Curcumin as a potential therapeutic option for NAFLD and other metabolic diseases: need for establishing the underlying mechanism(s) of action
The natural polyphenol, curcumin, the most widely studied component of the Asian spice Turmeric, is shown to have potent anti oxidant, anti inflammatory, anti bacterial and anti neoplastic activities [1 4] These varied beneficial effects have been largely examined using cell culturebased assays in vitro where curcumin is in direct contact with the target cells. However, limited oral bioavailability of curcumin and levels of curcumin or its metabolites in systemic circulation below the detection limits of most analytical methods hinder the establishment of a cause effect relationship between orally administered curcumin and the observed beneficial effects in vivo [5] Furthermore, results from several small scale clinical studies/trials have not been entirely consistent complicating an already difficult problem. Nonetheless, ever increasing published data and widespread recognition of curcumin as a dietary supplement warrant a systematic review of existing literature, preferably in the context of a specific disease process. In this issue of the Journal, Wei et al. [6] report a metaanalysis of randomized controlled trials (RCTs) examining the effects of curcumin on the metabolic parameters of nonalcoholic fatty liver disease (NAFLD) Out of 99 studies identified by literature searches, only four studies met the stringent inclusion criteria namely, RCT or parallel trial, included subjects 18 years of age, assessment of NAFLD (grades 1 3) by liver ultrasound and the fact that the intervention group received curcumin and control group received a placebo. Curcumin supplementation significantly lowered plasma LDL C, triglycerides, fasting blood sugar, HOMAIR, body weight and AST levels. However, the observed lowering of total plasma cholesterol, HDL C, HbA1c, ALT or insulin levels by curcumin did not reach statistical significance. Detailed analyses on the effects of curcumin on the severity of hepatic steatosis, an important parameter for NAFLD, could not be performed due to the limited number of available studies. Despite another limitation noted by the authors, namely small number of patients included in most studies, these are promising/encouraging data especially considering the poor bioavailability of orally administered curcumin and raise two intriguing possibilities:
Hepatology International