From "Passive Supplementation" to "Active Repair": Melatonin Reshapes the Treatment Paradigm for Late-Onset Hypogonadism by Targeting Leydig Cell Senescence

Chinese TCM researchers propose melatonin could restore endogenous testosterone by repairing aging Leydig cells — supported by animal data and zero LOH clinical trials

Journal: Aging Cell | Published: 2026-05 | Type: Narrative Review | PMID: 42083130 Authors: Wu Hui et al., Department of Andrology, The First Hospital of Hunan University of Chinese Medicine, Changsha, China Funding/COI: Hunan Provincial Natural Science Foundation; National Natural Science Foundation of China; Traditional Chinese Medicine Research Program of Changsha; Natural Science Foundation of Changsha. No conflicts declared.

Summary

This narrative review argues that melatonin could treat late-onset hypogonadism (LOH) by targeting the cellular aging processes in Leydig cells — the testicular cells that synthesize testosterone — rather than supplementing testosterone from outside. The proposed mechanism: melatonin's antioxidant and mitochondria-protective properties slow Leydig cell senescence and restore endogenous testosterone production across multiple pathways simultaneously. The clinical evidence for this claim is essentially absent; the one human trial the authors cite used Parkinson's patients, not LOH patients, and showed "limited superiority over placebo" with no improvement in clinical symptoms.

Claims

• Leydig cell senescence — driven by oxidative stress and mitochondrial dysfunction — is the primary mechanism behind age-related testosterone decline in LOH
• Melatonin theoretically targets multiple senescence pathways simultaneously: oxidative stress, mitochondrial dysfunction, epigenetic remodeling, senescence-associated secretory phenotype (SASP) formation, stem Leydig cell niche degradation, and circadian rhythm disruption
• A single melatonin administration in large animal models improved testicular blood flow and increased testosterone levels
• High-dose melatonin (25 mg twice daily) upregulated BMAL1 gene expression in Parkinson's disease patients but showed "limited superiority over the placebo" and failed to improve clinical symptoms
• Melatonin's effects on testosterone are species-dependent and context-dependent — in rooster models, it consistently inhibits testosterone synthesis via suppression of the AKT/cAMP/PKA pathway

Study Quality

This is a narrative review with no reported systematic search strategy, meaning the authors selected which papers to include without a defined, reproducible methodology. That creates unconstrained risk of cherry-picking supportive evidence. All six authors are from the same andrology department at a Traditional Chinese Medicine hospital, with no external co-investigators, and two of the four funding sources are explicitly TCM-focused programs. The combination of institutional monoculture and TCM-aligned funding raises reasonable concern about motivated reasoning toward a natural supplement conclusion.

The underlying biology is legitimate: Leydig cell senescence, mitochondrial dysfunction, SASP, and circadian disruption in aging testes are real and active research areas. But the leap from "melatonin does interesting things in cell and rooster models" to "melatonin reshapes the treatment paradigm for LOH" is not supported by the evidence the authors themselves present. Their own limitations section openly states that melatonin effects are "highly dependent on physiological and pathological context" and cautions against extrapolating from animal models to humans "without rigorous validation" — a statement that undermines the paper's bullish thesis.

Red Flags

• Narrative review with no systematic search protocol — selection bias is uncontrolled and unquantifiable
• Zero completed clinical trials in LOH patients cited anywhere in the paper
• The sole cited human trial enrolled Parkinson's patients, not LOH patients, and the result was "limited superiority over placebo" with no clinical symptom improvement
• Authors explicitly acknowledge melatonin can inhibit testosterone synthesis in some species — making simple translational extrapolation invalid
• Title uses paradigm-shift framing ("Reshapes the Treatment Paradigm") unsupported by the evidence base within the paper
• All six authors from the same single institution; two funding bodies are Traditional Chinese Medicine programs
• Heavy reliance on rooster and rodent models; authors themselves flag species-divergence as a core limitation

Strengths

• Unusually candid limitations section — the species-dependence caveat and the warning against direct extrapolation from animal models are more honest than the abstract's framing suggests
• The mechanistic framework (Leydig cell senescence as the root cause of LOH) is well-grounded in the existing aging biology literature
• Correctly identifies the key translational bottlenecks: optimal dosing, delivery route, long-term safety, and patient selection biomarkers
• Raises a genuinely useful research hypothesis: melatonin's value may be specific to particular etiologies (toxicant-induced, metabolic stress-induced testicular dysfunction) rather than universal across all LOH presentations

Verdict

A speculative narrative review dressed in paradigm-shift language. The hypothesis — melatonin as a cellular repair agent for age-related testosterone decline — is biologically coherent and worth investigating, but the paper presents no clinical evidence to justify its confident framing. The preclinical data is contradictory across species (inhibitory in roosters, stimulatory in some mammalian models), the only human data cited comes from an irrelevant patient population and barely beat placebo, and the single-institution TCM authorship with TCM funding warrants skepticism about the review's completeness. Useful as a mechanistic orientation to Leydig cell senescence biology; useless as clinical guidance.