According to reports from Germany, spices often sold as cinnamon contain cumarin, which can damage the liver and kidneys. It’s been banned as a food additive in many countries since the middle of the last century.
True cinnamon does not contain the toxic substance, but the related species cassia is often sold under the same name. The Swedish National Food Administration has issued a warning against nutritional supplements containing large amounts of cinnamon.
But, the agency says, there’s no danger in sprinkling some cinnamon on to a traditional Swedish Christmas porridge.