Folic acid is a synthetic form of vitamin B9 that’s often added to fortified foods and used in supplements. It has numerous benefits, and some risks.
Folic acid is a water-soluble vitamin. It’s a synthetic version of folate, one of the B vitamins (1).
Because your body can’t make folate, you need to get it from your diet.
Some foods naturally contain folate. Folic acid is added to other foods. You can also get folic acid from dietary supplements (2).
Although the terms “folate” and “folic acid” are often used interchangeably, they are actually different forms of the same vitamin: vitamin B9.
Folic acid has a different structure than folate and has slightly different effects in your body. “Folate” is the generic name that encompasses all forms of vitamin B9, including folic acid and 5-MTHF. Folic acid is a specific synthetic form of this vitamin (1, 2, 3).
You can find folate in plant and animal foods like these (1):
Folic acid is added to foods such as flour, ready-to-eat breakfast cereals, and breads (4, 5).
It’s also in dietary supplements, such as multivitamins (1, 4).
Your body uses folate to (1):
Folate deficiency can lead to many health problems, including (1, 2, 6, 7):
Many countries, including the United States, require certain grain products to be fortified with folic acid. Folic acid fortification helps prevent neural tube irregularities in infants (7, 8).
SummaryFolic acid is a synthetic version of the B vitamin folate, which naturally occurs in leafy greens, eggs, and citrus fruits, among other foods. It’s essential to important functions in the body.
The Recommended Dietary Allowance (RDA) for folate is listed in Dietary Folate Equivalents (DFEs). This unit of measure accounts for the differences in how your body absorbs folate from foods and folic acid from fortified foods and supplements.
Your body absorbs natural folate about half as well as folic acid from supplements (1).
Adults need about 400 mcg DFE of folate each day. During pregnancy and breastfeeding, folate needs can increase. The RDA during pregnancy is 600 mcg DFE (1, 6, 7, 9).
Your body stores 15–30 mg of folate. Most of that folate is in your liver, and the rest is in your blood and tissues (1).
The RDA for folate for infants, children, and teens is (1):
SummaryAdults need about 400 mcg DFE of folate each day.
Folate plays essential roles in a baby’s development.
It’s involved in cell division and tissue growth. It also helps the baby’s brain and spine, called the neural tube, develop. Taking folic acid both before and during pregnancy can help prevent neural tube irregularities such as anencephaly and spina bifida (1, 7, 8).
The U.S. Preventive Services Task Force, an independent panel of national disease-prevention experts, recommends that anyone who is trying to become pregnant start taking a daily folic acid supplement containing 400–800 mcg at least 1 month before becoming pregnant and through the first 2–3 months of pregnancy (9).
However, the common recommendation in practice encourages people capable of getting pregnant — of childbearing age and engaging in sexual activity that could result in pregnancy — to take a folic acid supplement, because many pregnancies can be unplanned (6, 7, 9).
Since the 1990s, flour and other foods have been fortified with folic acid. Consuming both fortified foods and folic acid supplements before and during pregnancy can help reduce the risk of neural tube irregularities (5, 7, 8).
Beyond preventing fetal development issues, taking folic acid supplements during pregnancy may improve a child’s mental function and reduce the chance of the child developing autism spectrum disorder (ASD).
However, taking too much folic acid may have a negative effect on a child’s brain development and increase their chances of developing autism, which will be discussed in the next section (29).
Folate is also important for the health of the pregnant person. Supplementing with folic acid has been shown to reduce the risk of pregnancy-related complications, including preeclampsia. Higher folate levels in a pregnant person may lower the risk of preterm birth (10, 30).
Folate is important for the health of both pregnant people and their babies, and it’s not always easy to get enough of this nutrient through your diet alone (6, 7, 9).
SummaryFolic acid supplements help support pregnancy, reduce pregnancy-related complications, and reduce the chance of fetal development issues.
When you take folic acid, your liver has to convert it into the active form, 5-methyltetrahydrofolate (5-MTHF).
If your liver doesn’t convert it quickly enough, folic acid can build up in your blood. Eating foods containing 5-MTHF instead of folic acid can prevent this from happening (1).
Foods that contain 5-MTHF include (1):
Certain gene changes affect how your body uses folate. Methylenetetrahydrofolate reductase (MTHFR) is an enzyme that breaks down homocysteine. Changes called mutations in the code for MTHFR can affect your health by changing folate levels in your body (2).
One of the most common mutations to MTHFR is C677T. People with this variant have less activity of an enzyme that breaks down homocysteine. They may have high levels of homocysteine, which could increase their heart disease risk.
In a pregnant person, this variant can also increase the chance of neural tube irregularities in a developing fetus (2, 31).
There are genetic tests for MTHFR variants, but few people need them.
Having an MTHFR mutation alone doesn’t mean you’re at risk of health problems or that you need treatment. But if your homocysteine levels are high, a healthcare professional may recommend that you take a supplement (31).
SummaryCertain genetic mutations may affect the folate levels in your body.
Eating folate-rich foods and taking natural forms of folate such as 5-MTHF are generally considered safe. But taking high doses of folic acid through supplements could potentially lead to a buildup of unmetabolized folic acid in your blood.
“Unmetabolized” means your body hasn’t broken down the folic acid or converted it into other forms of folate. No confirmed health risks due to unmetabolized folic acid have yet been found, but undiscovered risks may still exist (1, 32, 33, 34, 35).
It’s important to note that most children and adults in the United States get enough folate from food and don’t need to take a folic acid supplement (1).
Taking folic acid during pregnancy helps prevent neural tube irregularities. But having high levels of unmetabolized folic acid in your blood may increase the chance that your child will have ASD.
People who take less than 400 mcg of folic acid daily are unlikely to have high levels of unmetabolized folic acid in their blood (29, 36).
High levels of unmetabolized folic acid during pregnancy may affect children’s mental development.
In a study of 1,682 mother-child pairs, children whose mothers supplemented with more than 1,000 mcg of folic acid per day during pregnancy scored lower on a test of mental abilities than children whose mothers took 400–999 mcg per day (37).
Although these studies suggest there may be risks to taking high doses of folic acid during pregnancy, more research is needed to confirm these findings.
Taking high doses of folic acid may be associated with other health conditions, including the following.
Folic acid might lower the risk of cancers affecting the head and neck, pancreas, esophagus, and bladder. But it may increase the risk of prostate cancer.
So far, research on the topic has not delivered conclusive results, and more studies are needed.
But research suggests that folate may suppress some types of cancer during its early stages, while high doses of folic acid taken after precancerous cells have developed may cause cancer to grow and progress (1, 38, 39).
High dose folic acid supplements may suppress the immune system by reducing the activity of protective immune cells such as natural killer (NK) cells. Whether these immune changes could put people at increased risk of infection is still unknown (40).
SummaryResearch has suggested that high folic acid intake may be associated with certain health conditions, including cancer, autism, and immune system suppression.
Folate and folic acid can be found in many forms. They are added to multinutrient supplements, including multivitamins and B-complex vitamins. Most adult supplements contain 680–1,360 mcg DFE (400–800 mcg of folic acid) (1).
The Tolerable Upper Intake Level (UL) is the highest daily folic acid dose you can take without experiencing harmful side effects.
The UL includes only folate from fortified foods and dietary supplements. High intake of naturally occurring folate from food has not been shown to cause any adverse effects (1).
The UL for folate in supplements and fortified foods is (1, 32):
Age rangeULadults1,000 mcgchildren ages 14–18800 mcgchildren ages 9–13600 mcgchildren ages 4–8400 mcgchildren ages 1–3300 mcgMost children in the United States get enough folate from food, and 30–66% of children ages 1–13 who take folic acid supplements exceed the UL for their age group. Ask a pediatrician before giving your child a folic acid supplement to make sure it’s safe (1).
You can take all forms of folic acid with or without food.
A healthcare professional might recommend a folic acid supplement if you have a deficiency or you are pregnant or thinking about getting pregnant.
Let a healthcare professional know what other prescription and over-the-counter medications you take. Folic acid may interact with some medicines (1).
Store folic acid supplements in a cool, dry place. Keep supplements away from humid areas, such as the bathroom.
There’s no set upper limit for folate in foods. Because folate is water-soluble, your body removes any extra you consume. Still, it may be possible to develop side effects if you take folic acid supplements in amounts greater than the UL (1, 2).
A healthcare professional may recommend higher doses if you have a folate deficiency. Avoid taking more than the UL unless a healthcare professional directs you to do so.
SummaryThe maximum amount of folic acid and folate adults can consume from supplements and fortified foods without experiencing harmful side effects is 1,000 mcg. Children typically get enough folate from food alone.
Folic acid supplements may interact with some commonly prescribed medications, including (1):
If you’re taking one of these medications, ask your doctor before taking folic acid supplements.
SummaryFolic acid supplements may interact with some medications.
Folate supplements are especially important for people who (1, 2):
Avoid giving folate supplements to infants under 1 year old unless a healthcare professional recommends it. Breastmilk, formula, and food should be the only sources of folate in an infant’s diet (1).
SummaryPeople who are pregnant or of childbearing age or who have folate deficiencies often use folic acid supplements.
There are many versions of folate. Folinic acid, folic acid, and 5-methyltetrahydrofolate are the ones most widely used in dietary supplements (1).
Folinic acid is a natural form of folate found in foods. Healthcare professionals call it leucovorin. It’s used to prevent toxic side effects from the drug methotrexate, which is a treatment for some types of cancer (41).
Folinic acid is more effective than folic acid at raising blood folate levels (41).
Some studies have shown that 5-MTHF absorbs better than other forms of synthetic folate. Plus, it’s less likely to interact with medications. This suggests it may be better to take 5-MTHF supplements than folic acid. However, other studies have found no significant differences (42).
SummaryFolinic acid, folic acid, and 5-methyltetrahydrofolate (5-MTHF) are the types of folate most commonly used in dietary supplements.
If you’re considering getting pregnant, it’s recommended that you take a folic acid supplement and eat a diet high in folate. If you think you have a folate deficiency, a healthcare professional can diagnose it and help you get the folate you need.
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