Folic acid or folate is a B vitamin. It is also referred to as vitamin M, vitamin B9, vitamin Bc (or folacin), pteroyl-L-glutamic acid, and pteroyl-L-glutamate. The term folate is often used in the food supplement industry to denote something different than “pure” folic acid: in chemistry, the term folate refers to the deprotonated ion and folic acid to the neutral molecule, which both co-exist in water. (The International Union of Pure and Applied Chemistry and the International Union of Biochemistry and Molecular Biology clearly state that “folate and folic acid are the preferred synonyms for pteroylglutamate and pteroylglutamic acid, respectively.) The term folate in the food industry often refers to “the natural occurring form of folic acid”. There is no “natural” and chemical form of folate and folic acid, and the two terms can be used interchangeably. It is likely that in the food industry, the term “folate” is used to indicate a collection of “folates” which is not chemically well-characterized, including other members of the family of pteroylglutamates, or mixtures of them, having various levels of reduction of the pteridine ring, one-carbon substitutions and different numbers of glutamate residues, all of which can be found in nature. Folic acid is synthetically produced, and used in fortified foods and supplements. Folate is converted by humans to dihydrofolate (dihydrofolic acid), tetrahydrofolate (tetrahydrofolic acid), and other derivatives, which have various biological activities. Vitamin B9 is essential for numerous bodily functions. Humans cannot synthesize folates de novo; therefore, folic acid has to be supplied through the diet to meet their daily requirements. The human body needs folate to synthesize DNA, repair DNA, and methylate DNA as well as to act as a cofactor in certain biological reactions. It is especially important in aiding rapid cell division and growth, such as in infancy and pregnancy. Children and adults both require folate to produce healthy red blood cells and prevent anemia. Folate and folic acid derive their names from the Latin word folium, which means “leaf”. Folates occur naturally in many foods and, among plants, are especially plentiful in dark green leafy vegetables. A lack of dietary folates can lead to folate deficiency. A complete lack of dietary folate takes months before deficiency develops as normal individuals have about 500–20,000 µg of folate in body stores. This deficiency can result in many health problems, the most notable one being neural tube defects in developing embryos—a relatively rare birth defect affecting only 300,000 (0.002%) of births globally each year. Common symptoms of folate deficiency include diarrhea, macrocytic anemia with weakness or shortness of breath, nerve damage with weakness and limb numbness (peripheral neuropathy), pregnancy complications, mental confusion, forgetfulness or other cognitive deficits, mental depression, sore or swollen tongue, peptic or mouth ulcers, headaches, heart palpitations, irritability, and behavioral disorders. Low levels of folate can also lead to homocysteine accumulation. Low levels of folate have been associated with specific cancers. However, it is not clear whether consuming recommended (or higher) amounts of folic acid—from foods or in supplements—can lower cancer risk in some people.