Vitamin D Pooling Project
The widespread prevalence of low concentrations of vitamin D has triggered great clinical research and public health interest in determining the amount of vitamin D required for optimal health. Specifically, interest in vitamin D as a cancer preventive agent is related to its biological role in cell signaling and because it is present within most tissues of the body.
The Vitamin D Pooling Project of Rarer Cancers (VDPP) brought together investigators from 10 cohorts to conduct a large prospective epidemiologic study of the association between vitamin D status (measured as serum concentrations of 25-hydroxyvitamin D) and seven rarer cancers: endometrial, esophageal, stomach, ovarian, pancreatic, and kidney cancers, and non-Hodgkin lymphoma. Vitamin D levels in study participants were measured in serum collected before the development of cancer, an advantage in assessing whether vitamin D levels affected cancer susceptibility.
The VDPP is an initiative of the NCI Cohort Consortium, an international collaboration of investigators responsible for more than 40 independently funded population cohorts who partner to conduct a wide range of cancer studies. Eight of the VDPP cohorts are funded by the Epidemiology and Genetics Research Program (EGRP), Division of Cancer Control and Population Sciences (DCCPS), and two of the cohorts are funded by the Division of Cancer Epidemiology and Genetics (DCEG), which is the intramural epidemiology research component of the National Cancer Institute (NCI).
Pooled analyses were conducted to assess potential associations between 25(OH)D and the seven rarer cancers. These analyses incorporated existing relevant case-control data from the participating cohorts. The findings from the VDPP do not support the hypothesis that circulating 25(OH)D concentrations are associated with a reduced risk of developing any of these seven rarer cancers.
- Across each cancer site, there was no evidence of a protective association between higher concentrations of 25(OH)D (>75nmol/L) and cancer outcome.
- For lower levels of 25(OH)D (≤25 nmol/L), investigators did not observe an increased risk for any of the cancer sites.
- An increased risk at very high levels (>100 nmol/L) was noted for pancreatic cancer, similar to some previous reports.
The findings from the VDPP should be examined in other populations. Further research is needed to clarify the biological mechanisms of the possible role for vitamin D in cancer etiology or prevention. NCI is sponsoring a clinical trial, VITamin D and OmegA-3 TriaL (VITAL), that may provide some answers as to how vitamin D supplementation affects total cancer risk and total mortality. However, additional observational studies are needed to identify if any levels of vitamin D may cause harm, especially for rarer cancers. Additionally, independent investigators are continuing to study the associations of vitamin D levels for more common cancers.