Vitamin C can help fight colds. It has not yet been proven whether or not Vitamin C can prevent infections such as colds and flu (Bibliography Ref: 30, 31, 32). However, if you do catch a cold, Vitamin C can help to reduce the symptoms and speed up your recovery (Bibliography Ref: 33, 34)
Some scientific studies suggest that levels of white blood cells and Vitamin C in the body decrease when you suffer a cold (Bibliography Ref: 35, 36, 37). Therefore, taking extra Vitamin C can prevent the fall in Vitamin C levels (Bibliography Ref: 38) which suggests that the body may need a greater amount of Vitamin C during illness, especially when fighting an infection.