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PubMed2026

Genetic evidence for a causal relationship between melatonin metabolism and depression.

To investigate the causal relevance of melatonin metabolism, which provides the biological basis for circulating melatonin levels, to specific depression symptom subtypes, we performed a targeted systematic review of melatonin metabolism pathways in the human brain and liver. Using two-sample Mendelian randomization (MR), we assessed the causal effects of metabolism pathways and/or individual genes on major depressive disorder (MDD) and nine symptom subtypes derived from Patient Health Questionnaire-9 (PHQ-9). Instrumental variables (IVs) were expression quantitative trait loci (eQTL) for eight individual genes, one synthesis route, and three degradation routes. Results were assessed using Bayesian colocalization and phenome-wide association analyses. At the pathway-level, the genetically proxied synthesis-route signal was associated with PHQ-9 Assessment 5 (PHQ9A5, OR: 0.89, 95% CI: 0.85-0.93), but sensitivity analyses suggested this association was primarily driven by TPH1 and may reflect serotonin-related biology. In contrast, higher brain melatonin degradation raised the risk of both PHQ9A1 (OR: 1.03, 95% CI: 1.02-1.04) and PHQ9A7 (OR: 1.03, 95% CI: 1.02-1.03). Within degradation, up-regulation of the kynurenine sub-pathway increased the odds of PHQ9A3 (OR: 1.05, 95% CI: 1.02-1.07), PHQ9A4 (OR = 1.04, 95% CI: 1.02-1.06) and PHQ9A7 (OR: 1.05, 95% CI: 1.02-1.07). Gene-level analyses were largely concordant, except for SULT1A1, whose higher expression was genetically protective for PHQ9A3 but risk-increased for PHQ9A1 and PHQ9A4. Overall, these results demonstrate that melatonin metabolism exerts symptom-specific and pathway-specific causal effects on depression. A stratified view of melatonin's role may help optimize the application of exogenous melatonin supplementation.

Melatonin↗

PubMed2026

Impact of kangaroo care on circadian rhythm, growth, physiological stability in premature infants, and cortisol and melatonin levels in maternal breast milk: A randomized controlled trial.

PURPOSE: This study aimed to examine the effects of regular kangaroo care (KC) on sleep-wake cycles, growth, physiological stability, and maternal breast milk cortisol and melatonin levels in premature infants. DESIGN: This study was a parallel group, single-blind, pre-test-post-test, randomised controlled trial (RCT). METHODS: This randomized controlled study was conducted in a neonatal intensive care unit (NICU) in Türkiye between September 2024 and September 2025 Thirty-six premature infants were randomized to intervention (n = 28) or control (n = 28). Infants in the intervention group received KC for three consecutive days, twice daily (10:00 a.m. and 10:00 p.m.) for 60 min per session. Data were collected using the Infant Information Form, Physiological Parameters Monitoring Chart, and Premature Infant Sleep-Wake Cycles Tracking Chart. Sleep-wake cycles were monitored using a Bispectral Index device. Breast milk cortisol and melatonin levels were measured at baseline and on day three using the competitive ELISA method. The study was registered at ClinicalTrials.gov (NCT06589349). RESULTS: Regular KC had a statistically significant effect on BIS values, heart rate, respiratory rate, oxygen saturation, and body temperature (p < 0.05). No statistically significant effects were observed on infant body weight or on maternal breast milk cortisol and melatonin levels (p > 0.05). CONCLUSION: The findings indicate that regular KC is associated with improved regulation of the sleep-wake cycle and enhanced physiological stability in premature infants. No significant changes were observed in maternal breast milk cortisol or melatonin levels following KC.

Humans↗

PubMed2026

Evaluating the utility of melatonin in spine surgery: a systematic review and meta-analysis of randomized clinical trials.

BACKGROUND: Spine surgery is increasingly performed worldwide, and acute postoperative stressors such as pain and anxiety remain highly prevalent despite historical management with opioids and other pharmacological agents. Recently, interest has emerged in melatonin administration given its endogenous physiological roles, low cost, favorable adverse event profile, and documented benefits throughout surgical literature. PURPOSE: This study aims to consolidate the existing evidence on melatonin's utility specifically in spine surgery, an area not yet comprehensively evaluated, to inform clinical practice and enhance spine surgeon comprehension. STUDY DESIGN/SETTING: Preregistered on PROSPERO, this systematic review queried PubMed/MEDLINE, CINAHL, SPORTDiscus, and Web of Science on November 21st, 2025, for studies reporting outcomes following melatonin administration in patients undergoing spine surgery. METHODS: Study quality was assessed using the Cochrane Risk-of-Bias 2 tool. Extracted variables included demographics, comparator medications, dosages, and other relevant details. Statistical analyses included frequency-weighted means (FWMs), associated standard deviations, narrative syntheses, and limited meta-analyses, where appropriate. RESULTS: A total of 6 moderate-quality randomized trials were included from 749 screened. Melatonin (3-10 mg) was administered to 227 patients (FWM age=43.3±8.6 years; 46.2% male; BMI=26.6±3.2 kg/m2), placebo to 125 patients (age=43.2±10.1 years; 60% male; BMI=28.5±4.3 kg/m2), and active pharmacologic comparators (fentanyl, gabapentin, dexmedetomidine, zolpidem) to 151 patients (age=46.6±8.9 years; 40.5% male; BMI=26.3±3.5 kg/m2). Procedures primarily involved uncomplicated lumbar laminectomies (1-4 levels), with outcomes assessed up to 24 hours postoperatively. Melatonin was associated with significant improvements in early postoperative VAS-pain scores, blood-pressure-related, analgesic-related, and anxiety-related outcomes versus placebo across most reporting studies. Compared with active pharmacologic agents, significant benefits were observed only in select nausea- and anxiety-related instances. Limited meta-analysis (n=2) demonstrated higher 24-hour VAS-pain for melatonin versus gabapentin, though mean difference was near-negligible and harbored extensive statistical constraints. CONCLUSION: Melatonin demonstrates variable utility following spine surgery, with generally consistent anxiolysis and frequent benefit versus placebo but less consistent and comparatively weaker efficacy relative to active pharmacologic comparators. Future outcome-homogenous studies incorporating more granular, expansive comparator arms and more robust quantitative analyses are needed to further elucidate melatonin's role in advancing spine care. LEVEL OF EVIDENCE: Level II.

Humans↗

PubMed2026

Spermidine and melatonin ameliorate heat stress-induced decline in sheep semen quality.

Heat stress impairs reproductive performance in sheep through endocrine disruption and oxidative stress. This study evaluated the protective effects of spermidine (SPD) and melatonin (MT) supplementation on semen quality in Dorper rams during summer. Twenty-four rams were randomly assigned to a control group, an SPD group (5 mg/kg, dietary supplementation), or an MT group (60 mg, subcutaneous implantation) and treated for 60 days. The temperature-humidity index (THI) was monitored throughout the experimental period. Compared with the control group, MT significantly reduced serum cortisol concentration on day 30 (P < 0.05), whereas no significant differences were observed at the other sampling time points. Serum testosterone, spermidine, and melatonin concentrations remained unchanged throughout the study (P > 0.05). SPD supplementation significantly increased ejaculate volume on day 35 and sperm motility on day 42 (P < 0.05), whereas MT did not significantly affect these parameters. Neither treatment reduced the overall sperm abnormality rate. However, both SPD and MT significantly decreased the proportion of acephalic and decaudated sperm on day 56 (P < 0.05). Neither treatment significantly affected pregnancy rate, delivery rate, or the expression of PMFBP1 and SUN5 proteins in semen (P > 0.05). Regarding oxidative stress, MT significantly downregulated CAT protein expression (P < 0.05), whereas SPD significantly reduced MDA content and SOD1 protein expression (P < 0.05); MT showed similar but non-significant trends for these two markers (P > 0.05). Collectively, these findings demonstrate that SPD and MT exert distinct protective effects against heat stress, with SPD improving selected semen quality traits and both treatments reducing sperm head-tail separation, although these benefits did not translate into improved reproductive performance.

Animals↗

PubMed2026

Comparative effectiveness and safety of pharmacological interventions for sleep outcomes in chronic non-cancer pain: a systematic review and network meta-analysis.

Sleep disturbances are highly prevalent among individuals with chronic non-cancer pain and are associated with worse pain severity and poorer prognosis. The comparative trade-offs between the effectiveness and safety of available pharmacotherapies for sleep outcomes in this population remain poorly defined. Ninety-eight RCTs involving 28,920 participants (mean age 53.2 years, 71.2% female) were included. Moderate-certainty evidence demonstrated that melatonin significantly improved sleep quality compared with placebo (standardized mean difference [SMD] = -0.60, 95%CI: -0.98, -0.22). Ten agents (e.g., amitriptyline, oxycodone, gabapentin, pregabalin, duloxetine) also showed statistically significant improvements in subjective sleep quality (SMD = -0.24 to -1.07), but most effects were supported by low-certainty evidence and were accompanied by an increased risk of adverse events (odds ratio [OR] = 1.90 to 37.00). Conversely, melatonin was not associated with an increased risk (OR = 0.88, 95%CI: 0.19, 3.94). Our findings indicate that melatonin shows promise as a safe, adjunctive option for improving sleep quality in this population, but larger, condition-specific trials are warranted to confirm these effects. Other pharmacological agents are limited by lower-certainty and unfavorable safety profiles. These results should be interpreted cautiously given limited direct comparisons, heterogeneous chronic pain populations, the high proportion of trials at high risk of bias, and the predominance of subjective sleep outcomes.

Humans↗

PubMed2026

Boosting kynurenic acid in kombucha via substrate selection: metagenomic and biochemical insights.

Kombucha is gaining global popularity for its health benefits. This study explored the use of chestnut honey, a rich source of kynurenic acid (KYNA), to produce kombucha enriched with this metabolite. Five variants were prepared using different green/black tea blends and carbon sources: white sugar or acacia honey (controls) versus chestnut honey. Samples were analyzed for tryptophan metabolites, physicochemical properties, and microbial diversity. Komagataeibacter and Enterobacter were predominant bacterial genera in SCOBY. Candida and Aspergillus were predominated in the single sample analyzed for fungi. During fermentation, tryptophan decreased, while kynurenine increased. KYNA levels remained largely stable during fermentation and were mainly influenced by the fermentation substrate. No melatonin pathway derivatives were detected. On day 7, chestnut honey yielded kombucha with 381.680-739.915 μmol/L KYNA and elevated myricetin. Overall, chestnut honey-based kombucha represents a system in which substrate composition appears to be the main factor influencing KYNA levels in the final beverage.

Kynurenic Acid↗

PubMed2026

Differences in circadian rhythm changes between myopic and non-myopic college students over 2 years.

This study aimed to characterize and compare the differences in circadian rhythm changes during 2 years between college students with myopia and non-myopia based on a longitudinal cohort study. Wake-up time and bedtime were obtained through a self-administered questionnaire. Chronotype was assessed using the reduced Morningness-Eveningness Questionnaire (rMEQ). Circadian rhythm timing was determined by dim-light melatonin onset (DLMO), measured through hourly saliva collection from 21:00 to 01:00. A total of 450 college students (146 [32.4%] males) with a mean age of 18.65 ± 1.05 years were included, of whom 353 (78.4%) students had myopia. Compared with non-myopic individuals, myopic students slept later, woke up earlier, and exhibited lower rMEQ scores at baseline. Over the 2-year follow-up, both groups showed significantly earlier bedtimes, later wake-up times, and higher rMEQ scores. Only myopic students demonstrated a 45-minute delay in DLMO after the 2-year follow-up. After adjusting for potential confounders, linear mixed-effects models showed that myopic individuals had later bedtimes and earlier wake-up times. These findings indicate significant circadian rhythm changes in individuals with myopia, suggesting the potential of targeted sleep rhythm interventions on preventing myopia.

Myopia↗

PubMed2026

Selective monitoring of trace-level catechin and myricetin in herbal and aqueous matrices using magnetic MIP-DSPME: Optimization via design of experiments.

A novel dispersive solid-phase microextraction approach utilizing a magnetic molecularly imprinted polymer (MMIP) integrated with HPLC-UV detection was developed for the concurrent quantification of catechin and myricetin in herbal extracts and aqueous samples. The sorbent was engineered as a core-shell nanocomposite, consisting of a selective polymer layer deposited onto Fe3O4@SiO2-APTMS magnetic nanoparticles. Dual-template imprinting using catechin and myricetin generated complementary binding cavities within the polymer framework. Experimental variables influencing extraction were systematically screened and subsequently optimized. A Plackett-Burman design was first applied to identify the most influential factors, with pH and sorption time identified as the dominant variables. These parameters were subsequently fine-tuned using a central composite design, and the optimization process was completed in only 30 experimental runs. The sorption characteristics of the imprinted sorbent (MMIP) were compared with those of its non-imprinted counterpart (MNIP). The MMIP demonstrated markedly higher maximum binding capacities (Qmax), reaching 119.3 mg g-1 for myricetin and 112.1 mg g-1 for catechin, whereas the corresponding values for the MNIP were 32.55 and 32.08 mg g-1, respectively. Moreover, the affinity constants (KL = 0.760-0.950 L mg-1) were approximately 2.3-fold higher for the MMIP, confirming its stronger and more selective interactions with the target analytes. The selectivity coefficients for the targeted flavonoids relative to structurally related compounds, including ferulic acid, p-coumaric acid, melatonin, and curcumin, exceeded 3.5 for the MMIP, whereas the corresponding values for the MNIP were close to 1.1, demonstrating the high molecular recognition capability of the imprinted sorbent. Method validation demonstrated limits of detection (LODs) of 0.33-0.59 ng mL-1 and limits of quantification (LOQs) of 1.10-1.96 ng mL-1, and excellent linearity over the concentration range of 5.0-5500 ng mL-1 (R2 > 0.998). The method achieved recoveries of 93.96% to 105.69% with RSDs below 5.5%, while the preconcentration factors ranged from 209 to 229. Furthermore, the sorbent retained more than 95% of its extraction efficiency after four consecutive reuse cycles and more than 80% after six cycles, demonstrating excellent stability and reusability. The proposed method was successfully applied to the analysis of six medicinal plant extracts and water samples, showing negligible matrix interference and superior sensitivity, selectivity, and operational simplicity compared with conventional solid-phase extraction methods.

Flavonoids↗