Environment Explains ~40–50% of Autism

A synthesis of systematic reviews and meta‑analyses reports that environmental factors may account for roughly 40–50% of variance in autism spectrum disorder liability, while identifying specific consistent associations (advanced parental age, birth complications involving hypoxia/ischemia, some heavy metals, and vitamin D deficiency) and dismissing links for several popular suspects (vaccines, thimerosal, maternal smoking). The authors stress that studies to date have major design limits and call for prospective, precisely timed exposure measurement. — If environmental exposures plausibly explain a large share of ASD risk, public health policy, prenatal care, and research priorities should shift toward testing and mitigating those exposures rather than amplifying unsupported causes.