How many B vitamins is folic acid? Folic acid is a water-soluble vitamin also known as vitamin B9, vitamin M or oxalate methyltetrahydrofolate. Since the body cannot synthesize folic acid on its own, it must be obtained from food or through supplements. Folic acid plays a very important role in the human body. It is involved in the synthesis of functionally important substances such as DNA, RNA, and nuclear proteins. It can also regulate the immune system, promote cell division and development, and protect the health of the cardiovascular system. leaf