Poor survival among African-American cancer patients could be explained by low vitamin D levels
Friday, June 15, 2012. The authors of a review published in the April/May/June 2012 issue of the journal Dermato-Endocrinology suggest that decreased production of vitamin D by African Americans may be a reason for their higher rates of cancer mortality in comparison with Caucasians.
William B. Grant of the Sunlight, Nutrition and Health Research Center in San Francisco and Alan N. Peiris of Mountain Home Veterans Administration Medical Center and East Tennessee State University write that various factors have been suggested to explain African Americans' increased likeliness of dying from a variety of cancers, including cancer stage at time of diagnosis, socioeconomic status and differences in treatment. The incidence of many of these cancers or the risk of dying from them has been associated in numerous studies with reduced sun exposure and/or lower serum 25-hydroxyvitamin D [25(OH)D] levels. Because African Americans have a 40 percent lower serum 25-hydroxyvitamin D concentration than Caucasians due to darker skin pigmentation that impairs production of the vitamin from sunlight, Drs. Grant and Peiris suggest a causative role for insufficient vitamin D levels in the decreased survival observed in this group. The current review evaluates scientific literature concerning cancer disparities between African Americans and Caucasians, as well as studies examining vitamin D status and cancer in order to evaluate the evidence supporting this hypothesis.
Seventeen studies concerning the association between vitamin D adequacy or deficiency and cancer recurrence and survival were included in the review. Significant associations between higher vitamin D levels and cancer survival were found in studies that analyzed all cancers as well as those that evaluated breast, colon, colorectal, lung and prostate cancers, and lymphocytic leukemia/chronic lymphocytic lymphoma, Hodgkin's lymphoma and non-Hodgkin's lymphoma. Also reviewed were 37 studies that examined cancer mortality rate disparities not explained by known factors for 25 types of cancer occurring among African Americans and Caucasians. "Statistically significant disparities emerged for cancer-specific survival rates for 13 types of cancer: bladder, breast, colon, endometrial, lung (non-small cell, stage III, IV), ovarian (advanced), pancreatic, prostate, rectal, testicular, vaginal cancer, Hodgkin lymphoma, stage II, and melanoma," the authors report. "All cancers for which a disparity in cancer-specific survival was reported also have evidence for a beneficial role of vitamin D, as do most of those for which we found disparities for all-cause survival."
Because cancer takes years to reach a stage in which it can be detected, high serum vitamin D concentrations over the course of a lifetime are needed to reduce risk, the authors note. Once the disease has been diagnosed, vitamin D improves survival via antiangiogenic and antimetastatic mechanisms, as well as by other factors. In addition to reduced production of vitamin D by the skin, obesity (which occurs more often among African Americans compared to Caucasians) could also account for some of the lower levels of vitamin D that occur in this population, since having a higher body mass index has been correlated with decreased vitamin D status.
"Lower serum 25(OH)D concentrations among African Americans than white Americans may explain many of the cancer survival disparities after consideration of socioeconomic status, stage at time of diagnosis, and treatment," the authors conclude. "If substantially correct, programs to increase serum 25(OH)D concentrations among African Americans could reduce the cancer disparities."
An article published online on January 25, 2012 in Cancer Epidemiology, Biomarkers and Prevention reports an association between higher prediagnostic levels of vitamin D and increased survival among patients with colorectal cancer.
The study evaluated the association between serum vitamin D levels and mortality among 1,202 men and women enrolled in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort, which recruited over 520,000 participants from 1992 to 1998. Subjects in the current study were diagnosed with colorectal cancer between enrollment and June, 2003. Blood samples obtained upon recruitment were analyzed for serum 25-hydroxyvitamin D [25(OH)D]. Over a mean follow-up period of 73 months, 444 deaths due to colorectal cancer and 97 deaths from other causes occurred.
Men and women whose serum vitamin D levels were among the top 20 percent of participants had a 31 percent lower risk of dying from colorectal cancer and a 33 percent lower risk of mortality from any cause compared to those whose levels were among the lowest 20 percent. Having a high vitamin D level was protective against cancers of both the colon and the rectum. When subjects were analyzed according to calcium intake, a significant protective effect of vitamin D was observed only among those with high dietary calcium.
"If verified in other studies, calcium supplementation in combination with vitamin D may be potentially useful for improved survival in colorectal cancer patients," the authors write. "This large and comprehensive study, based on the EPIC cohort has shown that higher blood vitamin D levels before colorectal cancer diagnosis are associated with reduction in colorectal cancer-specific and overall mortality. Further prognostic studies among cancer patients are needed to determine whether 25(OH)D levels at diagnosis and post-diagnosis correlate with those measured prior to diagnosis, and influence all-cause and disease-specific survival among colorectal cancer patients."
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