Vitamin B6 is a B vitamin that is needed for more than 100 different reactions in the body. It is critical for proper brain function, to manufacture neurotransmitters, and it helps regulate mood. The vitamin may protect against colorectal cancer, memory loss, and premenstrual syndrome (PMS). Good sources of this vitamin include beef liver, lean meat, legumes, fish, leafy greens, starchy vegetables like potatoes, and fruits (excluding citrus fruit). Fortified cereals have the vitamin, too. Vitamin B6 deficiency may result in muscle weakness, irritability, depression, nervousness, trouble concentrating, and short-term memoryloss.