Why pregnant women should avoid taking folic acid

Pregnant women who take too much folic acid and its natural form vitamin B12 could increase the risk of their baby developing autism by 17 times, warns new research.

Mums-to-be are often told to take folic acid supplements, as too little folate is bad for the development of the brains and nervous systems of babies.

Deficiencies have been linked to birth defects and an increased risk of autism.

But the new study suggests that it is possible to take too much of the supplement.

Folate, also known as vitamin B12, is found in fruit and veg, while the synthetic version, folic acid, is used to fortify cereals and breads.

The new research suggests that mums who take more than four times the amount of folate than is considered adequate double the risk of their child developing autism.

Very high levels trebled the risk of babies developing autism, the study found

Very high vitamin B12 levels were found to treble the risk of babies developing the disorder.

And, if both levels of supplements were extremely high, mums could increase the risk by 17.6 times.

The study involved 1,391 mother and baby pairs who were part of the Boston Birth Cohort in the United States.

Blood folate levels were taken from the mothers shortly after they had given birth.

The researchers found that one in 10 of the women had what was considered to be an excess amount of folate, while six per cent had an excess amount of vitamin B12.

The majority of the mothers in the study said they had taken multivitamins, which would include folic acid and vitamin B12, throughout pregnancy.

GettyFolate, BroccoliFolic acid occurs naturally in foods such as broccoli

While researchers didn't know why some of the women had such high levels of folic acid, it could be down to consuming too many foods rich in the vitamin or supplements.

They also said some women could be genetically predisposed to absorbing greater quantities of folate, metabolising it at a slower pace, or a combination of the two.

While it is the case that many vitamin supplements that the body flushes out the excess, this may not be the case with vitamin B12 and folic acid.

Study author Ramkripa Raghavan, a doctor of public health candidate at Johns Hopkins University in the US, said: "This research suggests that this could be the case of too much of a good thing.

"We tell women to be sure to get folate early in pregnancy.

Some women could be predisposed to absorbing greater quantities of folate

"What we need to figure out now is whether there should be additional recommendations about just what an optimal dose is throughout pregnancy."

Despite the findings, researchers stress that pregnant women shouldn't reject supplements.

A recent UK study found that just a third of women report taking folic acid before falling pregnant.

Dr Margaret Daniele Fallin, of Johns Hopkins, said: "Adequate supplementation is protective, that's still the story with folic acid.

"We have long known that a folate deficiency in pregnant mothers is detrimental to her child's development. But what this tells us is that excessive amounts may also cause harm. We must aim for optimal levels of this important nutrient."

The findings are due to be presented at the International Meeting for Autism Research in Baltimore.