Folic acid is a B vitamin (B9). Just like other B vitamins, folic acid helps your body build healthy cells and turn food into energy. Folic acid can also prevent certain birth defects (called neural tube defects) when taken before and during pregnancy.

Folic acid is sometimes called “folate,” but they’re not quite the same thing. Here’s the difference:

• Folate: Folate refers to all of the B9 forms that occur naturally in food. Foods that are high in folate include beans, leafy green vegetables, and citrus fruits. Different types of folate include dihydrofolate (DHF), tetrahydrofolate (THF), and 5-methyltetrahydrofolate (5-MTHF). 
• Folic acid: This is the synthetic (man-made) form of folate. It’s used in dietary supplements and prenatal vitamins, and added to packaged foods. It is also the only type of folate that is proven to prevent neural tube defects.

Folic acid has many different jobs in your body:

• Helps new tissues and cells grow
• Builds proteins
• Breaks food down into nutrients
• Makes red blood cells 
• Makes DNA

Folic acid is mostly used to prevent neural tube defects, and prevent or treat anemia. 

Folic acid: Sources and supplements

Folic acid does not occur naturally in foods. You can get folic acid by:

• Taking a folic acid supplement
• Eating packaged foods with folic acid added (like enriched cereals, breads, and rice)

Keep in mind: There are other types of folate (like 5-MTHF) found in foods, and available as supplements. But these are not the same thing as folic acid.

Folic acid is the only type of folate proven to prevent neural tube defects. Though folate-rich foods are generally nutritious and good for your health, women should also take a supplement and/or eat folic acid-fortified foods.

Folic acid dosing

The recommended daily doses of folic acid for women are:

• All women age 14 and older: 400 mcg 
• Pregnant women: 600 mcg 
• Pregnant women expecting twins: 1,000 mcg 
• Nursing women: 500 mcg

If you’ve had a previous pregnancy with a neural tube defect, the recommendations are different:

• If you’re currently trying to get pregnant again, the CDC recommends consuming 4,000 mcg each day. You should start this dose 1 month before getting pregnant and continue it through the first trimester (3 months) of your pregnancy. 
• If you’re not planning to get pregnant, you should get 400 mcg of folic acid per day  — either from a supplement and/or by eating fortified foods. You should do this even if you’re not currently planning to get pregnant.

If you’re taking a medication called methotrexate (Trexall), you may be instructed to take a folic acid supplement during treatment. These doses tend to be higher — either 1,000 mcg once daily or 5,000 mcg once weekly.

You should not take more than 1,000 mcg of folic acid per day. Taking too much folic acid can cause side effects. It can also potentially make it harder to tell if you have a B12 deficiency.

You need to take folic acid every day for it to be effective. Unlike other vitamins and hormones, your body doesn’t store folic acid. Any leftover folic acid will pass out of your body in your urine. If you stop consuming folic acid, the levels in your body will slowly go down. 

Common uses for folic acid supplements

Folic acid supplements are used for:

• Preventing neural tube defects in babies
• Preventing and treating anemia
• Preventing side effects from taking methotrexate
• Treating a folate deficiency

There’s also evidence that consuming folic acid can help:

• Prevent stroke
• Prevent heart disease
• Lower the risk of arsenic poisoning

The science behind folic acid

Most vitamin supplements don’t have a proven benefit. But that’s not the case with folic acid.

The evidence is clear: Folic acid prevents birth defects. This includes neural tube defects, like spina bifida and anencephaly. In fact, folic acid is so important that the FDA requires it to be added to all fortified grains, pasta, bread, and cereals — to help U.S. women get enough folic acid in their diet.

There’s also evidence that folic acid may help lower your risk of stroke and heart disease. In a large 2018 research study, taking a daily dose of 800 mcg of folic acid reduced the risk of stroke by 21% in adults with hypertension. And a 2016 meta-analysis suggested that people who take a folic acid supplement may have a 10% lower risk of stroke and a 4% lower risk of heart disease. 

Folic acid supplement interactions

Certain medications can interfere with how folic acid is absorbed or broken down by your body.

Examples of these medications include:

• Anti-seizure medications like phenytoin (Dilantin), carbamazepine (Tegretol), and gabapentin (Neurontin)
• Sulfasalazine (Azulfidine)
• Sulfamethoxazole/trimethoprim (Bactrim)

Phenytoin can lower folic acid levels. But it’s also thought that folic acid supplementation can make phenytoin less effective. Your healthcare provider may need to adjust your phenytoin dose if you’re taking both.

Methotrexate is a medication that prevents your body from using folic acid. If you’re taking it for an autoimmune condition, you may be instructed to take a folic acid supplement during treatment. But if you’re taking methotrexate for cancer, you may be advised not to take folic acid. It’s thought that folic acid can potentially affect how well methotrexate works for cancer.

Folic acid supplement side effects

Folic acid doses up to 400 mcg per day are generally considered safe. This dosing range also tends to be well tolerated. Most of the side effects of folic acid are linked to high doses (e.g., 15 mg daily).

Examples of these side effects include:

• Loss of appetite
• Nausea
• Bloating
• Passing gas
• Bad taste in your mouth
• Sleeping problems
• Concentration problems
• Feeling irritable

Safety of folic acid supplements

Your liver only processes a certain amount of folic acid at a time, and your body gets rid of any extra folic acid it doesn’t use through your kidneys. There isn’t enough evidence to say that having extra folic acid in the blood is harmful. But this doesn’t mean you should take more than the recommended amount. As mentioned above, higher doses can cause side effects.

Folic acid supplements are available in oral and injectable forms. Although rare, serious allergic reactions have been reported with both types. Get medical attention right away if you develop symptoms like skin rash, itching, or trouble breathing.

Folic acid injections contain small amounts of aluminum. People with kidney problems may not be able to clear it from their bodies as well. This can cause aluminum to build up and become toxic.

As mentioned above, high doses of folic acid can potentially cover up symptoms of a B12 deficiency. When left untreated, B12 deficiency can cause nerve damage.

FAQs

Will taking folic acid help me get pregnant?

No. Folic acid will not help you conceive — but it will protect your baby from neural tube defects if you do get pregnant.

Since many pregnancies are unplanned, and neural tube defects happen during the first few weeks of pregnancy, all women of childbearing age should get 400 mcg of folic acid every day.