Ester-C? is a researched form of Vitamin C that supports immune system health. Ester-C? may lead to a more sustained retention of Vitamin C in the white blood cells than ascorbic acid in non-smokers. It is a non-acidic form of Vitamin C and may be better tolerated than standard Vitamin C in people who are sensitive to acidic foods. Nutra-Life? Ester-C? High Strength + Bioflavonoids provides 24 hour immune support and decreases the duration and severity of common cold symptoms.