Folic acid

Studies in people

• Open question

  Autism risk in children²

  Many people with autism seem to get too little folic acid, but scientists still need better studies to know more.

• Concern

  Vitamin B12 deficiency³

  Folic acid may hide a B12 shortage and speed up nerve damage, but scientists have not yet proved this.

• Benefit

  Birth defects in babies⁴

  Folic acid taken before and during pregnancy may lower the chance of some birth defects.

• Concern

  Chemo treatment side effects⁵

  In people having capecitabine chemotherapy, taking folic acid supplements was linked to more treatment side effects.

• Benefit

  Ovarian reserve in women⁶

  In women getting fertility treatment, folic acid from food and supplements was linked to a slightly higher egg count.

• Benefit

  Birth defects prevention⁷

  Folic acid in fortified flour helps prevent birth defects, and experts found no proven risks at current levels.

• No harm found

  Asthma risk in children⁸

  Folic acid in pregnancy was once feared to raise asthma risk, but human studies do not back that up.

• Benefit

  Heart defects in babies¹³

  In this study, women who took folic acid before pregnancy had fewer babies born with heart defects.

• Benefit

  B vitamin blood levels¹⁵

  Folic acid supplements raised folate levels in vegans and vegetarians, and low folate was rare in this study.

• Benefit

  Early birth risk¹⁷

  Pregnant women who took folic acid for over 12 weeks had fewer early births.

• Open question

  Twin pregnancies¹⁸

  Taking folic acid before pregnancy was first linked to twins, but that link disappeared once IVF was accounted for.

• Benefit

  Pregnancy blood pressure risk²⁰

  In pregnant women, taking folic acid supplements was linked to a lower risk of preeclampsia.

• Open question

  Worry and overthinking²¹

  People who ate more folate tended to worry less, but scientists do not yet know whether folic acid causes this.

Study type not stated

• Concern

  B12 deficiency effects²³

  Folic acid may make the brain and metabolic problems caused by low B12 worse, though scientists do not yet know for sure.

• Concern

  Cancer risk and pregnancy²⁴

  Too much folic acid may raise cancer risk and affect pregnancy, but this is not yet certain.

How it’s made and used

• Supplement timing in pregnancy⁹

  Most pregnant women in this study took folic acid too late, and many had low folate.

• Preterm birth risk¹⁰

  In babies with spina bifida, preterm birth was more likely when mothers took no folic acid and ate little folate.

• Foods with added vitamins¹¹

  Many foods in Warsaw shops had folic acid added, but most shoppers knew little about it.

• Weight and blood vitamin levels¹²

  People who are overweight or obese tend to have lower folate levels in their blood than people of normal weight.

• Chances of getting pregnant¹⁴

  In 9,559 women trying to conceive, eating less food folate was linked to lower chances of getting pregnant each cycle.

• Pregnancy vitamin intake¹⁶

  Most pregnant women in this study got enough folic acid, but many took in more than the recommended upper limit.

• Fortified flour and blood¹⁹

  In Brazilian adults, eating more folic acid from fortified flour was linked to higher unmetabolized folic acid in the blood.

• Liver conversion of vitamins²²

  Folic acid must be turned into its active form by the liver before the body can use it.

• Fortified food nutrient accuracy²⁵

  In Canadian fortified foods, folic acid was often higher than the amounts listed.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.