Folate

A B vitamin, best known as the tablet taken in early pregnancy.

People take it for

Pregnancy
Birth weight and growth
Mood
Homocysteine levels
Blood sugar

A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.

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What is folate?

Folate is vitamin B9, one of the nutrients the body cannot make for itself. The word covers the forms found in food; folic acid is the made version, put into supplements and added to flour in many countries. On a shelf it comes either as folic acid or as methylfolate, the form the body can use as it is. Its reputation rests on one use: it has long been routinely prescribed before and in early pregnancy.

Why do people take folate?

Pregnancy

The thinking. For most people this supplement has one moment in life attached to it: before conception and through the first weeks of pregnancy, where it has long been routinely prescribed. The neural tube, which becomes the brain and spinal cord, closes in the fourth week, before most people have had a positive test.

What research has found. Five randomised trials in over 7,000 women, pooled by a Cochrane review, counted the pregnancies affected by a neural tube defect: roughly two-thirds fewer in the folic acid groups, whether or not an earlier pregnancy had been affected. Doses of 400 µg a day did as well as larger ones; miscarriages were no different. This is one of the best-studied uses, and several reviews of trials broadly agree.

Birth weight and growth

The thinking. Plenty of people carry on with folic acid well past twelve weeks, usually inside a pregnancy multivitamin, and ask whether it still does anything. The idea is that a baby whose cells are dividing quickly draws steadily on its mother’s one-carbon supply.

What research has found. A meta-analysis of eight randomised trials found birth weight rose with folate intake, by about two per cent for every doubling, while placental weight and the length of the pregnancy did not shift. In one trial, the children of mothers who had taken methylfolate alone were quicker at an attention task aged eight and a half. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.

Mood

The thinking. Methylfolate has a following among people with low mood, usually taken alongside an antidepressant rather than in place of one. The thinking comes from the methylation cycle: several of the brain’s signalling chemicals need a methyl group, and folate keeps that supply moving.

What research has found. Two reviews came out differently. One pooled eleven randomised trials and found that days or weeks of folate made no difference to depression scores in adults already taking antidepressants, though longer use went with fewer relapses. The other read 23 trials across several mental health conditions, found the most consistent results with the methylated form, and reported it well tolerated. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.

Homocysteine

The thinking. Homocysteine is an amino acid that turns up on blood tests, and folate is what the body uses to turn it back into methionine, so it builds up when folate runs short. People who find a raised reading, often after learning they carry a common variant of the MTHFR gene, take folate to bring it down.

What research has found. In a 13-week trial, 149 adults with moderately raised homocysteine took 200 µg a day and their readings fell by about a fifth; folic acid, methylfolate and a folate-rich diet did much the same. A trial in 69 women with polycystic ovary syndrome found 5 mg a day lowered homocysteine and several markers of inflammation. Research here is still young: a few studies so far, mostly pointing the same way.

Blood sugar

The thinking. This is rarely why anyone starts taking folate, but it is the corner researchers have measured most. A raised homocysteine reading tends to travel with insulin resistance, so trials have asked whether bringing it down with folate moves blood sugar too.

What research has found. Two meta-analyses, covering 29 and 18 randomised trials and more than 20,000 adults between them, with and without diabetes, found small average falls in fasting glucose, fasting insulin and insulin resistance. One reported no clear effect on HbA1c, the three-month blood sugar measure, and in the two trials that counted new cases, type 2 diabetes was no more common. Several reviews of trials have measured this, and they broadly agree.

What does folate do in the body?

Folate’s job is to carry single carbon atoms from one reaction to another. Two of those reactions build DNA: one makes thymidine, one of its four letters, and the other puts together the purines, two more. That is why a shortfall shows first where cells divide fastest, and why a lasting one ends in anaemia.

The other half of the job is methylation. Folate hands a carbon to the enzyme that turns homocysteine back into methionine, a step that also needs vitamin B12, and methionine becomes the body’s main methyl donor, used to mark DNA and to make several signalling chemicals. Supplements join the cycle at different points: folic acid must be converted first, methylfolate is already the form the enzyme takes, and common variants of the MTHFR gene change how briskly that conversion runs.

What do people say about taking folate?

These are anecdotes people have shared, not evidence.

What people like

Very commonly it is reassurance rather than a felt effect: people call it the one supplement they take without question while trying for a baby.
Where a blood test came back low, people often describe palpitations, dizziness or exhaustion easing over about three months on the prescription strength.
A minority on the methylated form describe a very good first week, with more energy and a lift in mood, before it settles.

Common complaints

Very commonly, the frustration is getting the prescription-only 5 mg strength at all: people describe being passed between GP and midwife for weeks.
On the methylated form a minority report headaches, anxiety, irritability or muscle pain, usually after starting on a full dose rather than building up slowly.
Some people cannot tell what the tablet itself did, because pregnancy sickness, coeliac disease or a liver problem could explain what they felt.

How people take it

Most take it inside a pregnancy multivitamin rather than on its own, and only take a single tablet when a doctor asks for the higher strength.
Very commonly people start about three months before trying to conceive and stop at twelve weeks, though a good number carry on to the end.
Those who react badly to the methylated form drop to a very small amount, or take it once or twice a week.

Read from these public discussions:

When to stop taking folic acid? (Mumsnet, 2021)
To stop taking folic acid when TTC? (Mumsnet, 2021)
5 mg folic acid (Mumsnet, 2023)
Folic acid dosage for folate deficiency (Mumsnet, 2024)
5mg folic acid and frustration (Mumsnet, 2024)
Methylfolate side effects (Phoenix Rising forums, 2013)

What forms of folate are there?

Form	What’s different	Per serving, on products we list
Folic acid	The made form, stable and widely used in supplements and fortified food; the body converts it before use.	400 µg
Methylfolate (5-MTHF)	Folate already in the form the body’s methylation enzyme uses, so no conversion step is needed.	400 µg

What else is worth knowing about folate?

Labels give the amount per serving, and a serving may be more than one tablet; folate is measured in micrograms, written µg or mcg.
Doses differed between trials: 200 µg a day for homocysteine, 400 µg and upwards in pregnancy, 1 mg or 5 mg in the polycystic ovary syndrome trials.
The review of 23 trials in mental health reported that folate supplements were well tolerated; the Cochrane pregnancy review found no difference in miscarriages.
Folic acid must be converted before the body can use it, and some circulates unconverted, turning up in cord blood and in infants’ blood; hence the argument between the two forms.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.

The research behind this page (17 studies)

How much does folate cost?

That depends on the form and the pack, so we work out the price of the same dose of every folate product we can find and rank them.

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