Q. I’ve heard that consuming too much cinnamon can be harmful, but what, exactly, is the acceptable limit? I eat two tablespoons on my cereal each morning just because I like the flavor and I don't need added sugar. Is that too much?
A. Some cinnamon (Chinese or cassia cinnamon) is contaminated with a natural compound called coumarin. In excess, this can harm the liver of sensitive individuals. Coumarin may also interact with blood thinners like Coumadin (warfarin) to increase the risk of bleeding.
Two tablespoons of cinnamon daily is a very big dose. You should have your liver enzymes checked when you see your doctor. People who use cinnamon to help lower blood sugar take one quarter to one half teaspoon before meals.
Unfortunately, cassia cinnamon is not labeled with the amount of coumarin it contains. This makes it hard for consumers to tell how much they are getting (Journal of Agricultural and Food Chemistry, online, Jan. 16, 2008).