The B-complex vitamins are a family of nutrients that play multifaceted and essential roles in health and preventing disease. They are needed to make and repair DNA and increase energy levels-both key steps for slowing the aging process. Some B vitamins are needed to make mood-enhancing neurotransmitters, such as serotonin, and can have powerful antidepressant benefits. The B vitamin folic acid reduces blood levels of homocysteine, a known risk factor for heart disease, stroke, cancer, and Alzheimer's disease. Vitamin B12 is needed for normal mental function, and low levels can mimic...