Taking a vitamin D3 supplement reduces a person's risk for metastatic cancer and death by 17%, according to a study published Wednesday by JAMA Network Open.
However, the vitamin supplement does not help lower the risk for developing the disease, the researchers said.
The benefits of vitamin D3 in limiting metastases -- or disease spread to other organs -- and severity was seen across all cancers, and was particularly prominent among study participants who maintained a healthy weight, researchers said.
"The primary message [of our study] is that vitamin D may reduce the chance of developing metastatic or fatal cancer among adults without a diagnosis of cancer," study co-author Dr. Paulette Chandler told UPI.
"Our study [also] highlights that obesity may confer resistance to vitamin D effects," said Chandler, an assistant professor of medicine at Brigham and Women's Hospital in Boston.
The research conducted by Chandler and her colleagues is a follow-up to the ongoing Vital Study.
The study is assessing whether taking daily dietary supplements of vitamin D3 -- at a dose of 2,000 International Units -- reduces the risk for developing cancer, heart disease, and stroke in people who do not have a prior history of these illnesses.
The study population includes nearly 26,000 people, roughly half of whom are taking vitamin D3 supplements daily, while the other half were given a placebo, the researchers said.
Over an average of approximately five years, about 6% of participants in both the vitamin D and placebo groups developed cancer, with cancers of the prostate, breast, and lung being the most common, the data showed.
However, 1.7% of the participants in the vitamin D group developed metastatic disease or died, compared to 2.1% in the placebo group, the researchers said.
In addition, taking vitamin D3 combined with maintaining a healthy weight reduced the risk for metastatic cancer and death by about 40%, according to the researchers.
"Our study evaluated the effect of vitamin D supplementation in individuals that were free of cancer," Chandler said.
"Additional vitamin D supplementation studies focusing on cancer patients and investigating the role of [body weight] are warranted," she said.
Recent research on vitamin D suggests that being deficient in the nutrient -- which up to 60% of adults are -- increases a person's risk for severe illness from COVID-19.
None of the participants who took the supplement in the VITAL study were, according to the researchers.
Although vitamin D is believed to boost immune system health, a recent study found that taking a supplement did not reduce the risk for infection in older adults.