WASHINGTON—Higher levels of vitamin D do not protect against certain cancers, including non-Hodgkin lymphoma or cancer of the endometrium, esophagus, stomach, kidney, ovary or pancreas, according to a new study from the National Cancer Institute (NCI).
As part of a collaborative effort of the NCI Cohort Consortium, investigators from the Vitamin D Pooling Project of Rarer Cancers examined vitamin D levels in blood that had been collected from more than 12,000 men and women participating in one of the studies. Some of those individuals went on to develop cancer. Vitamin D concentrations were measured using 25-hydroxyvitamin D (25(OH)D), which is the major form of this vitamin in the bloodstream.
Participants were followed for the development of cancer for up to 33 years, depending on the study. Investigators then compared cancer rates in participants whose levels of vitamin D in stored blood were high (above 75 nmol/L, or nanomoles per liter) or low (less than 25 nmol/L) with rates in participants whose levels of vitamin D were within the normal range (50 to 75 nmol/L).
For the small number of participants with vitamin D levels greater than 100 nmol/L, investigators observed elevated risk of pancreatic cancer, but not for the other cancers in these studies. They recommended further research to clarify this relationship.
Through the Vitamin D Pooling Project, researchers had access to a geographically and demographically diverse group of men and women, including participants from the United States, Finland, and China. In this collection of groups of study participants, the proportion of the study population that was deficient in vitamin D varied from 3 percent to 36 percent, depending on geographical latitude, season during which the blood was collected, race, and other factors. The investigators had a wealth of other information on participants, including smoking history, lifestyle and diet. As in other studies, individuals with higher 25(OH)D levels were more likely to be male, lean and physically active. Those with higher levels also reported greater intake of multivitamins, calcium supplements, and foods rich in vitamin D.
"In this pooled analysis of cohort data, vitamin D was not associated with lower risk for these less common cancers, despite well-established benefits for bone health," the researchers concluded.