Measuring morning melatonin levels with plasma melatonin ELISA kits is a poor choice on two levels

Associations between systemic melatonin and human myopia: A systematic review

PURPOSE

Experimental models have implicated the role of melatonin circadian rhythm disruption in refractive error development. Recent studies have examined melatonin concentration and its diurnal patterns on refractive error with equivocal results. This systematic review aimed to summarise the literature on melatonin circadian rhythms in myopia.

RECENT FINDINGS

PubMed, EMBASE, Web of Science, Scopus, ProQuest Central, LILACS, Cochrane and Medline databases were searched for papers between January 2010 and December 2022 using defined search terms. Seven studies measured melatonin and circadian rhythms in three biological fluids (blood serum, saliva and urine) in both myopes and non-myopes. Morning melatonin concentrations derived from blood serum varied significantly between studies in individuals aged 10-30 years, with a maximum of 89.45 pg/mL and a minimum of 5.43 pg/mL using liquid chromatography and mass spectrometry. The diurnal variation of salivary melatonin was not significantly different between myopes and emmetropes when measured every 4 h for 24 h and quantified with enzyme-linked immunosorbent assay. Significantly elevated salivary melatonin concentrations were reported in myopes compared with emmetropes, aged 18-30 years when measured hourly from evening until their habitual bedtime using liquid chromatography. However, the relationship between dim light melatonin onset and refractive group was inconsistent between studies. The 6-sulphatoxymelatonin concentration derived from overnight urine volume, measured using a double antibody radioimmunoassay, was found to be significantly lower in myopes (29.17 pg/mL) than emmetropes (42.51 pg/mL).

SUMMARY

The role of melatonin concentration and rhythm in myopia has not been studied extensively. This systematic review confirms conflicting findings across studies, with potential relationships existing. Future studies with uniform methodological approaches are required to ascertain the causal relationship between melatonin dysregulation and myopia in humans.

A Cross-Sectional Study of Myopia and Morning Melatonin Status in Northern Irish Adolescent Children

Purpose

Previous studies have demonstrated an association between melatonin status and both refractive error and axial length in young adult myopes. This study aimed to determine if this relationship extends to a younger adolescent cohort.

Methods

Healthy children aged 12-15 years provided morning saliva samples before attending Ulster University (55°N) for cycloplegic autorefraction and axial length measures. Participants completed questionnaires describing recent sleep habits and physical activity. Salivary melatonin was quantified using high-performance liquid chromatography-tandem mass spectrometry. Data collection for all participants occurred over a 1-week period (April 2021).

Results

Seventy participants aged 14.3 (95% CI: 14.2-14.5) years were categorised by spherical equivalent refraction [SER] (range: -5.38DS to +1.88DS) into two groups; myopic SER ≤ -0.50DS (n = 22) or nonmyopic -0.50DS < SER ≤ +2.00DS (n = 48). Median morning salivary melatonin levels were 4.52 pg/ml (95% CI: 2.60-6.02) and 4.89 pg/ml (95% CI: 3.18-5.66) for myopic and nonmyopic subjects, respectively, and did not differ significantly between refractive groups (P = 0.91). Melatonin levels were not significantly correlated with SER, axial length, sleep, or activity scores (Spearman's rank, all P > 0.39). Higher levels of physical activity were associated with higher sleep quality (Spearman's rank, ρ = -0.28, P = 0.02).

Conclusion

The present study found no significant relationship between morning salivary melatonin levels and refractive error or axial length in young adolescents. This contrasts with outcomes from a previous study of adults with comparable methodology, season of data collection, and geographical location. Prospective studies are needed to understand the discrepancies between adult and childhood findings and evaluate whether melatonin levels in childhood are indicative of an increased risk for future onset of myopia and/or faster axial growth trajectories and myopia progression in established myopes. Future work should opt for a comprehensive dim-light melatonin onset protocol to determine circadian phase.

Overnight Melatonin Concentration and Sleep Quality Are Associated with the Clinical Features of Polycystic Ovary Syndrome

Circulating melatonin is elevated in women with polycystic ovary syndrome (PCOS); whether circadian disruptions coincide with sleep disturbances in women with PCOS or their symptom severity is unclear. The objective of this observational pilot study was to determine whether altered patterns of melatonin excretion are associated with reduced sleep quality in women with versus without PCOS. Participants underwent a clinical assessment, transvaginal ultrasound, and reproductive hormone testing. Morning and evening urine samples were assayed for urinary 6-sulfatoxymelatonin (MEL) as a proxy for melatonin production. The night (morning MEL)-to-day (evening MEL) ratio, or N:D ratio, was determined to approximate the rhythm of MEL production. Sleep quality and duration were assessed using the Pittsburgh Sleep Quality Index (PSQI) and wrist actigraphy. No differences were detected in overnight MEL, daytime MEL, or the N:D ratio in participants with PCOS versus controls. The PCOS group experienced reduced weekend sleep efficiency vs. controls (81% vs. 88% p < 0.05). The number of follicles per ovary (FNPO) was positively associated with overnight MEL (r = 0.359, p < 0.05). Weekend sleep time and overnight MEL concentrations were dependent on PCOS status. Therefore, diagnostic features of PCOS were associated with MEL production and sleep disturbances, suggesting that women with a more severe clinical presentation of PCOS may be more likely to experience altered MEL production or sleep disturbances.

Development and Validation of an Ultrasensitive LC-MS/MS Method for the Quantification of Melatonin in Human Saliva

A growing body of literature describes the potential effects of circadian disruption on human health. Indeed, psychiatric diseases, metabolic syndrome, and cancers may be linked to disturbance of the circadian rhythm. Currently, the best practice to assess circadian rhythm is the measurement of melatonin levels. Our goal was thus to develop and validate a highly sensitive LC-MS/MS method to follow salivary melatonin levels throughout the day and night. Our method reached a lower limit of the measuring interval (LLMI) of 0.8 pg/mL. To our knowledge, it is the most sensitive method allowing quantitation of melatonin in saliva. Saliva, obtained from passive drooling or salivette, was extracted by an efficient and quick liquid-liquid extraction with no further cleanup needed. The method was validated according to the European Medicines Agency (EMA) guidelines and provided excellent results regarding accuracy, precision, linearity, selectivity, and specificity. Comparison between radioimmunoassay and our method was performed and showed differences at low levels, most likely due to cross-reactivity with other indols. To assess daytime melatonin levels in humans, salivary melatonin levels of ten volunteers were monitored throughout the day and showed lower daytime levels than reported in previous studies.