Folic Acid (Vitamin B9): Benefits, Uses, Sources & Side Effects

Folic Acid (Vitamin B9): Benefits, Uses, Sources & Side Effects

Folic acid is the synthetic form of the naturally occurring vitamin folate, also known as vitamin B9. Folate is found in food while folic acid is used in supplements and added to fortified foods like bread, pasta, and cereal.

Folate is an essential B vitamin that helps your body make DNA and helps your cells divide to create new cells. Folic acid supplementation can help treat folate deficiencies and help promote healthy neural tube development (the early formation of the spine and brain) during pregnancy.

Benefits of Folic Acid 

Folate from food converts to its active form, 5-methyltetrahydrofolate (5-MTHF), in the digestive tract. Folic acid has to enter the bloodstream, liver, and other tissues to convert to 5-MTHF. This may seem inefficient, but the body can easily absorb folic acid. As a result, folic acid supplements can help increase blood folate levels to treat and prevent certain conditions.

Prevents Neural Tube Defects During Pregnancy

Healthcare providers recommend pregnant people and people who can become pregnant take folic acid to help reduce the risk of neural tube defects in the fetus. Neural tube defects affect the formation of the brain, spine, or spinal cord. The most common defects include spina bifida (an underdeveloped spine) and anencephaly (missing parts of the brain and skull).

Taking 400 micrograms (mcg) of folic acid daily can help reduce the risk of neural tube defects.

In 1998, the United States started adding folic acid to fortified foods to help reduce neural tube defects. Studies have shown from 1998 to 2011 the food fortification program helped reduce neural tube defect rates by 28%. Additional research has found fortifying food with folic acid has continued to help prevent neural tube defects.

Treats Folate Deficiency Conditions

A folate deficiency is rare, but certain health conditions can affect how people absorb folate. People with ulcerative colitis, inflammatory bowel disease, and kidney dysfunction often develop folate deficiencies. To prevent or treat a folate deficiency, people with these conditions can take folic acid to help replenish their folate levels.

A folate deficiency can also cause megaloblastic anemia, which causes bone marrow to produce unusually large and immature red blood cells. Taking folic acid can help treat this type of anemia and relieve symptoms like fatigue, shortness of breath, heart palpitations, and mouth sores.

People deficient in folate and other B vitamins may also develop hyperhomocysteinemia, which causes too much of the amino acid homocysteine in your blood. People with kidney disease and genetic disorders affecting how their body produces 5-MTHF are more likely to develop the condition. Taking folic acid can help treat the condition.

Slows Age-Related Macular Degeneration

Taking high doses of folic acid may help slow the progression of age-related macular degeneration. This eye disorder leads to central vision loss, and people 65 and older are more likely to develop the condition.

Research shows that taking B vitamins, including B6, folate, and B12, can help regulate potential risk factors for developing age-related macular degeneration, like homocysteine levels and hyperhomocysteinemia.

Research has found high-dose folic acid was more effective at slowing down progression than thiamine (vitamin B1) and riboflavin (vitamin B2), which are often used to help treat macular degeneration.

A study including 2,525 participants found combining folic acid and vitamin B12 helped slow age-related macular degeneration. After 13 years of supplementation, only 405 participants progressed to the late stage of age-related macular degeneration.

Other studies have also found people who had higher intakes of folate and vitamin B6 had a lower risk of advanced macular degeneration. However, these studies mainly included populations that had food fortified with folic acid, which may skew the amount of folic acid some participants got from food.

Reduces the Risk of Stroke

Folic acid can help lower homocysteine levels, and elevated homocysteine levels are associated with an increased risk of stroke. Research shows taking folic acid may help prevent stroke, especially in countries that do not have folic acid fortification programs that add folic acid to foods.

A review of research including over 65,000 people looked at the effect of folic acid supplementation for people with a risk of stroke in countries without food fortification programs. The researchers found folic acid supplementation reduced the risk of stroke by 15% for people in these areas.

The researchers noted countries with food fortification programs like Canada and the U.S. did not see improvements in stroke risk reduction from additional folic acid supplementation.

A large study in China also found adults with hypertension (high blood pressure) who took folic acid and enalapril (a high blood pressure medication) for 4.5 years reduced stroke by 21%. This was more effective than just taking enalapril. China does not have a folic acid fortification program, so it’s unlikely participants consumed additional folic acid from food.

Good Sources of Folic Acid

Unlike folate, folic acid is not naturally found in food since it’s the synthetic form of the B vitamin. However, folic acid is often added to fortified foods—or foods labeled as “enriched” that have added vitamins and minerals.

Enriched foods typically include grain products like bread, pasta, and cereals. Folic acid is more stable than folate when added to cooked foods because it doesn’t break down as easily by heat.

Enriched foods with added folic acid often include grain products like:

  • White bread: 50 mcg per slice, or 13% of the Daily Value (DV)
  • Cooked white rice: 90 mcg per ½ cup, or 25% of the DV
  • Cereal: 100 mcg per ½ cup, or 25% of the DV
  • Cooked spaghetti: 74 mcg per ½ cup, or 19% of the DV

Legumes, dark leafy greens, and citrus fruits naturally contain folate. Foods that offer folate include:

  • Cooked lentils: 358 mcg per cup, or 90% of your daily value (DV)
  • Cooked beef liver: 212 mcg per 3 ounces, or 54% of the DV
  • Beets: 148 mcg per cup, or 37% of the DV 
  • Cooked asparagus: 134 mcg per ½ cup, or 34% of the DV
  • Cooked kidney beans: 131 mcg per cup, or 33% of the DV
  • Cooked broccoli: 84 mcg per ½ cup, or 21% of the DV 
  • Avocado: 82 mcg per ½ avocado, or 21% of the DV
  • Orange: 55 mcg per large fruit, or 14% of the DV 
  • Spinach: 58.2 mcg per cup, or 14% of the DV 
  • Papaya: 53 mcg per cup, or 13% of the DV
  • Cooked Brussels sprouts: 47 mcg per ½ cup, or 12% of the DV

How to Take Folic Acid

Folic acid supplements are available over-the-counter as capsules, tablets, soft gels, and gummies. Folic acid is also added to multivitamins, prenatal vitamins, and B-complex supplements.

Folic acid can be taken with or without food in the morning. However, the body absorbs folic acid more efficiently on an empty stomach. When you take folic acid with food, the body only absorbs about 85% of folic acid into the bloodstream. The body absorbs almost 100% of the folic acid when you take it without food.


The recommended dosage of folic acid depends on your age and if you are pregnant or breastfeeding. Adult supplements range from 400-800 mcg of folic acid and children’s multivitamins range from 200-400 mcg of folic acid.

People who are pregnant or could become pregnant should take 400-800 mcg of folic acid per day. If you have a family history of spina bifida and are pregnant or plan to become pregnant, your healthcare provider may prescribe up to 4,000 mcg of folic acid per day.

If you have a folate deficiency, people often feel better 24 hours after taking folic acid. However, it can take several months for enough folate to build up in your blood to help prevent neural tube defects.

The Recommended Dietary Allowances (RDAs) for folate include:

  • Birth to 6 months: 65 mcg dietary folate equivalent (DFE) from breastmilk or formula
  • 7-12 months: 80 mcg DFE from breastmilk or formula
  • 1-3 years: 150 mcg DFE
  • 4-8 years: 200 mcg DFE
  • 9-13 years: 300 mcg DFE
  • 14-18 years: 400 mcg 
  • 19+ years: 400 mcg DFE
  • Pregnant: 600 mcg DFE
  • Breastfeeding: 500 mcg DFE

What are DFEs?

Dietary folate equivalents (DFEs) are used to measure folate to show bioavailability—or how much of the nutrient is absorbed by the body.

  • 1 mcg DFE equals 1 mcg of food folate 
  • 1 mcg DFE equals 0.6 mcg folic acid from fortified foods or supplements taken with food
  • 1 mcg DFE equals 0.5 mcg folic acid from dietary supplements taken without food

Is Folic Acid Safe?

Folic acid is generally considered safe in adults and pregnant people. Still, taking doses over 1,000 mcg may lead to side effects, and some people can have hypersensitive reactions. Before taking any folic acid supplement, discuss the correct dosage with your healthcare provider. You may need to take more than 1,000 mcg if you are pregnant and have a family history of spina bifida.

Potential Drug Interactions

Folic acid can interact with certain medications, causing folate deficiencies or decreasing effectiveness of the drug. If you take the following medications, talk to your healthcare provider before taking folic acid supplements:

  • Methotrexate: This folate antagonist helps kill cancer cells by preventing cells from using folic acid to make DNA. Supplementing folic acid may reduce the anti-cancer effects of Rheumatrex and Trexall (methotrexate) when used to treat cancer. 
  • Anti-epileptic: Medications like Dilantin (phenytoin), Carbatrol (carbamazepine), and Depacon (valproate) can reduce folate levels in the blood. Taking folic acid with these medications may also lower medication levels in the blood. 
  • Sulfasalazine: The ulcerative colitis medication Azulfidine (sulfasalazine) decreases how much folic acid the intestines absorb and may cause a folate deficiency. 

What to Look For  

You can find folic acid supplements (alone or combined into prenatal and multivitamins) over the counter at drugstores, health foods stores, supplement stores, and grocery stores. Your healthcare provider may also prescribe you a supplement for higher doses of folic acid. 

The U.S. Food and Drug Administration does not approve dietary supplement claims and labeling before they hit stores. As a result, vitamin supplements can vary in quality. To ensure you’re purchasing a safe and quality folic acid supplement, choose products tested and certified by independent labs like U.S. Pharmacopeia, ConsumerLab, or NSF International.

Can You Take Too Much Folic Acid?

You can take too much folic acid, and you may experience uncomfortable side effects if you take more than the tolerable upper intake level (UL). Generally, adults and pregnant people should avoid taking more than 1,000 mcg.

However, your healthcare provider may recommend a higher dose if you are pregnant or have a folate deficiency. The ULs for folic acid supplements and fortified foods include:

  • 1-3 years: 300 mcg
  • 4-8 years: 400 mcg
  • 9-13 years: 600 mcg
  • 14-18 years: 800 mcg
  • 19+ years: 1,000 mcg
  • Pregnant or lactating (14-18 years): 800 mcg
  • Pregnant or lactating (19+): 1,000 mcg

Some researchers also believe taking too much folic acid may cause an imbalance in B vitamins and hide symptoms of a dangerous vitamin B12 deficiency. Additionally, research has linked high folic acid doses to an increased risk of colorectal and prostate cancer. However, more research is needed to prove the link.

Side Effects of Folic Acid

People rarely experience side effects from folic acid supplements. However, taking folic acid doses over 1,000 mcg can cause side effects like:

  • Upset stomach
  • Nausea
  • Diarrhea
  • Insomnia (trouble sleeping)
  • Skin rashes

While rare, some people can have hypersensitive reactions to folic acid, including rash, itching, and difficulty breathing. It is also possible to have a life-threatening reaction that leads to anaphylactic shock.

A Quick Review

Folic acid is a synthetic form of folate typically taken to help prevent neural tube defects during pregnancy. The B vitamin is also added to fortified foods like bread and cereal to help prevent neural tube defects. Taking folic acid can also help treat folate deficiencies, and it may help reduce your risk of stroke and slow down age-related macular degeneration. Before taking folic acid, check with your healthcare provider. 


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