidence suggesting vitamin D can decrease risk of death by cancer.
Weight plays important role in how vitamin D lowers cancer risk
These new findings are actually the result of a secondary analysis of VITAL. Researchers at Brigham and Women’s Hospital focused more specifically on the relationship between vitamin D supplements and metastatic/fatal cancer risk. Besides the overall 17 percent drop in advanced cancer risk, when researchers only examined participants with a normal Body Mass Index (BMI), they noted an astounding 38-percent drop in advanced cancer likelihood in patients taking regular vitamin D supplements.
“These findings suggest that vitamin D may reduce the risk of developing advanced cancers,” says epidemiologist and corresponding author Paulette Chandler, MD, MPH in a media release. “Vitamin D is a supplement that’s readily available, cheap and has been used and studied for decades. Our findings, especially the strong risk reduction seen in individuals with normal weight, provide new information about the relationship between vitamin D and advanced cancer.”
The original VITAL study was a placebo-controlled project that took place over the course of five years. The participants included men over 50 years-old and women over 55 who showed no signs of cancer at the start. The VITAL study’s original goal was to investigate the different effects of vitamin D and omega-3 supplements on cancer rates. Researchers separated the more than 25,000 participants into four groups.
One group took vitamin D (2000 IU/day) plus omega-3s; another took vitamin D plus placebo on a daily basis; the third group received omega-3s and a placebo; and the last group only took placebos. The first time around, researchers didn’t note any statistical difference among the four groups regarding cancer rates, but a drop in cancer-related deaths did emerge.
A second look reveals key cancer clues
In the second analysis, researchers focused solely on advanced (metastatic or fatal) cancer rates among VITAL participants. These patients either did or did not take vitamin D during the original study.
Close to 13,000 participants had taken vitamin D during the VITAL study. Among that group, 226 eventually developed an advanced form of cancer. In comparison, 274 people taking placebos developed advanced cancer. Regarding lower BMI, 7,843 people with a normal BMI took vitamin D supplements, with 58 of those subjects eventually being diagnosed with advanced cancer. Meanwhile, 96 people with a normal BMI taking placebos developed advanced cancer.
Why does BMI apparently influence vitamin D’s cancer benefits? Study authors say there is evidence that both obesity and inflammation render vitamin D less effective, either by hurting vitamin D receptor sensitivity or changing vitamin D signaling.
“Our findings, along with results from previous studies, support the ongoing evaluation of vitamin D supplementation for preventing metastatic cancer — a connection that is biologically plausible,” Chandler concludes. “Additional studies focusing on cancer patients and investigating the role of BMI are warranted.”
The study is published in JAMA Network Open.