Association of Thyroid Hormone and Insulin-Like Growth Factor-1 Levels With Autism Spectrum Disorders: A Systematic Review and Meta-Analysis.
Thyroid and IGF-1 levels do not flag autism in general, but severe cases may show low free hormones that deserve a second look.
01Research in Context
What this study did
The team pooled every paper that measured thyroid or IGF-1 hormones in kids and adults with autism. They ran a meta-analysis to see if the levels split clearly between ASD and neurotypical groups.
What they found
Across all studies most hormones looked the same in both groups. Only TSH ran a bit lower in ASD. When the authors looked only at severe autism, free thyroid hormone and IGF-1 levels dropped.
How this fits with other research
Rosenthal et al. (1980) first checked thyroid in autism and also saw no clear split. Their small study is now joined by this larger meta, so the old null finding still holds for most cases.
John et al. (2021) used the same meta trick on oxytocin and found a steady drop in autistic kids. The thyroid story is less tidy: only the severe subgroup shows a dip, so the biomarker is weaker.
Panpan et al. (2025) tested trace metals in Chinese children and saw a mixed pattern too. Both papers agree that single blood values rarely give a yes-or-no autism flag.
Why it matters
You can stop chasing routine thyroid or IGF-1 labs for a basic autism work-up. If a learner has severe ASD and slow growth, a quick thyroid check may still help, but mild shifts are probably noise. Save your clinical time for skill-based assessment and intervention.
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02At a glance
03Original abstract
The action of the thyroid hormones and insulin-like growth factor 1 (IGF-1) is interdependent. The levels of thyroid hormone and IGF-1 were reported to be altered in individuals with autism spectrum disorder (ASD), but the results were controversial. This study aims to compare levels of thyroxine, triiodothyronine, thyroid stimulating hormone, and IGF-1 between the ASD group and neurotypical controls. PubMed, Web of Science, Cochrane, and Embase databases were searched for eligible observational studies. We calculated pooled standardized mean difference (SMD) with 95% confidence intervals (CIs) of our data using a random or fixed effect model. The search strategy provided a total of 1710 articles, of which 16 articles were quantitatively analyzed. The total number of included participants was 2399 (1285 cases and 1114 controls). The meta-analysis revealed no significantly changed blood levels of thyroxine, free triiodothyronine, free thyroxine, and IGF-1 of subjects with ASD compared to non-autistic controls. The blood TSH levels were significantly lower in ASD subjects than in controls (n = 859, Hedges' g = -1.18, 95% CI: -2.17 to -0.20, p = 0.02). Subgroup-analysis results showed that blood free triiodothyronine (n = 153, Hedges' g = -0.74, 95% CI: -1.08 to -0.40, p < 0.0001, I2 = 2%), free thyroxine (n = 153, Hedges' g = -0.72, 95% CI: -1.31 to -0.14, p = 0.02, I2 = 66%), and IGF-1 (n = 397; Hedges' g = -0.92; 95% CI: -1.30 to -0.55, p < 0.00001, I2 = 63%) levels were significantly reduced in subjects with severe ASD symptoms. Individuals with severe ASD may experience a dysfunction of the hypothalamic-pituitary-thyroid axis, and further studies are warranted to determine the correlation between thyroid hormone and IGF-1 levels and disease severity. Trial Registration: ClinicalTrials.gov identifiers: NCT01970345.
Autism research : official journal of the International Society for Autism Research, 2025 · doi:10.1002/aur.70052