One of the oldest spices in the world, when brewed cinnamon releases its essential oil, cinnamonaldehyde, which acts in the body to encourage circulation, relieve nausea and improve digestion. Studies have shown that cinnamon regulates blood sugar, is effective against some bacteria, reduces pain linked to arthritis and calms menstrual pain. As a nutritional plant, cinnamon contains fibre, calcium, iron and manganese.