Pregnant women should not be alarmed by a new study linking excessive folate consumption and a higher risk of the child developing autism say scientists, who have labelled the findings "irresponsible" and "probably a load of rubbish".
Currently expectant mothers in Australia are advised to consume at least 600 micrograms of folate daily, through folate-rich foods and taking the synthetic version, folic acid, as a supplement. That's because research has shown folate reduces the chance of spina bifida and other - sometimes fatal - birth defects.
But a new study due to be presented at the International Meeting for Autism Research in Baltimore on Friday suggests that if a mother had four times the “adequate” level of folate just after giving birth, the risk the child would develop a disorder on the autism spectrum doubled.
The authors from Bloomberg School of Public Health at Johns Hopkins University also said very high levels of vitamin B12 (involved in processing folate) in new mothers could triple the risk of autism or a similar condition. And if both folate and vitamin B12 were high, the risk increased 17.6 times.
Other scientists have cast doubt on the findings, which were promoted in a press release ahead of the conference.
They warn the study has not been fully peer-reviewed, and because the results are inconsistent with previous research, that's a really important aspect.
"This would be an extraordinary finding. It would therefore require extraordinary evidence," says Dr Max Davie, Mental Health lead at Britain's Royal College of Paediatrics and Child Health.
"This study only shows an association, which may be due to chance, reverse causation, or a common unknown factor causing both an increase in ASD diagnosis, and B12/folate levels," says Davie. "The authors are going way out on a limb in drawing causal connections here, and are being quite irresponsible in undermining decades of public health work."
Professor Colin Binns from the School of Public Health at Curtin University in Perth, says pregnant women should not be concerned by the study, as the benefits of folate are well-established.
"They shouldn't be alarmed because it's probably a load of rubbish - it's just nonsense," Binns tells SBS Science.
"Biologically we know that a deficiency of folate causes neural tube defects - that's well and truly proven. The same studies didn't show that there was any association between autism and neural tube defects, which you'd expect if folate was involved.
"[I want to] reassure the mothers of Australia that taking folate supplements is excessively safe, it's in the interests of their health and their baby's health that they should continue to do so. The last thing we want to happen is... to see an increase in cases of spina bifida and anencephaly (a fatal condition when the baby is born without a brain)."
Continue taking folate
Since 2009 all wheat flour used for bread making in Australia must contain folic acid, which means most bread sold in Australia (except organic bread) is fortified with folic acid. Breakfast cereals and fruit juices may also have added folic acid.
Professor Carol Bower from the Telethon Kids Institute helped campaign for mandatory folate fortification in bread after her research with Professor Fiona Stanley helped confirm the link between inadequate levels of folate and neural tube defects.
Bower said women should continue to strive for a sufficient intake of folate from around the time of conception through the first 12 weeks of pregnancy.
"Without access to more information from the study, it is not possible to know how likely it is that these findings support a causative association between folate, B12 and autism. In contrast, the evidence for folate preventing neural tube defects is solid."
The study did not find a causal link showing how folic acid might cause autism, but was based on an apparent correlation between high folate in mothers and rates of autism among their children.
The Johns Hopkins researchers stressed they were not suggesting that it was a bad idea to take folic acid supplements, but that "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," said the study's lead author Ramkripa Raghavan. "What we need to figure out now is whether there should be additional recommendations about just what an optimal dose is throughout pregnancy.”