Clinical Research on Cinnamomi Cortex: A Scoping Review

Abstract

There are over 250 species of cinnamon. Each has its distinct morphology and phytochemical composition, which may result in varied therapeutic effects. However, clinical studies have rarely put emphasis on the species of cinnamon being investigated. This scoping review summarized the clinical evidence of Cinnamomum cassia (also known as Cinnamomum aromaticum), which is the species of cinnamon used in traditional Chinese medicine. Electronic searches were conducted on PubMed from its inception till August 2021. Clinical studies that were published in English, stating monotherapy with Cinnamomum cassia, Cinnamomum aromaticum, or "Rou Gui" were included. The 15 included clinical studies investigated the effects of Cinnamomum cassia on type-2 diabetes patients (n=7), and healthy adults (n=8). In the type 2 diabetes population, Cinnamomum cassia supplementation of as low as 1 g/d seemed to improve HbA1c in only poorly controlled diabetes. In the healthy population, Cinnamomum cassia supplementation appeared to influence blood glucose response in a dose-dependent manner, with current studies indicating a minimum of 5 g/dto achieve significant improvement. Studies also showed potential improvement in insulin sensitivity with prolonged Cinnamomum cassia supplementation. However, there were apparent heterogeneity among studies and uncertainties regarding the accuracy of reported cinnamon species. Therefore, the therapeutic effects of Cinnamomum cassia remain inconclusive. Future larger scale and more rigorous clinical studies, with clear identification of Cinnamomum species used, are needed for more conclusive evidence of the clinical effects of Cinnamomum cassia.