Folate and Folic Acid: Pregnancy, Reference Intakes and Upper Limits

Nutrition · Published 2026-10-24

Brown, red and black lentils laid out in three stripes on a grey surface — Three kinds of lentils, side by side.

Folic acid before and in early pregnancy is one of the clearest success stories in nutrition: trials showed it prevents most neural tube defects, and countries that fortify flour have seen rates fall. Outside pregnancy, the story is quieter, and there is an upper limit worth knowing.

Folate and folic acid are not the same thing

Folate is the general name for a group of B vitamins (vitamin B9) found naturally in foods such as dark green leafy vegetables, Brussels sprouts, broccoli, peas, chickpeas, beans, lentils, oranges and liver. Folic acid is the synthetic form used in supplements and fortified foods. It is more stable than food folate and better absorbed, which is why intake values are expressed in dietary folate equivalents (DFE):

1 mcg of food folate = 1 mcg DFE;
1 mcg of folic acid taken with food = 1.7 mcg DFE;
1 mcg of folic acid taken on an empty stomach = 2 mcg DFE.

Folate is needed to make DNA and for cell division, which is why it matters so much when cells divide fast: in the early embryo and in the bone marrow that makes red blood cells. Deficiency causes megaloblastic anaemia, the same type caused by B12 deficiency.

Reference intakes

Body	Adults	Pregnancy	Breastfeeding
US National Academies (NIH ODS)	RDA 400 mcg DFE	600 mcg DFE	500 mcg DFE
EFSA (EU)	PRI 330 mcg DFE	AI 600 mcg DFE	AI 500 mcg DFE
UK reference nutrient intake	200 mcg	Plus 400 mcg folic acid supplement before conception and to week 12

These are intakes for the general population. The pregnancy recommendation below is separate: it concerns a supplement taken in addition to a normal diet, because food alone rarely provides enough folate early enough.

Folic acid and neural tube defects

Neural tube defects are serious birth defects of the brain and spinal cord, such as spina bifida and anencephaly. The neural tube closes within the first four weeks after conception, often before a person knows they are pregnant. Randomised trials in the 1990s, notably the UK Medical Research Council vitamin study published in 1991, showed that folic acid taken around conception sharply reduced the risk of a recurrence.

A Cochrane review pooling the trials found that periconceptional folic acid supplementation reduced the risk of neural tube defects by about 70% (risk ratio 0.31) compared with no folic acid or placebo (De-Regil et al., 2015).

The resulting recommendations are consistent across authorities:

NHS: take a 400 microgram folic acid supplement every day from before you are pregnant (ideally while trying to conceive) until you are 12 weeks pregnant.
Higher dose for higher risk: the NHS says some people are prescribed 5 milligrams (5,000 mcg) a day instead, for example if they or their partner have a neural tube defect, have had a previous pregnancy affected by one, have a family history of one, have diabetes, take certain anti-epilepsy medicines, have a body mass index of 30 or more, or have sickle cell disease or thalassaemia. This dose is prescribed by a doctor; it is not a self-care choice.
US Preventive Services Task Force (2023): recommends a daily supplement containing 0.4 to 0.8 mg (400–800 mcg) of folic acid for all persons planning to or who could become pregnant.

Because about half of pregnancies are unplanned in many countries, the US and others recommend folic acid to anyone who could become pregnant, not only to people actively trying.

Fortification

Since supplement advice alone misses many unplanned pregnancies, more than 80 countries require folic acid to be added to flour or other staples. The United States has required it in enriched grain products since 1998, and Canada since the same year; both saw neural tube defect rates fall afterwards. The UK government has legislated to add folic acid to non-wholemeal wheat flour, with the requirement scheduled to apply from late 2026. Fortification does not replace the advice to take a supplement before and during early pregnancy.

Who else may be short of folate

People with a low intake of vegetables, pulses and fortified foods.
People with heavy alcohol use, which reduces folate absorption and increases losses.
People with malabsorption conditions such as coeliac disease or inflammatory bowel disease.
People taking medicines that interfere with folate, such as methotrexate, some anti-epileptic drugs and sulfasalazine. In these cases folic acid may be prescribed, and timing matters, so it should be managed by the prescriber.

The upper limit

The US tolerable upper intake level for adults is 1,000 mcg a day of folic acid from supplements and fortified foods; EFSA set the same figure. The limit does not apply to folate naturally present in food, which is not associated with harm. It was set mainly because high folic acid intakes can correct the anaemia of vitamin B12 deficiency while nerve damage continues unnoticed. Questions about other effects of high folic acid intakes (for example on cancer progression) have been studied, but the evidence is inconsistent and has not led authorities to change the limit. The 5 mg pregnancy dose exceeds the upper limit and is therefore given under medical supervision, for a defined period, after weighing benefits and risks.

Do folic acid supplements help other conditions?

Folic acid lowers blood homocysteine, and high homocysteine is associated with cardiovascular disease. However, large trials of B-vitamin therapy in people with existing vascular disease did not show a convincing reduction in heart attacks overall. Some trials in populations without folic acid fortification, such as the China Stroke Primary Prevention Trial (2015), found a reduction in first stroke among adults with high blood pressure taking enalapril plus folic acid, but this result may not apply to populations where flour is already fortified. Folic acid is not a general cardiovascular preventive in fortified countries.

In short

Folate is the natural form; folic acid is the synthetic form in supplements and fortified foods.
Anyone who could become pregnant is advised to take 400 mcg of folic acid a day before conception and until week 12 (US: 400–800 mcg).
Higher-risk people may be prescribed 5 mg; this is a medical decision.
The adult upper limit is 1,000 mcg a day of folic acid, mainly to avoid masking B12 deficiency.

This page is general information, not medical advice. If you are planning a pregnancy, are pregnant or take medicines that affect folate, ask your GP, midwife or pharmacist which folic acid dose is right for you.

Sources

NIH Office of Dietary Supplements, Folate fact sheet for health professionals.
NHS, Vitamins, supplements and nutrition in pregnancy.
De-Regil LM et al. Effects and safety of periconceptional oral folate supplementation for preventing birth defects. Cochrane Database Syst Rev 2015.
US Preventive Services Task Force. Folic acid supplementation to prevent neural tube defects: recommendation statement. 2023.
EFSA, Dietary reference values finder.