Swedish researchers published a small but interesting trial of Cinnamon (Cinnamonum verum) in the American Journal of Clinical Nutrition. Fourteen non-diabetics were in the group, and half received cinnamon powder at a dose of 6 grams in their rice pudding (clearly, not a blinded trial and much less tasty for the control group).Then, starting 15 minutes after the pudding and continuing for an hour and a half, they measured both the rate of gastric emptying and the blood sugar rise. Cinnamon slowed both down, but the effect was much greater for the blood sugar itself.
It seems to me that we are watching the synergy of crude plant preparations here: the gut is slowing down, relaxing due to the carminative volatile oils in the ground cinnamon bark. At the same time, mucilage present in the powder is binding the sugars from the meal, slowing their release into the bloodstream. Finally, there are biochemical reasons, at the level of the cell surface and the cytoplasm, why Cinnamon seems to control postprandial blood sugar very well (see additional recent studies below), but this basic idea works well for any volatile / mucilage (carminative / demulcent) combination. I hope we stay away from the idea of refining and patenting a constituent from cinnamon to treat diabetes.
The other interesting point from a clinical perspective is that this trial uses a nice (6g) dose of cinnamon for a single meal. As the studies below show, lower doses (1g to 2g per day) don't seem to do very much. This makes sense, as you need some bulk of mucilage and 1 gram of powder is a very small amount; additionally, a dose of 6g to 12g a day is much more in line with traditional usage.
Related research, via PubMed:
 Altschuler JA, Casella SJ, MacKenzie TA, Curtis KM. | | |
 | The effect of cinnamon on A1C among adolescents with type 1 diabetes. Diabetes Care. 2007 Apr;30(4):813-6. PMID: 17392542 [PubMed - indexed for MEDLINE] | |
Pham AQ, Kourlas H, Pham DQ. | | |
 | Cinnamon supplementation in patients with type 2 diabetes mellitus. Pharmacotherapy. 2007 Apr;27(4):595-9. PMID: 17381386 [PubMed - in process] | |
Cao H, Polansky MM, Anderson RA. | | |
| Cinnamon extract and polyphenols affect the expression of tristetraprolin, insulin receptor, and glucose transporter 4 in mouse 3T3-L1 adipocytes. Arch Biochem Biophys. 2007 Mar 15;459(2):214-22. Epub 2007 Jan 25. PMID: 17316549 [PubMed - indexed for MEDLINE] | |
Subash Babu P, Prabuseenivasan S, Ignacimuthu S. | | |
| Cinnamaldehyde--a potential antidiabetic agent. Phytomedicine. 2007 Jan;14(1):15-22. Epub 2006 Nov 30. PMID: 17140783 [PubMed - indexed for MEDLINE] | |
Mang B, Wolters M, Schmitt B, Kelb K, Lichtinghagen R, Stichtenoth DO, Hahn A. | | |
| Effects of a cinnamon extract on plasma glucose, HbA, and serum lipids in diabetes mellitus type 2. Eur J Clin Invest. 2006 May;36(5):340-4. PMID: 16634838 [PubMed - indexed for MEDLINE] | |
Vanschoonbeek K, Thomassen BJ, Senden JM, Wodzig WK, van Loon LJ. | | |
| Cinnamon supplementation does not improve glycemic control in postmenopausal type 2 diabetes patients. J Nutr. 2006 Apr;136(4):977-80. PMID: 16549460 [PubMed - indexed for MEDLINE] | |
Kim SH, Hyun SH, Choung SY. | | |
| Anti-diabetic effect of cinnamon extract on blood glucose in db/db mice. J Ethnopharmacol. 2006 Mar 8;104(1-2):119-23. Epub 2005 Oct 5. PMID: 16213119 [PubMed - indexed for MEDLINE] | |
Verspohl EJ, Bauer K, Neddermann E. | | |
| Antidiabetic effect of Cinnamomum cassia and Cinnamomum zeylanicum in vivo and in vitro. Phytother Res. 2005 Mar;19(3):203-6. PMID: 15934022 [PubMed - indexed for MEDLINE] | |