Letter to the Editor: Insight into the nonlinear association between thyroid-stimulating hormone and suicide risk in first-episode major depressive disorder

Abstract

The relationship between the hypothalamic-pituitary-thyroid (HPT) axis and suicidal behavior in major depressive disorder (MDD) has been a subject of clinical debate for some time. The study by Deng et al published in the recent issue of the World Journal of Psychiatry, present a comprehensive analysis of 1718 Chinese patients with first-episode drug-naïve MDD, identifying a substantial nonlinear relationship between serum thyroid-stimulating hormone (TSH) levels and suicide attempts (SAs). The study identifies a critical inflection point at 5.43 μIU/mL, beyond which each unit increase in TSH correlates with a 21% increase in SA risk. While these findings offer a promising biomarker, they also invite a deeper discussion regarding sexual dimorphism and the metabolic-endocrine nexus. Specifically, the higher prevalence of thyroid dysfunction in women necessitates a more granular, sex-stratified approach to data analysis. Furthermore, the interplay between TSH, lipid metabolism, and glucose regulation-all of which have been independently linked to suicidality-deserves investigation as a unified biosignature. This letter explores the neurobiological mechanisms linking the HPT axis to self-harm, the necessity of sex-sensitive risk thresholds, and the importance of metabolic screening in suicide prevention.

Keywords: Major depressive disorder; Thyroid-stimulating hormone; Suicide attempts; Sex differences; Metabolic markers; First-episode drug-naïve

Core Tip: Deng et al identify a TSH threshold of 5.43 μIU/mL as a significant predictor of suicide attempts in first-episode drug-naïve-major depressive disorder (MDD) patients. However, to translate these findings into clinical practice, researchers must account for the biological reality that hypothyroidism and MDD phenotypes differ significantly by sex. Additionally, the relationship between thyroid-stimulating hormone and suicide should be interpreted within the broader context of metabolic health, as thyroid function and lipid/glucose metabolism are physiologically intertwined and collectively influence neurobiological vulnerability to self-harm.