The results of this study suggest that the addition of a vitamin D supplement to current standard therapy can significantly improve the rate of SVR in treatment-naïve patients with HCV genotype 2-3, compared to the rates with standard therapy alone. The observed SVR rate in the control group (77%) is consistent with previous reports[2,3
]. The overall responses reflect a marked increase in the rate of virological response at week 24 after cessation of therapy (95% vs
77%) and a low rate of non-response (5% vs
23%) with vitamin-D-based treatment, as compared to the control group[19
There are only two reports dealing with the association between vitamin D status and outcome of antiviral therapy for chronic HCV viral infection. Petta et al[13
] have retrospectively analyzed a cohort of 167 patients treated with peg-interferon and ribavirin for hepatitis C, and detected an association between lower vitamin D serum levels and failure to achieve SVR. Our results provide further support to these data. The second study by Bitetto et al[20
] has shown that vitamin D supplementation improves response to antiviral treatment for recurrent hepatitis C in liver transplant recipients. Several differences between those two studies should be noted. Their HCV patients were immunocompromised and they were supplemented by low-dose vitamin D (800 IU/d) after liver transplantation. In addition, most of their HCV patients (75%) had low vitamin D levels despite treatment. Finally, that study was retrospective and focused on the prevention of osteoporosis and not on the treatment of hepatitis C. Very recently, Southern et al[15
] have shown the beneficial effect of vitamin D supplementation on the outcome in patients with chronic HCV genotype 2-3 infection. However, this study was retrospective and the authors used Calcichew D3 Forte during the course of treatment without indicating the dose or serum levels of vitamin D.
The exact mechanism of action leading to improved response to antiviral treatment is unknown in patients receiving vitamin D. Vitamin D is metabolized by the liver and is converted to 1,25 dihydroxyvitamin D3, which is the active form of the vitamin[6,7
]. Those with chronic liver disease may have poor conversion from vitamin D3 or any of its other biologically active metabolites[11
]. 1,25 vitamin D3 appears to modulate immunity principally via regulating T-cell function[21
]. The vitamin D receptor (VDR) is expressed on virtually every type of cell involved in immunity[22
]. The immunomodulatory actions of vitamin D are elicited through its direct action on T-cell antigen-presenting cell function[23
]. T helper cell type 1 (Th1) cell actions are intensified when vitamin D is insufficient, as in the majority of our patient population, or when signals through VDR are weak. Regulatory T cells and Th2 cells are diminished, thus favoring an autoimmune Th1 response[24
]. This is a proinflammatory response that may impair interferon and insulin signaling, thus decreasing viral response[25,26
]. A recent study, comprised of 120 patients with chronic infection with HCV genotype 1 reported a Th1 to Th2 ratio < 15.5 (OR, 9.6) was significantly associated with SVR[27
]. The overall effect is a switch from the Th1/Th17 response to the Th2/Treg profile[28
]. However, Th1 and Th2 measurement was not performed in the present study. Persistent HCV infection modulates the balance between immunostimulatory and inhibitory cytokines that can prolong inflammation and lead to fibrosis and chronic liver diseases[29
]. More recently, Gutierrez et al[30
] have shown that vitamin D3 increases VDR protein expression and inhibits viral replication in cell culture.
It is well known that people of African and Hispanic descent are less likely to respond to standard therapy[31
]. This may be due to a polymorphism of the IL28B
gene and to vitamin D deficiency[13,32
]. The vast majority of subjects in the present study had vitamin D insufficiency that was possibly related to low exposure to the sun and/or to a low supply of vitamin D from the diet. Recently, an important study by Lange et al[33
] has confirmed the association of response to therapy with vitamin D levels and, even more significantly, by describing novel associations between genetic polymorphisms within VDR; especially in the α-hydroxylase promoter region (CYP27B1-1260), and vitamin D levels in HCV patients. The authors showed also that fibrosis alone is not the key to understanding the impact of chronic hepatitis C on vitamin D metabolism.
The role of insulin resistance and supplementation of vitamin D with regards to chronic HCV infection has been investigated previously by our group[14
]. Insulin resistance has emerged as one of the most important host factors in the prediction of response in non-diabetic HCV-infected patients treated with Peg/RBV, and is a common denominator to the majority of features associated with difficult-to-treat patients[34
]. Vitamin D is also known to help prevent type 2 diabetes and it is possible that low levels of vitamin D lead to insulin resistance[9
]. The direct effect of vitamin D may be mediated by binding of its circulating active form to the pancreatic B cell VDR[35,36
]. Moreover, oxidative stress leaches calcium, and vitamin D helps absorb calcium[37
]. In the current study, increasing levels of vitamin D to > 32 ng/mL increased the response to antiviral therapy. The calcium levels were normal in our patient population.
Multivariate analysis revealed that vitamin D supplementation, baseline vitamin D levels, viral load, and hepatitis C genotype remained as independent predictors. Thus, it can be concluded that vitamin D supplementation is responsible for a higher SVR, rather than the baseline vitamin D level. Limitations of the present study include the small number of patients, and the lack of Th1 and Th2 immune response. The identification of determinants of response such as polymorphisms of the IL28B
gene and within the VDR may explain the difference in response rates between patients with different ethnic backgrounds. This was not done in our study because data on IL-28B
and VDR polymorphism were not available. Because of the small number of patients in the present study, a multicenter study with a larger number of patients is warranted. Another limitation was the lack of results that documented the viral response at weeks 4 and 12 in the control group. This test was not included in the health package at the time of study recruitment. Finally, we did not have a dose-response relationship for vitamin D supplementation. The dose of 2000 IU/d was based on previous investigations[38
In conclusion, the addition of vitamin D to pegylated interferon α2b and ribavirin in naïve patients infected with HCV genotype 2-3 significantly increased the rate of viral response. We suggest routine testing of vitamin D levels prior to combination therapy and replacement during treatment for chronic hepatitis C.