While the current study cannot establish a cause-and-effect relationship, the team behind the publication say it does raise questions about the association and warrants further investigation.
Led by Dr Elizabeth DeVilbiss from the department of epidemiology and biostatistics at Drexel University, the team analysed data from more than 270,000 mother and child pairs living in Sweden.
After adjusting for several potentially confounding factors in both mothers and children, the team reported that multivitamin use, with or without additional iron and/or folic acid, was associated with a lower likelihood of child ASD with intellectual disability relative to mothers who did not use folic acid, iron, and multivitamins.
“We observed a potential inverse association between maternal multivitamin supplement use and ASD with intellectual disability in offspring,” concluded the team – who noted that among many remaining questions is whether the association is specific to autism or whether it reflects the risk of intellectual disability that needs to be explored in future research.
“Given the current understanding and strength of evidence supporting the importance of nutritional supplementation during pregnancy, these results on their own should not change current practice,” they said.
“Still, these findings raise questions that warrant investigation,” added DeVilbiss and colleagues – noting that a ‘sufficient’ body of mechanistic evidence supporting the finding does not yet exist.
Autism spectrum disorder (ASD) includes a range of conditions, including Asperger syndrome, that affect a person's social interaction, communication, interests and behaviour.
It's estimated that about 1 in every 100 people in the UK has ASD – with more boys diagnosed with the condition than girls.
Previous research has suggested that ASD most likely develops in the womb and that a mother's diet during pregnancy may have an influence. However the results of these studies have been inconsistent, suggesting that other confounding factors, such as a mother's overall health and lifestyle, could also play a role, said the team.
The team set out to assess whether nutrient supplementation during pregnancy is associated with reduced risk of ASD, with and without intellectual disability using three analytical methods to a sample of 273,107 mother-child pairs living in Stockholm, Sweden.
Women reported their use of folic acid, iron, and multivitamin supplements at their first antenatal visit and cases of child ASD were identified from national registers.
Analysis showed no consistent evidence that either iron or folic acid use were associated with a reduced risk of ASD.
The results of the various analyses seemed to be consistent with each other, the team added - suggesting that the association between multivitamins and ASD might not be fully explained by confounding.
"Together, the three analyses appear to point toward a potential inverse association between multivitamin use with ASD with intellectual disability," the team wrote.
However, they noted several study limitations, such as the potential for confounding and difficulty assessing type, timing and dose of supplements.
DeVilbiss and colleagues added that given the strength of evidence supporting the importance of nutritional supplementation during pregnancy for other conditions, it is impossible to imagine that the current results along would impact policy or practice.
However, they note that the results do “raise questions that warrant investigation" and call for verification in randomised studies.
Source: The BMJ
Published online, Open Access, doi: 10.1136/bmj.j4273
“Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study”
Authors: Elizabeth A DeVilbiss, et al