Vitamin D plays a role in the prevention of colon cancer in people who've never had the disease and may also boost the survival of those already diagnosed with the malignancy, researchers have found in separate investigations.
The analyses, conducted by scientists at the Dana-Farber Cancer Institute in Boston, found that the vitamin is intimately involved with immune system function.
"We have known for a while that vitamin D may play a role in the prevention of other forms of cancer," said Dr. Robert Graham, an internist in the Office of Community and Public Health with the North Shore-Long Island Jewish Health System.
Graham, who was not involved in the Dana-Farber research, added that there are vitamin D receptors on "all of our cells" and that earlier studies have suggested a link between vitamin D intake and lower breast cancer risk.
The new research, published in the current issue of the journal Gut, marks the first association between vitamin D and an immune response to cancer in a large human population, Dana-Farber scientists said.
Dr. Shuji Ogino of Dana-Farber and the Harvard School of Public Health, said he and his team culled their data from databases involving 170,000 participants in the Nurses' Health Study and the Health Professionals Follow-up Study. Both are long-term health-tracking research projects.
Ogino compared 318 colorectal cancer patients and 624 individuals who never developed the disease. All of them had blood samples drawn in the 1990s, before the 318 developed cancer.
Investigators recently tested the preserved samples for 25-hydroxyvitamin D, a compound produced by the liver from the vitamin, and found that patients with high levels had a lower-than-average risk of developing colorectal tumors. These samples also had high levels of immune-system cells, the team found.
Colorectal cancer is the third most common malignancy diagnosed in both men and women in the United States, according to the American Cancer Society. The society estimates 49,700 deaths in 2015.
"Vitamin D boosts immune system function by activating T cells," Ogino said of the key disease-fighting components of the immune system.
Ogino's study comes on the heels of another Dana-Farber study presented earlier this week in San Francisco at a meeting of the American Society of Clinical Oncology.
Dr. Kimmie Ng reported that patients whose colorectal cancer had already spread survived longer if they had high levels of vitamin D in their bloodstream before chemotherapy and treatment with targeted cancer drugs.
In Ng's investigation, patients with the highest blood levels of vitamin D survived a median period of 32.6 months, compared with 24.5 months for those with the lowest levels.
Graham, who is also director of integrative health at Lenox Hill Hospital in Manhattan, applauded both investigations but said he's dismayed because the U.S. Preventive Services Task Force, a panel of national experts in preventive medicine, voted against routine screening for vitamin D levels.
The task force concluded in November that data was so scant, members could not recommend that primary care doctors test patients for vitamin D levels.
"I recommend that patients take anywhere from 800 to 1,000 international units a day," Graham said, referring to vitamin D supplements. Vitamin D is also produced by the body in response to sunlight exposure.