Be careful with Cinnamon, especially the variety commonly sold in supermarkets because it is Cassia Cinnamon and it contains Coumarin which is a liver toxin and antocoagulant.
A teaspoon of cassia cinnamon a day is above the level thought to be safe for the amount of coumarin it contains. Anyone who is already on any anticoagulant should not take cinnamon as a supplement because it can increase the risk of internal bleeding. Coumarin is also a known carcinogen and has been banned from use in tobacco products and perfumes. In the small amounts normally used in cooking and baking, cassia cinnamon is thought to be relatively safe.
Of the four varieties of bark sold under the name of cinnamon, the safest is cinnamomum verum (Sri Lanka cinnamon) which contains a very negligible amount of coumarin. Unfortunately, if you can find it, it is very expensive. I've tried it as a supplement and found it didn't produce the reduction in blood glucose claimed by the quackery of Dr. Mercola, and Dr. Oz and all the others. It was certainly not worth the £14 for a bottle of 60 capsules.
Having said all that, I still like cinnamon in my oatbran porridge and on my yoghurt, I just don't use more than needed to flavour my food.