Among African American men with abnormal prostate-specific antigen levels or abnormal findings on digital rectal examination of the prostate, biopsies are more likely to detect prostate cancer in those who have vitamin D deficiency than in those who don’t, according to a report published online May 1 in Clinical Cancer Research.
And in both American men of European descent and African American men who have vitamin D deficiency, initial biopsies are more likely to show tumors with high Gleason grade and more advanced clinical stage than are tumor biopsies in men who don’t have vitamin D deficiency, reported Dr. Adam B. Murphy of Northwestern University, Chicago, and his coauthors.
Their "novel" findings corroborate "a plethora of in vitro, animal, and clinical data suggesting potential mechanisms for the role of vitamin D in prostate differentiation and tumor progression," the investigators noted.
If vitamin D is involved in prostate cancer initiation or progression, then vitamin D supplements may prove helpful for both primary and secondary prevention, especially in the highest-risk group of African American men, Dr. Murphy and his colleagues said.
The researchers investigated this issue because no prior studies have assessed the association between vitamin D status and prostate biopsy outcomes, even though several have suggested that vitamin D deficiency might explain the disparity between blacks and whites in prostate cancer incidence and survival. "African American men have lower serum vitamin D levels than their European American and Hispanic counterparts, in part due to lower skin synthesis from the ultraviolet-blocking effects of melanin in the skin," Dr. Murphy and his associates said.
They examined these outcomes in an ethnically diverse population of 667 men residing in Chicago, a city with low ultraviolet light exposure. There were 275 European Americans, 273 African Americans, and 119 men of other ethnicities.
The study participants, aged 40-79 years, were enrolled over a 4-year period from five urology clinics. They were undergoing an initial biopsy because of elevated prostate-specific antigen levels and/or abnormal findings on digital rectal exam. Vitamin D status was determined using serum samples collected on the day of biopsy.
Vitamin D deficiency (a 25-hydroxyvitamin D level less than 20 ng/mL) was quite common, affecting 41% of the entire study population. Severe vitamin D deficiency (a 25[OH]D level less than 12 ng/mL) was relatively common, affecting 16%.
Prostate cancer was detected in 383 biopsies.
Vitamin D deficiency was not associated with a biopsy finding of prostate cancer among European American men, but it was strongly associated with a biopsy finding of prostate cancer among African Americans (odds ratio, 2.43). This association remained robust when the data were controlled for patient age, prostate-specific antigen level, family history, and cigarette and alcohol use.
In addition, severe vitamin D deficiency was associated with a higher Gleason score and higher tumor stage in both races, and thus with a higher risk category by National Comprehensive Cancer Network criteria (Clin. Cancer Res. 2014;20:2289-99).
"Our work supports the hypothesis that 25-hydroxyvitamin D is a potential biomarker that plays a clinically significant role in prostate cancer, and it may be a useful modifiable risk factor in the disease. Additionally, differences in 25-hydroxyvitamin D levels may explain ethnic disparities in prostate cancer–specific incidence, morbidity, and mortality," Dr. Murphy and his associates wrote.
This study was supported in part by grants from the National Institutes of Health and the U.S. Department of Defense. Dr. Murphy reported no financial conflicts of interest; one of his coauthors reported ties to Beckman Coulter, DeCode Genetics, and Ohmx.