Folic Acid

What is it?

Folic acid is also known as vitamin B9. It is found naturally in leafy green vegetables, where it is known as folate. It is also an additive in some breakfast cereals and bread.

When?

If you are trying to conceive, or are in the first trimester of pregnancy, you’re advised to take folic acid supplements daily.

The general advice is that a dose of 400 micrograms of folic acid per day is sufficient.

But until recently, the advice was to increase to a whopping 5 milligrams daily if your BMI was over 30. That’s more than 12 times the dose! Recent NICE Guidelines (NG247 Maternal and child nutrition) have reversed this.

So what’s going on, and what dose should you be taking?

Why?

Folic acid supplements help the growing fetus’ spine develop properly and reduce the likelihood of a neural tube defect. Neural Tube Defects (NTDs) cause conditions like spina bifida.

It is very unlikely that diet alone would contain enough folic acid to prevent NTDs. So a supplement is recommended for all those in the first trimester of pregnancy or trying to conceive.

Data shows that ‘Overweight women’ (BMI 25.0–29.9 – see the page on BMI for explanation) are more likely – approximately 1.22 times – than ‘normal’ weight (18.5–24.9 BMI) women to have a baby with NTD. ‘Obese women’ (30.0–34.9 BMI) were 1.7 times more likely. ‘Severely obese women’ were 3.11 times more likely to have a baby with NTD.

The overall numbers are low – we’re talking about 1 in 1000 pregnancies. So remember, even if the risk has increased 3x, it’s still a very small risk. It also raises the classic ‘does correlation = causation?’ quandary.

Image shows a seagull sat on a bowed fencing panel under the caption Correlation vs Causation

We can see that having a higher BMI is associated with greater incidence of neural tube defects. Much like in the picture above seagulls are associated with bent fences. But we don’t know if the weight/BMI is the cause of the NTD. Both conditions could be the result of a third issue – or be entirely unconnected… much like the seagull probably isn’t responsible for the damage to the fence.

Reducing Neural Tube Defects

Either way, preventing NTDs is a good idea. Folic acid is seen as a very safe medication, with few side effects, and it’s pretty cheap. Women with a BMI of 27 or above have been found to have lower levels of folate in their blood. Therefore it was deemed ‘worth a try’ to see if extra folic acid could help reduce NTDs in pregnant people with higher BMIs. I mean, it made perfect sense, right?

The RCOG, in suggesting doses of 5mg, looked at results from research on a different group of women. These women were also more likely to have a baby with NTD, having previously had a baby with a NTD. Research on them found that giving them a much higher dose of folic acid (4mg) daily reduced their risk of a future baby developing a NTD by 72%.

So for about 15 years or so, women and birthing people with higher BMIs were given the same raised dose as the women who’d had NTD babies, to see if it helped them too. (Well those who knew about it and could get their doctor/midwife to prescribe it, that is, which was a whole other issue! A 2010 CMACE audit showed that just 2.1% in the UK were taking the 5mg supplement recommended!)

But did it work?

Unfortunately, the evidence since then, while it supports that those in bigger bodies have an increased likelihood of a baby developing a NTD, found that taking the much higher dose of folic acid does not reduce that risk.

Because of this data, NICE reverted the advice given to women and birthing people in larger bodies, back to the standard Folic Acid dose of 400micrograms (400μg).

What is the guidance now?

If you are trying to conceive or in the first 12 weeks of pregnancy, you need to supplement your diet with 400micrograms (400μg) of folic acid. Only those identified by their healthcare professionals for other reasons need take the higher dose – BMI alone does not warrant it.

Fortunately these are very easy and cheap to obtain off the shelf from most supermarkets. Pregnancy multivitamins usually contain the correct dose as standard, so there’s no need to buy separately if you’re also taking these.

Non pregnancy multivitamins are not advised due to the potential of getting too much Vitamin A, which can be harmful.

If you’re already pregnant and in receipt of benefits, you may even be given multivitamins containing the correct balance of vitamins for pregnancy by your midwife.

What about Folic Acid in bread? Didn’t I hear something about that?

Yes! For a number of years this has been discussed as an option to improve public health. From December 2026, this will come into force in the UK.

The government estimates that up to 45% of Uk pregnancies are either unplanned or ‘associated with feelings of ambivalence’. This means that almost half of pregnancies are unlikely to be receiving the 400 microgram recommended dose prior to discovering the pregnancy… and potentially not for the 12 weeks after conception either.

Since Folic Acid has a really low risk profile – it’s safe to give it to everyone, regardless of ability to conceive, so that’s what is going to happen. All flour will have folic acid added to it. https://www.gov.uk/government/news/birth-defects-prevented-by-fortifying-flour-with-folic-acid.