For many years, scientists have tried to explain disparity in cancer survival rates between white Americans and African Americans. Possible explanations have included factors such as cancer stage at time of diagnosis, socioeconomic status and differences in treatment. But recently, scientists have turned their attention to the role of vitamin D, or specifically, lower levels of the vitamin and its association with a poorer prognosis.
In a recent review* 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 looked at 17 different studies concerning the association between vitamin D adequacy or deficiency and cancer recurrence and survival. The researchers found significant associations between higher vitamin D levels and cancer survival 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.
They also reviewed 37 studies that examined cancer mortality rate disparities that could not be explained by known factors for 25 types of cancer occurring among African Americans and Caucasian-Americans. They found statistically-significant disparities in 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 researchers report that all cancers for which a disparity in cancer-specific survival was reported also show evidence that vitamin D plays a beneficial role in survival.
So why do African Americans have lower vitamin D levels? It has to do with darker pigmentation impairing the production of vitamin D from sunlight. Because the body produces vitamin D from sun exposure and because the darker pigmentation impairs production of the vitamin from sunlight, African-Americans will naturally produce less of it.
Drs. Grant and Peiris believe that the results of their review suggest that if their conclusions are correct, programs to increase serum vitamin D concentrations among African Americans could reduce the cancer disparities.