Your immune system's best friend. Vitamin C is best known for its effects on the immune system, so it is no surprise that frequent colds and infections can indicate its deficiency. This is one of the most commonly discussed vitamins, and is also known as ascorbic acid. It is water soluble and it plays a range of important roles and has a number of beneficial properties. It is a natural antioxidant and plays an important role in revitalisation, and is therefore a welcome aid in conditions of mental and physical stress. Vegetables, fruit and fruit juices are an excellent and reliable source of vitamin C.