Here’s an excellent answer to your question:
About nine years ago (way back in 2006), I wrote about cinnamon and diabetes. To this date, people still ask questions…www.diabetesselfmanagement.com
Based on that, it seems to me that the “Yays” win, i.e. cinnamon does help reduce blood glucose in type 2 diabetes. However, what I suspect is happening that is confounding the results, is that when you believe you are taking a pill that protects you from high blood glucose, you end up cancelling out the effect by eating more sugar and carbs. So take cinnamon and reduce your carbs and sugar! Then you’ll get a doubling of the effect instead of a cancellation.