Vitamin B' refers to eight different B vitamins in total. If you take a supplement that contains all eight of the B vitamins, this is referred to as a 'vitamin B complex' or 'B complex' formula which will include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate or 'folic acid' when included in supplements (B9), cyanocobalamin (B12). Vitamins B1, B2, B3, B5 and B6 contribute to normal energy-yielding metabolism. Vitamins B1, B3, and B6 contribute to normal functioning of the nervous system. Folate, vitamin B5 and B12 contribute to the reduction of tiredness and fatigue.