Review question

Is vitamin D supplementation beneficial or harmful for people with chronic liver diseases?

Background

The available evidence on vitamin D and chronic liver diseases is inconclusive. Many observational studies (a study of a group of people where the researcher has no control of treatments and conditions because of ethical concerns or logistical constraints) suggest that chronic liver diseases are associated with low vitamin D levels in the blood. Therefore, improving vitamin D levels could have beneficial effects on chronic liver diseases. Results of randomised clinical trials (trials where people are randomly assigned into one of two or more treatment groups) testing the effect of vitamin D supplementation for chronic liver diseases are contradictory. The aim of this systematic review (a summary of results of available healthcare trials) was to analyse the benefits and harms of the different forms of vitamin D in people with chronic liver diseases.

Study characteristics

Fifteen trials provided data for this review; 1034 adult participants were randomly assigned to vitamin D compared with placebo or no treatment. Nine trials were conducted in high-income countries, and six trials in middle-income countries. All trials were at high risk of bias (that is overestimation of benefits and underestimation of harms). The age range of the participants was 18 years to 84 years and on average 42% were women. Six trials included participants with chronic hepatitis C, four trials included participants with liver cirrhosis, four trials included participants with non-alcoholic fatty liver disease, and one trial included liver transplant recipients. Most of included trials reported the baseline vitamin D status of participants. Vitamin D administration lasted on average six months and most trials used the cholecalciferol (vitamin D₃) form.

Funding

Six trials appeared to be free of industry sponsorship or other type of for-profit support that may bias the results of the trials. Eight trials may not have been free of for-profit bias as they did not provide any information on clinical trial support or sponsorship. One trial was funded by industry.

Key results

This review suggests that vitamin D has no beneficial or harmful effects on chronic liver diseases. However, there were too few trials on the individual diagnosis of chronic liver diseases and there were too few participants in the individual trials as well as in our meta-analysis. Therefore, neither benefits nor harms can be excluded.

Quality of the evidence

All trials were judged to be at high risk of bias (that is, possibly an overestimation of benefits and underestimation of harms).

Currentness of evidence

This evidence is up to date as of January 2017.