Vitamins B1, B2, niacin (B3), B6, pantothenic acid, and vitamin C contribute to the reduction of tiredness and fatigue. Vitamins B1, niacin (B3), B6, B12, biotin, and vitamin C contribute to the normal functioning of the nervous system and normal psychological function. Vitamin C is an antioxidant nutrient that contributes to the protection of cells from oxidative stress and to the normal functioning of the immune system. As a water-soluble nutrient vitamin C supplies in the body are used up quicker under stress leading to a lowering of immune function and increased incidence of infections.