Mothers who have elevated blood levels of vitamin B12 (cobalamin) or B9 (folate) during pregnancy are more likely to have autistic children.
Folic acid is a B vitamin and synthetic form of folate used in nutritional supplements, breads and fortified foods.
Dark green leafy vegetables are high in folate while vitamin B12 is naturally present in foods from animal sources such as meat, dairy, and eggs.
Folate and B12 are important for the foetus to develop as a deficiency in pregnant mums would put her future child at a greater risk of anaemia and neural tube defects such as spina bifida.
However, high levels of folate (four times higher than the normal range) during pregnancy could triple the risk of Autism Spectrum Disorder (ASD) in new born babies, a study has found.
Similarly, excessive amounts of vitamin B12 in mums triples the risk of ASD for their new babies.
The risk of developing ASD can rise by 17.6 times if both B12 and folate levels are very high.
According to the guidelines, women during pregnancy and before getting pregnant should take 400 micrograms (mcg) of folic acid daily to avoid birth defects.
However, maternal multivitamin supplementation and fortified food intake requires careful planning as increased folate and B12 levels could be associated with ASD.
Professor M. Daniele Fallin, the study co-author, 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.”
Despite the importance of folate and B12, still one quarter of women of reproductive age in the United States are deficient.
Both low and high levels of folate were linked to autism, a neurodevelopmental disorder, the signs of which include repetitive or unusual behaviour, social impairment, and abnormal communication.
In this study, six percent of pregnant women had high blood levels of vitamin B12 (more than 600 picomoles per litre) and 10 percent were high in folate (more than 59 nanomoles per litre).
According to the World Health Organisation, a normal range for folate is between 13.5 and 45.3 nanomoles per litre during the first trimester of pregnancy.
A normal range for folate is between 13.5 and 45.3 nanomoles per litre during the first trimester of pregnancy but there is no established range for vitamin B12 yet.
The researchers think high consumption of folic acid-fortified foods and taking too many supplements could be the reason that some participants had such elevated levels in their blood.
The study was published in the journal Paediatric and Perinatal Epidemiology (Raghavan et al., 2018).