In looking at data collected over more than a decade in Stockholm, Sweden, the study team found that the decline in risk linked to multivitamin use only seemed to be tied to autism with intellectual disabilities attached. The odds of developing autism without an intellectual disability did not seem to be affected.
"A potential link between supplement use during pregnancy and autism is intriguing because it suggests a possible avenue for risk reduction," said Brian Lee, PhD, associate professor in the Dornsife School of Public Health, a fellow in the A.J. Drexel Autism Institute, and senior author of the study published in BMJ (formerly The British Medical Journal).
The study was funded by the National Institutes of Environmental Health Sciences, part of the National Institutes of Health. Data for it was drawn from children living in Stockholm County, Sweden, for at least four years between 2001 and 2011. Only children ranging in age from four to 15 years-old at the end of 2011 were included. To make results more robust, data from siblings was also taken into account to help offset some of the unseen factors in autism development, like heritability or otherwise healthy behaviors.
Comparatively little is known about how diet during pregnancy might affect the risk of a child developing autism, so this study adds information to build upon, according to its lead author, Elizabeth DeVilbiss, PhD, a recent graduate of the Dornsife School of Public Health.
"There have been more studies in recent years about varied aspects of diet during pregnancy and autism risk involving multivitamins, iron, folic acid, vitamin D and more, but the evidence is still inconclusive," said DeVilbiss, now a post-doctoral fellow at the Eunice Kennedy Shriver National Institute of Child Health & Human Development. "More work needs to be done in this area to clarify these potential relationships."
Hoping to clarify further autism risk linked to diet during pregnancy, DeVilbiss, Lee and their team -- which also included researchers from the University of Bristol and the Karolinska Institute -- also looked for potential changes in autism risk related to taking supplemental folic acid and iron. Both are supplements that have commonly been recommended for pregnant women. But neither appeared to have a significant effect on a child's autism development -- positive or negative.
However, there is room for other factors to have influenced those results.
"We cannot rule out potential contributions by iron and folic acid," DeVilbiss said. "Diet during pregnancy is complicated, and there are important factors we can't assess with our data, such as dietary intake, dose and timing. This is clearly an area for future work."
In that future work, the hope is that more specifics can be nailed down. DeVilbiss and Lee's study found links between multivitamin use and potential protection against autism with intellectual disabilities, but a "link" isn't the same as a "cause" in research. Again, it comes down to other factors and variables.
"If there is a causal relationship, we also need to understand whether there is a critical window for exposure, and what specific nutrients and amounts may be required for protection," DeVilbiss said.