Maternal vitamin D during pregnancy and offspring autism and autism-associated traits: a prospective cohort study.
Paul Madley-Dowd, Christina Dardani, Robyn E Wootton and 7 others
PMID 36371219WHAT IT FOUND
Maternal vitamin D levels during pregnancy showed no association with offspring autism diagnosis or autism-associated traits in this large cohort.
Neither observational analyses nor genetic methods suggested a causal link, contradicting some previous studies.
Key findings
01There was no strong evidence for an association between maternal vitamin D levels and offspring autism diagnosis or any of the four autism-associated traits.
02Mendelian randomization analyses, which use genetic variants to test for causal effects, found no evidence that maternal vitamin D levels causally influence offspring autism outcomes.
03While some secondary analyses using splines suggested potential nonlinear associations at extreme low levels, these findings were not robust to missing data handling and the primary linear analyses were null.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study had low power to detect effects on diagnosed autism, with only 93 cases (1.2% of the sample). The cohort had few women with deficient vitamin D levels (5%), potentially limiting the ability to detect effects at extreme lows compared to other populations. The sample was disproportionately affluent and White European, which may limit generalizability. Missing data was associated with both exposure and outcome, introducing potential bias despite the use of multiple imputation. The genetic instrument for vitamin D was weak, explaining only 1.05% of variance, which reduces the precision and power of the Mendelian randomization analysis.
Declared interests
The study was funded by the Wellcome Trust and the University of Bristol. The authors declared no competing interests.
The easy way to misread this
Do not conclude that vitamin D supplementation during pregnancy is useless for all health outcomes. This study only addresses the specific question of autism risk and traits. The null finding here contradicts some earlier observational studies, but the authors note that their cohort had fewer deficient mothers than others, so it may not capture risks associated with severe deficiency.