A recent review of the published literature on true cinnamon (Cinnamomum zeylanicum) concludes that there is evidence that the spice can lower blood pressure, cholesterol and blood glucose levels. It also has anti-microbial and anti-parasitic activity, anti-oxidant and free-radical scavenging properties, and anti inflammatory properties. There is also some evidence that it could help Alzheimer's sufferers and have a protective effect against liver disease and stomach ulcers.
Ranasinghe et al. Medicinal properties of true cinnamon (Cinnamomum zeylanicum): a systematic review. BMC Complement Altern Med Oct 2013.