Current research suggests that autism spectrum disorders (ASD) occur as a result of events that take place during pregnancy. While genetic factors play an important role, non-heritable risk factors contribute to a substantial proportion of ASD cases. Maternal nutrition has been a focus of interest as a factor which may influence risk for ASD. However, results from population-based studies have yielded conflicting results.
In two studies — one an American case-control study, CHARGE (CHildhood Autism Risks from Genetics and Environment) and, the other, a Norwegian cohort study (Norwegian Mother and Child Cohort Study (MoBa)) — maternal folic acid intake during the periconceptual period and early pregnancy was associated with a reduction in risk for of ASD. In the CHARGE study, maternal iron intake and multivitamin use were also associated with a reduced risk of ASD.
On the other hand, a study from the Danish National Birth Cohort (DNBC) found no association between supplementation with folic acid or multivitamins and risk of ASD.
The association between maternal nutrition and risk for ASD may be confounded by certain maternal characteristics. Specifically, do mothers who take folic acid supplements or multivitamins before and during pregnancy differ in some way from women who do not? Potential differences may include socioeconomic status, healthy behaviours, or pregnancy characteristics. In a recent study from Sweden, researchers try to control for these confounding factors using various techniques in order to better clarify the association between maternal nutrition status and risk for ASD.
A total of 273,107 mother-child pairs were identified through population registers. The analysis was restricted to children who were between the ages of 4 and 15. Diagnosis of ASD with and without intellectual disability in the children was determined by examination of the register data.
ASD with intellectual disability was identified in 0.26% of the children (158 cases in 61,934) born to mothers in the multivitamin use group and 0.48% (430 cases in 90,480) in the no nutritional supplement use group. Maternal multivitamin use — with or without additional iron or folic acid — was associated with a lower odds of having a child with ASD with intellectual disability compared to mothers who did not use multivitamins, iron, and folic acid (odds ratio 0.69, 95% confidence interval 0.57 to 0.84). Similar estimates were found using propensity score matched and sibling controls.
This and previous studies suggest that maternal multivitamin supplementation during pregnancy may be associated with a decreased risk for ASD with intellectual disability in offspring. While there may be confounding factors which contribute to this association, the risks associated with multivitamin use, specifically folic acid, are low, and the potential benefits of multivitamin use are high. For example, folic acid supplementation early in pregnancy reduces risk of neural tube defects.
Because half of all pregnancies are unplanned, the CDC, the U.S. Public Health Service and the American College of Obstetricians and Gynecologists (ACOG), urge every woman who could become pregnant to take at least 400 micrograms (400 mcg) or 0.4 milligrams of folic acid every day. Most multivitamins contain 400 micrograms or 0.4 milligrams of folic acid. Most prenatal vitamins have approximately 800 micrograms or 0.8 milligrams of folic acid. Some women are more likely to be folate deficient and may need higher doses or alternate forms of folate supplementation.
Ruta Nonacs, MD PhD
DeVilbiss EA, Magnusson C, Gardner RM, Rai D, Newschaffer CJ, Lyall K, Dalman C, Lee BK. Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study. BMJ. 2017 Oct 4;359:j4273. Free Text