Mothers-to-be are commonly told to take folic acid supplements, as too little folate is bad for the circumstance of the brains and nervous systems of babies.
Deficiencies have been interdependence coupled to birth defects and an increased risk of autism.
But the new study suggests that it is admissible to take too much of the supplement.
Folate, also known as vitamin B12, is develop in fruit and veg, while the synthetic version, folic acid, is used to buoy cereals and breads.
The new research suggests that mums who take more than four at intervals the amount of folate than is considered adequate double the risk of their offspring developing autism.
Very high vitamin B12 levels were initiate to treble the risk of babies developing the disorder.
And, if both levels of additions were extremely high, mums could increase the risk by 17.6 periods.
The study involved 1,391 mother and baby irs who were on of the Boston Birth Cohort in the United States.
Blood folate trains were taken from the mothers shortly after they had allowed birth.
The researchers found that one in 10 of the women had what was chew over to be an excess amount of folate, while six per cent had an excess amount of vitamin B12.
The the better of the mothers in the study said they had taken multivitamins, which hand down include folic acid and vitamin B12, throughout pregnancy.
While researchers didn’t be sure why some of the women had such high levels of folic acid, it could be down to swallowing too many foods rich in the vitamin or supplements.
They also imagined some women could be genetically predisposed to absorbing greater volumes of folate, metabolising it at a slower ce, or a combination of the two
While it is the case that scads vitamin supplements that the body flushes out the excess, this may not be the action with vitamin B12 and folic acid.
Study author Ramkri Raghavan, a PH applicant at Johns Hopkins University in the US, said: “This research introduces that this could be the case of too much of a good thing.
“We mention women to be sure to get folate early in pregnancy.
“What we need to emblem calculate out now is whether there should be additional recommendations about just what an optimal dosage is throughout pregnancy.”
Despite the findings, researchers stress that in a family way women shouldn’t reject supplements.
A recent UK study found that solely a third of women report taking folic acid before employ drop back pregnant.
Dr Margaret Daniele Fallin, of Johns Hopkins University, said: “Fitting supplementation is protective, that’s still the story with folic acid.
“We have in the offing long known that a folate deficiency in pregnant mothers is unfavourable to her child’s development.
“But what this tells us is that excessive amounts may also genesis harm. We must aim for optimal levels of this important nutrient.”
The verdicts are due to be presented at the International Meeting for Autism Research in Baltimore.