 Second in spice popularity, only to black pepper, cinnamon is the powdered inner bark of four different species of cinnamonum trees. There's Vietnamese cinnamon, Chinese cinnamon, Indonesian and Ceylon. A recent review raised concerns about one of them because of a compound called cumarin, which new human data suggests may be toxic to the liver. It's been banned as a food additive, but still can be found naturally in Chinese cinnamon, also known as cassia cinnamon. It is not found in significant amounts in so-called true cinnamon, Ceylon cinnamon, and we don't have enough data on the other two. Now these traffic lights are not for recreational users. These are only for people going out of their way to add like a teaspoon or more to their daily diet, which ideally should be everyone, since it appears so health-promoting. Anti-inflammatory, anti-microbial, anti-oxidant, anti-tumor, cardiovascular, cholesterol-lowering, and immunomodulatory effects, especially useful for those with diabetes or pre-diabetes. So if you're eating cinnamon every day, great. Just make sure it's the right kind. In the UK, if it's a cinnamon, then it's Ceylon cinnamon. Chinese cinnamon is labeled cassia. In the US, though, they can both just be labeled cinnamon, and since Chinese is cheaper, that's what most cinnamon is on our shelf. So make sure it specifies Ceylon.