Folate (vitamin B-9) is important in red blood cell formation and for healthy cell growth and function. The nutrient is crucial during early pregnancy to reduce the risk of birth defects of the brain and spine.

Folate is found mainly in dark green leafy vegetables, beans, peas and nuts. Fruits rich in folate include oranges, lemons, bananas, melons and strawberries. The synthetic form of folate is folic acid. It's in an essential component of prenatal vitamins and is in many fortified foods such as cereals and pastas.

A diet lacking foods rich in folate or folic acid can lead to a folate deficiency. Folate deficiency can also occur in people who have conditions, such as celiac disease, that prevent the small intestine from absorbing nutrients from foods (malabsorption syndromes).

The recommended daily amount of folate for adults is 400 micrograms (mcg). Adult women who are planning pregnancy or could become pregnant should be advised to get 400 to 1,000 mcg of folic acid a day.

Research on use of folate and oral folic acid supplements for specific conditions shows:

• Birth defects. Research has shown that folic acid supplements can prevent birth defects of the neural tube. Taking a daily prenatal vitamin — ideally starting three months before conception — can help ensure women get enough of this essential nutrient.
• Folic acid deficiency. Nutritional folate deficiency is treated with oral folic acid supplements. This type of deficiency is no longer a problem in many countries that fortify foods such as cereal and pasta with folic acid.
• Heart and blood vessel disease and stroke. Folic acid works with vitamins B-6 and B-12 to control high levels of homocysteine in the blood. Elevated homocysteine levels might increase your risk of diseases of the heart and blood vessels (cardiovascular disease).
• Cancer. Some research suggests that folate might reduce the risk of various cancers.
• Depression. Some evidence suggests that folic acid might be helpful in treating depression.
• Dementia. There isn't enough evidence to support folic acid supplementation for the prevention of dementia.

When used orally at appropriate doses, folic acid is likely safe.

Oral use of folic acid can cause:

• Bad taste in your mouth
• Nausea
• Loss of appetite
• Confusion
• Irritability
• Sleep pattern disturbance

People with allergies might have a reaction to folic acid supplements. Warning signs of an allergic reaction include:

• Skin rash
• Itching
• Redness
• Difficulty breathing

Excess folic acid is excreted in urine.

A high folate intake can mask vitamin B-12 deficiency until its neurological effects become irreversible. This can typically be remedied by taking a supplement containing 100 percent of the daily value of both folic acid and vitamin B-12.

Possible interactions include:

• Anticonvulsants. Taking folic acid with fosphenytoin (Cerebyx), phenytoin (Dilantin, Phenytek) or primidone (Mysoline) might decrease the drug's concentration in your blood.
• Barbiturates. Taking folic acid with a drug that acts as a central nervous system depressant (barbiturate) might decrease the drug's effectiveness.
• Methotrexate (Trexall). Taking folic acid with this medication used to treat cancer could interfere with its effectiveness.
• Pyrimethamine (Daraprim). Taking folic acid with this antimalarial drug might reduce the effectiveness of the drug.