Folic acid also known as vitamin B9 or folacin and folate in its natural form, is a part of the water-soluble B complex vitamins. Folic acid is itself not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion to dihydrofolic acid in the liver.

In the 1920s scientists believed that folate deficiency and anemia were the same condition. A key observation by researcher Lucy Wills in 1931 led to the identification of folate as the nutrient needed to prevent anemia during pregnancy. Dr. Wills demonstrated that anemia could be reversed with brewer's yeast. Folate was identified as the corrective substance in brewer's yeast in the late 1930s and was first isolated in and extracted from spinach leaves by Mitchell and others in 1941.

Bob Stokstad isolated the pure crystalline form in 1943, and was able to determine its chemical structure while working at the Lederle Laboratories of the American Cyanamid Company. This historical research project, of obtaining folic acid in a pure crystalline form in 1945, was done by the team called the "folic acid boys," under the supervision and guidance of Director of Research Dr. Yellapragada Subbarao, at the Lederley Lab, Pearl River, NY.

This research subsequently led to the synthesis of the antifolate Aminopterin, the first ever anti-cancer drug, the clinical proof of its efficacy was proven by Dr. S. Farber in 1948. In the 1950s and 1960s scientists began to discover the biochemical mechanisms of action for folate. In 1960 experts first linked folate deficiency to neural tube defects. In the late 1990s US scientists realized that despite folate being available in foods and in supplements, there was still a challenge for people to meet their daily folate requirements, and that is when the US implemented the folate fortification program.

Folate is found in small amounts in many foods. Good sources include leafy green vegetables, fruits, dried beans, peas and nuts. Enriched breads, cereals and other grain products, broccoli, Brussels sprouts, asparagus, peas, chickpeas and brown rice. Other useful sources include fortified breakfast cereals, some bread and some fruit (such as oranges and bananas).

Folic acid helps the body make healthy new cells. Everyone needs folic acid. For women who may get pregnant, it is really important. When a woman has enough folic acid in her body before and during pregnancy, it can prevent major birth defects of her baby's brain or spine. Some women have an increased risk of having a baby with a neural tube defect (NTD).

You may have a higher than average risk if:

• you have previously given birth to a baby with an NTD,
• you are taking an antiepileptic medication,
• either you, or your partner, has an NTD,
• you have a condition caused by a sensitivity to gluten (coeliac disease), or
• you have diabetes.

If any of the above applies to you, a higher dose of folic acid (5.0 mg) is recommended to reduce your chances of having a child with an NTD. This higher dose is available on prescription from your GP. Your GP or midwife may also recommend additional screening tests during your pregnancy.

Folate is a water-soluble vitamin, which means you need it in your diet every day because it can't be stored in the body. Most people should be able to get the amount they need by eating a varied and balanced diet. Adults need 0.2 mg a day. If you don't get enough folic acid from the foods you eat, you can also take it as a dietary supplement.

However, if you are pregnant or thinking of having a baby you should take a daily 0.4 mg (400 microgram) folic acid supplement from the time you stop using contraception until the 12th week of pregnancy. This is to help prevent neural tube defects such as spina bifida. If you have already had a pregnancy affected by a neural tube defect, a higher dose is recommended. Speak to your GP for more advice. See our article on the Daily Intake Rates.

Folate has a number of important functions. For example it:

• works together with vitamin B12 to form healthy red blood cells
• helps reduce the risk of neural tube defects such as spina bifida in unborn babies

Unless you are pregnant or thinking of having a baby, you should be able to get all the folate you need by eating a varied and balanced diet. If you're taking folic acid supplements, it's important not to take too much because this could be harmful. Taking 1 mg (1000 micrograms) or less of folic acid supplements a day is unlikely to cause any harm.

There are also a number of conditions that increase the risk of folic acid deficiency (not having enough in your body). Anyone taking anticonvulsant medicines, undergoing kidney dialysis, or with conditions such as liver disease, may need to supplement their diet with additional folic acid. This will also apply if you have malabsorption (difficulty absorbing vitamins and minerals) or certain types of anaemia. If you are taking medication for a medical condition, check with your GP before taking folic acid supplements.

If you're not getting enough vitamin B12 - known as vitamin B12 deficiency - taking doses of folic acid higher than 1 mg can hide this fact. An early symptom of vitamin B12 deficiency is anaemia. But taking large amounts of folic acid treats the anaemia without treating the B12 deficiency. If vitamin B12 deficiency isn't noticed, it can eventually lead to damage of the nervous system (neurological damage). This is a concern particularly for older people, because as we get older it becomes more difficult to absorb vitamin B12.