Vitamin B-12 is well known for its energy boosting properties. It is also necessary to supplement a vegan diet with vitamin B-12. Vitamin B12 is crucial in various metabolic process in the body, and participates in red blood cell production, functioning of the nervous system, regulating sleep and mood, and even affecting levels of other compounds in the body that help in maintenance of organs such as the brain, heart and eye. Deficiency in vitamin B12 can then result in red blood cell deficiency, chronic fatigue syndrome, sleep-mood disorders or issues with peripheral nerves.