Cinnamon

There are two main types (most well known) of cinnamon, C. zeylanicum (or true cinnamon) and C. cassia (also known as C. aromatica). The type of cinnamon that you usually find in most grocery stores is C. cassia, or sometimes a mix of the two. Wherever possible in the following article references I have tried to put which species (if it was known) was used.
If you plan to use cinnamon therapeutically (consult a qualified practitioner) be aware that C. cassia contains more coumarin than does C. zeylanicum.

Diabetes

• Water soluble cinnamon extracts – reduced risk of diabetes and cardiovascular disease https://www.jacn.org/cgi/content/abstract/28/1/16
• Blood glucose– a small study showed that 6g of cinnamon reduced blood glucose and gastric emptying rate J Acad Nutr Diet. 2012 Nov;112(11):1806-9. doi: 10.1016/j.jand.2012.07.037.6/1552
• Improved insulin receptor function – activates insulin receptor PI 3-kinase and inhibits tyrosine phosphates https://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=hre50177
• Insulin resistance – study on rats fed a high fructose diet found that cinnamon improved insulin signalling Horm Metab Res 2004; 36(2): 119-125
• Protects against kidney damage – protected from nephropathy in diabetes. Planta Med 2010; 76(5): 412-417
• Cholesterol – improved serum glucose, LDL cholesterol, and total cholesterol in type 2 diabetes https://care.diabetesjournals.org/content/26/12/3215.long
  J Am Board Fam Med 2009 Sept-Oct; vol 22 no 5: 507-512.
• Regulate gene expression – water soluble cinnamon extract regulated gene expression that was involved in inflammation, insulin and lipoprotein signalling pathways Horm Metab Res. 2009 Jul;41(7):516-22.
• Reversal of effect – effects of cinnamon quickly reversed once cinnamon dosing was stopped. Eur J Appl Physiol. 2009 Apr;105(6):969-76.
• Benefit up to 12 hours after dosing – insulin and glucose modulation seem to be effective up to 12 hours after ingestion of cinnamon https://www3.interscience.wiley.com/journal/118491471/abstract

Alzheimer’s Disease

• Filament formation – in vitro study of water extract of C. zeylanicum was found to inhibit tau aggregation and filament formation (indications of Alzheimer’s disease). J Alzheimers Dis. 2009;17(3):585-97.

Anti-microbial

• Anti-fungal – activity against fluconazole-susceptible candida spp. but Fluconazole-resistant C. albicans and Candida non-albicans were less affected by cinnamon oil Can J Microbiol. 2008 Nov;54(11):950-6. doi: 10.1139/w08-097.
• E. coli and Listeria monocytogenes – C. cassia demonstrated the ability to damage the cell membranes of these infective organisms J Food Prot. 2006 May;69(5):1046-55.

Cancer

• Leukaemia – cinnamon had a dose dependant action on arresting G2/M phase of the cell cycle, caused apoptosis, and regulated progression of leukaemia cells J Nutr Biochem. 2009 Aug;20(8):614-20.

Neurological

• Neurodegenerative Disorders – through up-regulation of neurotrophic factors cinnamon may have value for treating neurodegenerative disorders. Journal of Neuroimmune Pharmacology June 2013, Volume 8, Issue 3, pp 739-755

Other

• Head lice – C. zeylanicum essential oil was tested against some of its individual constituents as well as d-phenothrin and pyrethrumto evaluate the effectiveness against head lice. the cinnamon was only slightly less effective than the d-phenothrin or pyrethru. after 24 hours of exposure no hatching was found. Int J Parasitol. 2005 Dec;35(14):1595-600.