A large prospective study has found that levels of vitamin D circulating in the bloodstream are not associated with subsequent risk of developing seven rare cancers, including endometrial, esophageal, stomach, ovarian, pancreatic, and kidney cancers and non-Hodgkin lymphoma. Although each of these cancers is individually uncommon, they collectively account for about a quarter of all deaths from cancer in the United States. The results were reported in a series of studies published online in the American Journal of Epidemiology on June 18.

“These cancer sites were chosen because there was a paucity of previous epidemiological studies, though basic research and biological evidence had suggested vitamin D may play a role in altering risk for these cancers,” said Dr. Demetrius Albanes of NCI’s Division of Cancer Epidemiology and Genetics. “Because these cancers are relatively rare, no one study could address risk; by pooling data from 10 studies, we had greater power to rigorously test the vitamin D hypothesis for these cancer outcomes.”

The researchers, part of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers, measured blood concentrations of 25-hydroxy vitamin D, which is the primary form of this vitamin circulating in the bloodstream. Lower cancer risk was not observed in persons with high vitamin D blood concentrations compared with normal concentrations for any of these cancers. At the other end of the spectrum, higher cancer risk was not seen in participants with low vitamin D concentrations. However, researchers did observe an increased risk of pancreatic cancer for a small number of patients (2.3 percent) with very high blood concentrations of vitamin D (100 nmol/L or greater). “This finding needs to be followed up in further studies,” said Dr. Albanes.

Dr. Kathy J. Helzlsouer of the Prevention and Research Center at Mercy Medical Center in Baltimore, MD, who served as the chair of the project’s steering committee, wrote in the overview of the importance of optimum concentrations of vitamin D, particularly for bone health. A message of the study, she suggested, was “all things in moderation. You don’t want vitamin D levels that are too low, and you don’t want levels that are too high.”

“These studies offer compelling evidence against the hypothesis that circulating levels of vitamin D are relevant to risk of these cancers,” wrote Dr. Tim Byers of the University of Colorado Cancer Center, Aurora, in an accompanying editorial. This new information is important, he continued, because a review by the International Agency for Research on Cancer had decided that evidence was previously insufficient to draw conclusions about these cancer sites.

source: NCI bulletin