Folate, also called folic acid, folacin, or vitamin B9, is a water-soluble B-complex vitamin that is essential for human growth and development. It is made up of three components: para-aminobenzoic acid (PABA), glutamic acid, and pteridine. The latter two components explain the technical chemical name for folate: pteroylmonoglutamate. Because folate is one of the most chemically complex vitamins, it is also complicated in its interaction with your body. Most foods do not contain folate in the exact form described above, so enzymes inside your intestines must chemically alter food forms of folate in order for you to absorb it. Even when your body is operating at full efficiency, you can absorb only about 50% of the folate from your food.

It is important in cell division and DNA synthesis, and is required to properly transcribe DNA, transform norepinephrine into adrenalin, as well as transform serotonin into melatonin. Folate also works with vitamins B6 and B12 to suppress the toxic amino acid homocysteine, an amino-acid byproduct that damages artery walls, promotes inflammatory conditions and platelet clotting as well as atherosclerotic plaque formation, which contributes to the hardening of blood vessels and can result in the development of cardiovascular disease and many other health problems. Decreasing homocysteine levels protects your heart and blood vessels. Folate, along with vitamins B6 and B12, convert homocysteine into cysteine or methionine, both of which are harmless. Folate might also help protect against cancers of the lung and cervix, and may help slow memory decline associated with aging. Folate works with vitamin B12 to help prevent cognitive impairment.

Folate can:

• Prevent birth defects: Folate supports the growth of the placenta and fetus, and it helps to prevent several types of birth defects, especially those of the brain and spine, such as malformation of the neural tube. As a fetus develops, the top part of this tube helps form the baby’s brain, and the bottom part becomes the baby’s spinal column. If the neural tube fails to close properly, the baby can be born with serious brain and spinal problems. Mothers with inadequate supplies of folate give birth to a greater number of infants with neural tube defects. Beginning in the early 1980’s, researchers began to successfully use folate supplementation to reduce the risk of nervous system problems in newborn infants. In addition, adequate folate intake prevents cleft lip and palate. Because defects can occur in an embryo before a woman realizes that she’s pregnant, it’s important for all women ages 15 to 45 to include folate in their diets.
• Support red blood cell production and help prevent anemia: Folate allows for the complete development of red blood cells, which help carry oxygen around your body. When folate is deficient, your red bloods cannot form properly, and continue to grow without dividing in a condition called macrocytic anemia.
• Help prevent cardiovascular disease and cancer: Folate helps maintain healthy circulation of your blood throughout your body by preventing build-up of a substance called homocysteine. A high serum homocysteine level (called hyperhomocysteinemia) is associated with increased risk of cardiovascular disease and cancer, and low intake of folate is a key risk factor for hyperhomocysteinemia. Increased intake of folate can lower your risk of cardiovascular disease and cancer by preventing build-up of homocysteine in your blood.
• Support healthy skin, mouth, gums, lungs, intestines, and other tissues: Cells with very short life spans (like skin cells, intestinal cells, and most cells that line your body’s exposed surfaces or cavities) are highly dependent on folate for their creation. For this reason, folate deficiency has repeatedly been linked to problems in these types of tissue. In your mouth, these problems include gingivitis and periodontal disease. In your skin, the problems include seborrheic dermatitis and vitiligo (loss of skin pigment). Cancers of the esophagus and lung, uterus and cervix, and intestine (especially the colon) have been repeatedly linked to folate deficiency.
• Allow nerves to function properly: Deficiency of folate has been linked to a wide variety of nervous system problems, including general mental fatigue, dementia, depression, restless leg syndrome, nervous system problems in the hands and feet, irritability, forgetfulness, confusion, and insomnia. Folate helps synthesize your nervous system’s message-carrying molecules, called neurotransmitters, and helps keep them in balance and keep you happy. High homocysteine levels caused by deficiency of folate can also lead to the deterioration of dopamine-producing brain cells and may therefore contribute to the development of Parkinson’s disease.
• Promote a good mood: Folate is responsible for mood, the healthy functioning of your nerves, memory retrieval, processing speed, and protecting you from depression. When a deficiency is present, you may suffer from feelings of depression, irritability and mental fatigue.  Studies show that up to 50 percent of those suffering depression have low folate levels. Although researchers don’t yet fully understand the connection, folate deficiency appears to impair the metabolism of serotonin, dopamine, and noradrenaline, neurotransmitters important for mood. Higher concentrations of folate in the blood are linked to a decrease in negative moods and clinical depression.
• Help prevent osteoporosis-related bone fractures: Low levels of folate significantly increases your risk of osteporosis-related bone fractures due to the resulting increase in homocysteine levels. People with the highest levels of homocysteine also have a much higher risk of osteoporotic fracture. Conversely, folate reduces the risk of osteoporotic fractures by reducing high levels of homocysteine.
• Help prevent dementias, including Alzheimer’s disease: Low blood levels of folate are also linked to dementias, including Alzheimer’s disease. People whose blood levels of folate were lowest had more than triple the risk for mild cognitive impairment, and risk of dementia increased almost four fold. Homocysteine, a potentially harmful product of cellular metabolism that is converted into other useful compounds by folate, along with vitamin B6 and B12, was also linked to dementia and Alzheimer’s disease. People whose homocysteine levels were elevated had a more than four-fold increased risk of dementia and an almost four-fold increased risk of Alzheimer’s disease.

Because of its link with the nervous system, folate deficiency can be associated with irritability, mental fatigue, forgetfulness, confusion, depression, and insomnia. The connections between folate, circulation, and red blood cell status make folate deficiency a possible cause of general or muscular fatigue. The role of folate in protecting the lining of body cavities means that folate deficiency can also result in intestinal tract symptoms (like diarrhea) or mouth-related symptoms like gingivitis or periodontal disease.