Vitamin B3 is needed for proper circulation and healthy skin. It aids in the functioning of the nervous system and plays a key role in the production of the sex hormones. It promotes healthy digestion and can help relieve gastric disturbances. It is helpful for schizophrenia and other mental illnesses and is also a memory-enhancer. Signs of vitamin B3 deficiency: Tiredness, irritability, food rages due to blood sugar fluctuations and canker sores.