A study by at Wake Forest Baptist Medical Center in Winston-Salem N.C., Keck School of Medicine at the University of Southern California (USC) and the Cancer Prevention Institute of California suggests that a high intake of calcium causes prostate cancer among African-American men who are genetically good absorbers of the mineral.
According to Gary G. Schwartz, Ph.D., associate professor of cancer biology, urology, and public health sciences at Wake Forest Baptist and co-author on the study “High dietary intake of calcium has long been linked to prostate cancer but the explanation for this observation has been elusive. The researchers looked at 783 African-American men living in the San Francisco and Los Angeles areas, 533 of whom were diagnosed with prostate cancer. They studied the effects of genotype, calcium intake and diet-gene interactions.
This study is one of the few to date to explore genes related to calcium absorption or to examine diet in a large African-American population. Prostate cancer is 36 percent more common among African-Americans than in non-Hispanic whites, data on the diet-cancer link primarily comes from Caucasian populations. The researchers targeted a genetic allele which is associated with regulating the absorption of calcium and that is more common in men of African origin than in other populations.
The study, published in the online issue of the Journal of Bone and Mineral Research, found that
1- Men who reported the highest intake of calcium were two times more likely to have localized and advanced prostate cancer than those who reported the lowest.
2- Men with a genotype associated with poor calcium absorption were 59 percent less likely to have been diagnosed with advanced prostate cancer than men who genetically were the best absorbers of calcium.
3- Among men with calcium intake below the median, genetically poor absorbers had a 50 percent decreased risk of having advanced prostate cancer than the best absorbers. The final paper is scheduled to appear in the January 2012 print issue.
Sue Ann Ingles, Dr.P.H., Associate Professor of Preventive Medicine at USC and a principal investigator of the study said this poses a “conundrum”. She said that calcium appears to increase risk for prostate cancer, it is essential for bone health and appears to protect against colorectal cancer.
This study needs to confirm that the genetic conclusions are actually the result of the allele rather than the possibility that they were simply studying an allele that is highly associated with African-American men (correlation vs. causation).
Unlike age and race, which are fixed risk factors for prostate cancer, diet is modifiable. So, it might be possible for men having a definable genetic predisposition to prostate cancer to modify their diet to limit their risk factors of developing prostate cancer. If a person is a good absorber of calcium dietary modifications could limit the risk of developing prostate and advanced prostate cancers.
The study was funded by grants from the National Institute of Environmental Health Sciences, The Cancer Research Fund of the California Department of Health Services Cancer Research Program and the National Cancer Institute. Co-authors on the paper, in addition to Schwartz and Ingles, include: Glovioell W. Rowland, from USC; and Esther M. John, from the Cancer Prevention Institute and the Department of Health Research and Policy at Stanford University School of Medicine and Stanford Cancer Center.
Joel T Nowak, M.A., M.S.W.