By Nathan Seppa, Science News
NEW ORLEANS—A shortage of vitamin D may stack the deck against people fighting a common form of lymphoma, researchers reported December 5 at a meeting of the American Society of Hematology. The new study adds this cancer to the list of malignancies suspected of being more difficult to control in patients with vitamin D deficiency common in parts of the U.S. population.
From 2002 to 2008, the researchers analyzed blood samples from 374 newly diagnosed patients with diffuse large B-cell lymphoma, a fast-growing cancer of white blood cells called B cells. It mainly hits people over 50 and accounts for roughly 40 percent of lymphomas.
The study participants averaged 62 years of age. The blood tests revealed that half were deficient in vitamin D at the start of treatment, having less than 25 nanograms per milliliter of blood.
The scientists monitored the patients for an average of three years. During the follow-up, patients who were deficient in vitamin D were twice as likely to die, compared with patients who had adequate vitamin D blood levels at the outset. Patients with low vitamin D concentrations were also about 50 percent more likely than the others to have their cancer worsen, says endocrinologist Matthew Drake of the Mayo Clinic in Rochester, Minn., who presented the findings.
All patients received standard treatment, including chemotherapy, and the researchers accounted for differences between groups in age and other factors that might bias the comparison.
Vitamin D facilitates calcium absorption in the body, an essential function. While the minimum healthy blood levels of vitamin D are a matter of debate, many scientists draw the line at 25 or 30 ng/ml. Others suggest we need more vitamin D and suggest the minimum healthy level should be defined as 40 ng/ml. “I think right now it’s a moving target,” Drake says. He and his colleagues chose 25 ng/ml because that is the point at which the body starts leaching calcium from bone to maintain appropriate blood levels of calcium.
Drake says more study is needed before supplementation of vitamin D should be ordered for lymphoma patients. Part of his hesitation stems from the lack of clarity surrounding the link between cancer and a vitamin D deficiency.
Past evidence has shown that the vitamin can promote gene regulation, programmed cell death when necessary, and other critical cell functions. “Whether or not vitamin D deficiency plays a role in lymphoma, we really can’t say at this point,’ he says.
But vitamin D deficiency has been linked to cancers in past studies. Maps suggest that mortality rates from cancer are higher in the northernmost areas of the United States — notable because less sun exposure means less vitamin D production — and some studies have linked vitamin D deficiency with a worse outcome in people with cancer of the breast, colon and throat.
The link between a vitamin D deficiency and a worse outcome for this cancer is plausible, says Ola Linden, a medical oncologist at Lund University in Sweden. But the finding might still be influenced by genetic differences among the patients and other factors, and needs to be validated in a trial in which patients are randomly assigned to get vitamin D supplements or not, he says. If the results from such a test were similar to these, he says, oncologists would have another weapon with which to fight this cancer — free of charge.
Although fortified foods provide some vitamin D, these may be inadequate to maintain ideal health levels. While the recommended daily dose of vitamin D, currently set at 400 IUs, stops rickets, many scientists suggest that three times that amount would be useful and wouldn’t risk an overdose.
Vitamin D can be obtained in food or manufactured in the skin by exposure to ultraviolet B radiation from the sun. The vitamin can be stored, but during winter months in temperate zones the supply dwindles. For bone health, Drake recommends that people in the Upper Midwest take vitamin D supplements during winter months and get an hour to an hour and a half of sun exposure each week in the summer. “We’ve become a society where we spend the vast majority of our time indoors,” he says. “It’s very hard to find what I call ‘free-range humans.’”