Folic acid 400 µg (vitamin B9)

The short version

What it does Taken before and at the very start of a pregnancy, it reduces the risk of neural tube defects in the child — spina bifida, anencephaly. It is the best-rated recommendation in all of preventive medicine concerning a supplement.

What it does not do It serves no purpose if pregnancy does not concern you. It is neither a vitality supplement nor an “energy” product, and there is no reason to take it outside that window.

What the studies say

The US Preventive Services Task Force rates this recommendation grade A, the level reserved for interventions whose net benefit is substantial with high certainty. It is, as far as we know, the only food supplement to reach that grade. The data shows a reduced risk of neural tube defects for periconceptional intake of 0.4 to 0.8 mg a day, and side effects at usual doses are judged minimal.

The window is narrow and that is the whole problem: the neural tube closes before the fourth week of pregnancy, often before a woman knows she is pregnant. Starting when you discover the pregnancy is starting too late. The recommendation does not cover women who have already had an affected pregnancy or those on antiepileptic drugs, who need different doses and medical follow-up.

If you are a woman of childbearing age and you do not rule out a pregnancy within the year, this is eleven euros for three months, and it is the best evidence-to-price ratio in the whole catalogue. If that is not you, walk on by.

How to take it

Relevant for any woman planning a pregnancy or able to become pregnant. Start at least a month before conception, continue through the first trimester. Not applicable outside that situation.

400 µg a day, every day, at a fixed time. One dose, timing does not matter. Many prenatal supplements already contain it: check so you do not double up.

There is nothing to feel, and that is normal: the benefit is about a risk, not a sensation. If you have had a pregnancy affected by a neural tube defect, or take an antiepileptic, talk to your doctor — your dose is not this one.

What is inside

Folic acid, the synthetic form of vitamin B9. It is precisely the form used in the trials behind the recommendation. Methylfolate also exists, an already activated form, sometimes presented as superior.

Prefer classic folic acid dosed at 400 µg: it is the molecule that was tested, and the one every recommendation cites. Methylfolate costs more and has no demonstrated superiority for this indication, outside specific situations to discuss with a doctor.

Megadoses, pointless here: above 1 mg a day, excess folic acid can mask a vitamin B12 deficiency by correcting the anaemia without preventing the nerve damage. And prenatal supplements stacked on top of each other, which quickly exceed the dose.

Cautions

• Previous pregnancy with a neural tube defect: different dose, medical advice
• Antiepileptic medication: medical advice
• Uncorrected vitamin B12 deficiency