Colorectal Cancer and Vitamin D
Patients receiving chemotherapy for colorectal cancer are likely to have severe vitamin D deficiency and may need high-dose vitamin D supplements to bring their levels up to normal, according to a study published online October 2 in the International Journal of Colorectal Disease.
Vitamin D has an important link to colorectal cancer. A number of studies have found an association between vitamin D deficiency and an increased risk of colorectal cancer, as well as a worse prognosis in people who have the disease. “We know there’s an association between vitamin D levels and increased risk of adenomas (tumors), as well as an increased risk of colon cancer,” says lead study author Marwan G. Fakih, associate professor of Oncology at the Roswell Park Cancer Institute in Buffalo, New York. “And at least two studies have linked improved outcome with higher levels of vitamin D.”
People get vitamin D from dietary sources (such as milk), as well as from being outside (vitamin D is produced in sun-exposed skin). Although researchers are not exactly clear how vitamin D might protect against cancer, they believe that it reduces cancer cells’ ability to grow and enhances cellular differentiation, Dr. Fakih says.
He and his colleagues looked at vitamin D status in 315 colorectal cancer patients, half of whom had been receiving chemotherapy. Patients in the chemotherapy group were about three times more likely to have very low vitamin D levels (15 nanograms per milliliter (ng/ml) or less) than patients who weren’t receiving chemotherapy. Only about a quarter of the chemotherapy patients in the study had vitamin D levels within the recommended range of 32 to 100 ng/ml.
The authors say this deficiency may occur because chemotherapy patients are less likely to get outside in the sunlight, or they may limit vitamin D-fortified milk products in their diet to prevent chemotherapy-induced diarrhea. It’s also possible that chemotherapy might affect the body’s ability to absorb vitamin D or use it in its active form.
Dr. Fakih cautions that the association between low vitamin D levels and cancer risk does not necessarily mean that vitamin D deficiency causes colon cancer or shortens the lifespan of those with the disease. “True, we see low levels of vitamin D, but that does not mean that if you replace it these patients will do better,” he says. He and his colleagues are currently studying how well colorectal cancer patients on chemotherapy respond to a daily 2,000 IU vitamin D supplement.
For now, Dr. Fakih believes chemotherapy patients should have their vitamin D levels regularly tested—a practice that is not common in the United States. “The reason we test them is that there really is not a whole lot to lose here,” he says. “Replacing vitamin D in patients with vitamin D deficiency may also have positive effects on bone health, as well as on the cardiovascular and immune systems.”
How well vitamin D supplements might protect healthy people against colorectal cancer is still uncertain, because this and other studies have focused specifically on patients who already have colorectal cancer. More research is needed to determine the benefit—and optimal dose—of vitamin D for cancer prevention, Dr. Fakih says.