Taking vitamin D supplements may reduce the overall risk of developing advanced cancer by 17%, a study suggests.
The researchers also report that the risk of metastatic (cancer which has spread to a different part of the body) or fatal cancers is even lower for those who have a healthy weight and are consuming vitamin D.
The results, published in the journal Jama Network Open, are based on the Vitamin D and Omega-3 Trial (Vital), which concluded in 2018.
Back then, scientists found that vitamin D did not reduce overall incidence of cancer but there was a decreased risk of cancer deaths.
But a secondary analysis led by Brigham And Women’s Hospital in Boston, Massachusetts, US, suggests vitamin D is associated with a 17% risk reduction for advanced cancer overall and a 38% reduction among those with normal body mass index (BMI).
Dr Paulette Chandler, a primary care physician and epidemiologist in the Brigham And Women’s Hospital, and one of the authors on the study, said: “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.”
More than 25,000 people took part in the Vital study, which spanned more than five years.
The participants included men aged 50 or above and women 55 or older who did not have cancer when the trial began.
The test subjects were divided into four groups – the first group took a daily dose of vitamin D (2,000 IU/day) along with omega-3s; the second group took vitamin D plus a placebo (a substance designed to have no therapeutic value); the third consumed omega-3s plus placebo, while the fourth group only had placebos.
The initial results showed no statistical difference in overall cancer rates but a reduction in cancer-related deaths was observed.
In their secondary analysis, Dr Chandler and colleagues evaluated the risk of developing advanced cancer among participants who did or did not take vitamin D supplements during the trial.
They also examined whether an individual’s BMI played a role.
Among the participants, 1,617 were diagnosed with an invasive form of cancer – such as breast, prostate, colorectal, lung – over the next five years.
Among those who received vitamin D, 226 were diagnosed with advanced cancer, compared to 274 who received the placebo.
Of those with a normal BMI (less than 25) taking vitamin D, 58 people were diagnosed with advanced cancer compared with 96 taking the placebo.
The team said they found no association between omega-3 fatty acid supplementation and advanced cancer.
The researchers believe obesity and associated inflammation may decrease the effectiveness of vitamin D.
Dr Chandler said: “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.
“Additional studies focusing on cancer patients and investigating the role of BMI are warranted.”