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A study by an international group of researchers from organizations including the American Cancer Society finds that higher levels of vitamin D in the blood is associated with a lower risk for getting colorectal cancer. Previous studies have suggested a link but were inconclusive. The new study was published online June 14, 2018 in the Journal of the National Cancer Institute.
The researchers combined data from 17 prospective studies, which is a type of study that follows people over time to try to determine why some of them get a certain disease, in this case colorectal cancer. The analysis is the largest to date, using data from about 12,800 people. All participants were tested for vitamin D levels in their blood before diagnosis. Often, this measure was taken when they initially joined the study. They became part of the new analysis because they developed colorectal cancer. Another group was matched to the study group by age, race and date of blood draw. These “matched” controls were people who did not have colorectal cancer. All the blood was tested or re-tested using the same method at the same medical laboratory for consistency.
Vitamin D has long been known to be needed for bone health. Participants in the study were considered to have enough levels of vitamin D in their blood if they met the National Academy of Medicine (NAM) suggested levels of circulating vitamin D based on evidence for maintaining healthy bones.
The study found that people with deficient serum vitamin D levels according to the NAM definition had a 31% higher risk of colorectal cancer during the length of time they were followed, which was an average of 5 ½ years (the full range was 1-25 years). The lowest colorectal cancer risk was found in people who had circulating vitamin D levels even higher than the NAM recommendation for sufficient concentrations. However, the risk did not continue to decrease for the very highest levels of vitamin D concentrations the study looked at.
According to Marji McCullough, ScD, RD, American Cancer Society epidemiologist and co-first author of the study, the findings indicate there may be a target range of circulating vitamin D levels that may be associated with lowest risk for colorectal cancer. She said, “What’s optimal for colorectal cancer may be different for what’s optimal for bone health.” In the US, laboratories often use different methods when measuring vitamin D status than were used in this study, and may have different definitions from NAM of how much is needed to be healthy.
However, these findings do not change current public health policy. “This large study can contribute to the evidence that is reviewed by scientific committees that determine nutrient recommendations,” said McCullough.
People can get vitamin D from their diet, from supplements, and from the sun. However, staying out in the sun without protection exposes people to harmful UV rays, which is a strong risk factor for skin cancer. And getting too much vitamin D, for example, from taking very high doses of supplements, can be harmful. McCullough offers these tips:
McCullough points out there is already strong evidence that several important ways to lower the risk for colorectal cancer are to adopt certain lifestyle habits. They include:
Adopting healthy lifestyle habits can also lower your risk for other diseases including heart disease and type 2 diabetes.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts. Published June 14, 2018 in the Journal of the National Cancer Institute. First author Marjorie L. McCullough, ScD, RD, American Cancer Society, Atlanta, Ga.
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