Improved energy levels. B vitamins are involved in the production of energy, so taking a B-complex supplement can help to boost energy levels. Reduced fatigue. B vitamins can help to reduce fatigue by improving energy production. Improved mood. B vitamins play a role in the production of neurotransmitters, which are chemicals that send messages between brain cells. Taking a B-complex supplement can help to improve mood and reduce symptoms of depression and anxiety. Improved skin health.