Cinnamon intake lowers fasting blood glucose: meta-analysis. 

This meta-analysis from 2011 assessed the effects of cinnamon extracts on blood glucose in patients with type 2 diabetes and/or prediabetes. Eight clinical studies designed as randomized, placebo-controlled trials were included. Authors concluded that results of the eight studies demonstrated statistically significant benefits for type 2 diabetics or prediabetics for lowering their blood glucose.

References:

Davis PA, Yokoyama W. Cinnamon intake lowers fasting blood glucose: meta-analysis. J Med Food. 2011 Sep;14(9):884-9. doi: 10.1089/jmf.2010.0180. Epub 2011 Apr 11. PMID: 21480806. https://pubmed.ncbi.nlm.nih.gov/21480806/