Yokoyama 2014.

Methods	Randomised clinical trial with parallel group design (2 groups).
Participants	84 participants (49% women), aged 30 to 78 years, mean age 59 years, with HCV genotype 1b. Inclusion criteria: aged ≥ 20 years, chronically infected with HCV genotype 1 and plasma HCV RNA concentrations ≥ 100 log IU/mL. Exclusion criteria: decompensated cirrhosis, liver cancer, HBV or HIV infection, renal insufficiency, history of heart disease or cerebral infarction, pregnancy or breastfeeding.
Interventions	Intervention: subcutaneous injections of PEG‐IFN‐α‐2b (1.5 μg/kg body weight) once weekly, along with weight‐based oral ribavirin (600 mg/day to 1200 mg/day) + vitamin D3 1000 IU (n = 42). Control: subcutaneous injections of PEG‐IFN‐α‐2b (1.5 μg/kg body weight) once weekly, along with weight‐based oral ribavirin (600 mg/day to 1200 mg/day) (n = 42). For 16 weeks.
Outcomes	Primary outcome: undetectable HCV RNA at week 24. Secondary outcomes: none stated.
Stated aim of study	To rigorously evaluate the antiviral effects of vitamin D supplementation in people with HCV genotype‐1 infection being treated with PEG‐IFN + ribavirin.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of sequence generation not specified.
Allocation concealment (selection bias)	Unclear risk	Method used to conceal the allocation not described so intervention allocations may have been foreseen before, or during, enrolment.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding, and outcome was likely to be influenced by lack of blinding.
Blinding of outcome assessment (detection bias) All outcomes	High risk	No blinding of outcome assessment, and outcome measurement was likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Missing data were unlikely to make treatment effects depart from plausible values.
Selective reporting (reporting bias)	Unclear risk	Unclear whether all predefined and clinically relevant and reasonably expected outcomes were reported.
For‐profit bias	Unclear risk	Trial may or may not have been free of for‐profit bias as trial did not provide any information on clinical trial support or sponsorship.
Other bias	Low risk	Trial appeared to be free of other factors that could put it at risk of bias.

ALT: alanine aminotransferase; AST: aspartate aminotransferase; BMI: body mass index; EVR: early viral response; HBV: hepatitis B virus; HCV: hepatitis C virus; HDV: hepatitis D virus; IFN: interferon; IU: international unit; MRI: magnetic resonance imaging; n: number of participants; NAFLD: non‐alcoholic fatty liver disease; PCR: polymerase chain reaction; PEG: pegylated; RNA: ribonucleic acid; RVR: rapid viral response; SVR: sustained virological response; US: ultrasound; WBC: white blood cell count.