As well as supporting immunity, Vitamin C is needed for many important functions in the body including energy production and combatting tiredness and fatigue. What is Vitamin C Effervescent?. One tablet typically provides 500mg Vitamin C, citric acid, sodium bicarbonate, fruit sugar, Ascorbic acid (Vitamin C), natural lemon, (with 20mg (0.08 kcal) sugar), natural colours: red beet, vitamin B2.