Despite many studies that report black patients infected with chronic hepatitis C virus genotype 1 show lower rates of sustained virologic response than nonblacks to treatment with peginterferon plus ribavirin,1, 2 the underlying reasons for the racial differences in response rates to antiviral therapy remain obscure. I read with great interest the article by Petta et al.,3 in which the authors reported that low vitamin D serum level is related to low responsiveness to antiviral therapy in individuals chronically infected with hepatitis C genotype 1, and lower 25-hydroxy vitamin D (25(OH)D) serum level is an independent negative risk factor for sustained virologic response. I think this finding has important implications for understanding the racial differences in response rates to antiviral therapy of chronic hepatitis C.
Vitamin D levels vary in individuals of different ethnicity. Because the higher amount of pigmentation in their skin reduces vitamin D production by sunlight, blacks have been well documented to have lower vitamin D levels than that of nonblacks, and vitamin D insufficiency is more prevalent among black Americans than nonblack Americans. A cross-sectional analysis of serum 25(OH)D levels in black and white subjects enrolled in the Southern Community Cohort Study indicated that hypovitaminosis D prevalence was 45% among blacks and only 11% among whites.4 According to the finding of Petta et al. that lower 25(OH)D serum level is an independent negative risk factor for sustained virologic response for chronic hepatitis C genotype 1,3 it is reasonable to infer that the lower vitamin D levels in blacks may make them respond less well to antiviral therapy with peginterferon and ribavirin than do nonblacks.
Thus, besides the decreased prevalence among blacks of an interleukin-28B gene polymorphism associated with interferon responsiveness,5 the differences in vitamin D status among blacks and nonblacks may also contribute to the lower response rate in blacks to the antiviral treatment with peginterferon and ribavirin. Moreover, examination whether vitamin D supplementation can increase the rates of antiviral therapy response for patients, especially for blacks, infected with chronic hepatitis C virus deserves further investigation.