Association of Thyroid Hormone and Insulin-Like Growth Factor-1 Levels With Autism Spectrum Disorders: A Systematic Review and Meta-Analysis.

This study looked at hormone levels in people with autism compared to those without autism. While most hormone levels were similar between groups, people with autism had lower levels of a hormone called TSH. More importantly, those with severe autism symptoms had lower levels of several important hormones including thyroid hormones and growth factor. This suggests that hormone problems might be more common in people with more severe autism symptoms.

This systematic review and meta-analysis examined thyroid hormone and insulin-like growth factor-1 (IGF-1) levels in autism spectrum disorder (ASD). Analyzing 16 studies with 2,399 participants (1,285 with ASD, 1,114 controls), researchers found no significant differences in most hormone levels between groups. However, thyroid stimulating hormone (TSH) levels were significantly lower in individuals with ASD. Importantly, subgroup analysis revealed that those with severe ASD symptoms had significantly reduced levels of free triiodothyronine, free thyroxine, and IGF-1.

These findings suggest potential dysfunction of the hypothalamic-pituitary-thyroid axis in severe ASD cases, indicating that hormone dysregulation may be linked to autism severity rather than presence of autism itself.

Results suggest routine thyroid screening may be particularly relevant for individuals with severe ASD symptoms. The findings indicate potential hypothalamic-pituitary-thyroid axis dysfunction in severe cases, warranting further research into hormone-based interventions and the relationship between endocrine function and autism severity.

The study was limited to observational research designs. Heterogeneity was present in some analyses. The relationship between hormone levels and autism severity requires further investigation to establish causality and clinical significance.

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, I = 2%), free thyroxine (n = 153, Hedges' g = -0.72, 95% CI: -1.31 to -0.14, p = 0.02, I = 66%), and IGF-1 (n = 397; Hedges' g = -0.92; 95% CI: -1.30 to -0.55, p < 0.00001, I = 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.