Ester-C Supreme is a citrus-free vitamin C formula with antioxidant bioflavonoids & immune-boosting arabinogalactan. This antioxidant-rich Ester-C formula supports immune health, as well as skin, joints, and vision. Clinical studies show that Ester-C increases vitamin C levels in the body for up to 24 hours. Regular vitamin C is first buffered with calcium, then a special process transforms it into trademarked Ester-C. This vegan, non-GMO formula contains no dairy, gluten, or soy. Gentle On The Stomach; Sisu Ester-C Supreme is a less-acidic vitamin C that is gentle on the digestive system.