What is folic acid, and how much do women need?

What is folic acid used for, and which foods contain it?

Folic acid has one main use in the guidance: helping to prevent neural tube defects, which are conditions of the developing spine and brain such as spina bifida. That is why the advice centers on the months before conception and the early weeks of pregnancy.

On the plate, natural folate comes from leafy greens and beans. Folic acid reaches food by being added to it, so fortified foods are where to find it: enriched cereal grain products in the US, and fortified breakfast cereals in the UK.

How much is added depends on where you live. US enriched cereal grain products have been required to contain folic acid since 1998, at 140 µg per 100 g, while in the UK mandatory fortification of non-wholemeal wheat flour is due from December 2026, at 250 µg (0.25 mg) per 100 g.

Food is a helpful base, not the whole plan. Guidance in both countries still names a daily folic acid supplement for anyone who could become pregnant, with folate-rich foods alongside it.

What does the evidence say about folic acid?

The reassuring part is how consistent the evidence is. Folic acid taken before and in early pregnancy helps prevent neural tube defects, and the US Preventive Services Task Force (USPSTF) recommends 400–800 µg a day for anyone planning a pregnancy or who could become pregnant.

The CDC gives matching advice in plainer terms: 400 µg of folic acid every day. Both are addressed to anyone who could become pregnant, not only to women who are actively trying, because the recommended window opens before conception. UK guidance from NICE and the NHS rests on the same finding.

The clearest picture of what folic acid does across a whole country comes from one CDC report, published in 2015. It looked at spina bifida and anencephaly before and after folic acid went into US grain products. After fortification, the two conditions became 28% less common.

The CDC also put that change into births. It estimates that fortification means about 1,326 fewer births affected by a neural tube defect in the US each year. For the UK, GOV.UK expects flour fortification to reduce neural tube defects by about 20%.

A recommendation written for individual women and a fall measured across a whole country point the same way. If you have only just started thinking about folic acid, or a pregnancy has arrived sooner than planned, that is common. It's worth beginning from where you are, and a GP, midwife or doctor can help with the timing.

How much folic acid should you take, and when?

A sensible target is 400 µg of folic acid a day. US guidance allows a range of 400–800 µg, while the NHS in the UK names a single 400 µg supplement, ideally begun 3 months before pregnancy and continued until 12 weeks.

A higher prescribed dose is used after a pregnancy affected by a neural tube defect: in the US the CDC gives 4,000 µg a day, starting 1 month before pregnancy and continuing through the first 3 months, and in the UK the NHS gives 5 mg a day until 12 weeks. UK advice from NICE PH11 and the NHS also offers that higher dose to women with diabetes, women taking epilepsy medicines and women with a BMI of 30 or more, groups the US line does not list. In both countries it starts with a conversation with a doctor, so if any of these apply to you, it's a fair question to raise.

Folic acid supplements come on their own or as part of a broader product. Many women choose prenatal vitamins while trying. A useful one contains folic acid, iodine (150 µg) and vitamin D. The NICE and NHS guidance on pregnancy vitamins steers away from high-dose vitamin A (retinol) supplements in pregnancy, so it's worth a glance at the label for that too.

Labels can look different on each side of the Atlantic. US labels usually print mcg and UK labels spell out micrograms; they are the same unit, written µg on this page.

What did the studies do, and what did they not show?

The CDC report was a before-and-after comparison. It set 1995–96, before fortification, against 1999–2011, after it. In the programs that also record cases identified before birth, the fall was 35%, larger than the overall figure.

That kind of study describes a country. It cannot follow one woman and say what a tablet did for her. It also measured folic acid in food, not folic acid supplementation chosen by an individual, so the fortification numbers and the daily-supplement advice are two separate strands of evidence.

The UK figure is a forecast, not a measured result. A measured one can only come once fortified flour has been on the shelves for some years.

The USPSTF recommendation covers one outcome, preventing neural tube defects. Questions it does not settle, such as whether a higher dose suits a particular health condition, are individual ones, better taken to a doctor than to population data.

Next steps

A good place to start is the label on any supplement you already have, to see whether it lists folic acid and how many micrograms it gives. If you are trying to conceive, or pregnancy is possible, a GP, midwife or doctor can help you settle on a dose and a start date, and can tell you whether a higher dose applies to you. Some women prefer a stand-alone tablet, others a prenatal vitamin, and many count on fortified foods as well. What works for one woman may not suit another, so this is not one size fits all, and the choice that fits your life and your health is yours to make.