Melatonin Patterns and Levels During the Human Menstrual Cycle and After Menopause

The Impact of Pupil Constriction on the Relationship Between Melanopic EDI and Melatonin Suppression in Young Adult Males

The pupil modulates the amount of light that reaches the retina. Not only luminance but also the spectral distribution defines the pupil size. Previous research has identified steady-state pupil size and melatonin attenuation to be predominantly driven by melanopsin, which is expressed by a unique subgroup of intrinsically photosensitive retinal ganglion cells (ipRGCs) that are sensitive to short-wavelength light (~480 nm). Here, we aimed to selectively target the melanopsin system during the evening, while measuring steady-state pupil size and melatonin concentrations under commonly experienced evening light levels (<90 lx). Therefore, we used a five-primary display prototype to generate light conditions that were matched in terms of L-, M-, and S-cone-opic irradiances, but with high and low melanopic irradiances (~3-fold difference). Seventy-two healthy, male participants completed a 2-week study protocol. The volunteers were assigned to one of the four groups that differed in luminance levels (27-285 cd/m2). Within the four groups, each volunteer was exposed to a low melanopic (LM) and a high melanopic (HM) condition. The two 17-h study protocols comprised 3.5 h of light exposure starting 4 h before habitual bedtime. Median pupil size was significantly smaller during HM than LM in all four light intensity groups. In addition, we observed a significant correlation between melanopic weighted corneal illuminance (melanopic equivalent daylight illuminance [mEDI]) and pupil size, such that higher mEDI values were associated with smaller pupil size. Using pupil size to estimate retinal irradiance showed a qualitatively similar goodness of fit as mEDI for predicting melatonin suppression. Based on our results here, it remains appropriate to use melanopic irradiance measured at eye level when comparing light-dependent effects on evening melatonin concentrations in healthy young people at rather low light levels.

The Menstrual Cycle and Sleep

Aspects of sleep change across the menstrual cycle in some women. Poorer sleep quality in the premenstrual phase and menstruation is common in women with premenstrual symptoms or painful menstrual cramps. Although objective sleep continuity remains unchanged across the regular, asymptomatic menstrual cycle, activity in the sleep electroencephalogram varies, with a prominent increase in sleep spindle activity in the postovulatory luteal phase, when progesterone is present, relative to the follicular phase. Menstrual cycle phase, reproductive stage, and menstrual-related disorders should be considered when assessing women's sleep complaints.

Effects of Melatonin Supplementation on Lipid Metabolism and Body Fat Accumulation in Ovariectomized Rats

Postmenopausal obesity is a rising problem. Melatonin (Mel) is a hormone secreted by the pineal gland that regulates the circadian rhythms and improves obesity. In this experiment, ovariectomized (OVX) rats were used as a menopause model to explore the effects of Mel supplementation on lipid metabolism, body fat accumulation, and obesity. Nine-week-old female rats underwent an OVX surgery and were assigned to the following groups: control group (C), low-dose group (L, 10 mg/kg body weight (BW) Mel), medium-dose group (M, 20 mg/kg BW Mel), and high-dose group (H, 50 mg/kg BW Mel), administered by gavage for 8 weeks. The results showed that the OVX rats supplemented with low, medium, and high doses of Mel for 8 weeks exhibited reduced BW gain, perirenal fat mass, and gonads fat mass, and an increased serum irisin level. Low and high doses of Mel induced brite/beige adipocytes in the white adipose tissues. In addition, the messenger RNA levels of the fatty acid synthesis enzymes were significantly reduced after the high-dose Mel supplementation. Thus, Mel can reduce the hepatic fatty acid synthesis and promote the browning of white adipose tissues through irisin; thereby, improving obesity and body fat accumulation in OVX rats.

Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness

Evening light-emitting visual displays may disrupt sleep, suppress melatonin and increase alertness. Here, we control melanopic irradiance independent of display luminance and colour, in 72 healthy males 4 h before habitual bedtime and expose each of them to one of four luminance levels (i.e., dim light, smartphone, tablet or computer screen illuminance) at a low and a high melanopic irradiance setting. Low melanopic light shortens the time to fall asleep, attenuates evening melatonin suppression, reduces morning melatonin, advances evening melatonin onset and decreases alertness compared to high melanopic light. In addition, we observe dose-dependent increases in sleep latency, reductions in melatonin concentration and delays in melatonin onset as a function of melanopic irradiance-not so for subjective alertness. We identify melanopic irradiance as an appropriate parameter to mitigate the unwanted effects of screen use at night. Our results may help the many people who sit in front of screens in the evening or at night to fall asleep faster, feel sleepier, and have a more stable melatonin phase by spectrally tuning the visual display light without compromising the visual appearance.

Homo sapiens May Incorporate Daily Acute Cycles of “Conditioning–Deconditioning” to Maintain Musculoskeletal Integrity: Need to Integrate with Biological Clocks and Circadian Rhythm Mediators

Human evolution required adaptation to the boundary conditions of Earth, including 1 g gravity. The bipedal mobility of Homo sapiens in that gravitational field causes ground reaction force (GRF) loading of their lower extremities, influencing the integrity of the tissues of those extremities. However, humans usually experience such loading during the day and then a period of relative unloading at night. Many studies have indicated that loading of tissues and cells of the musculoskeletal (MSK) system can inhibit their responses to biological mediators such as cytokines and growth factors. Such findings raise the possibility that humans use such cycles of acute conditioning and deconditioning of the cells and tissues of the MSK system to elaborate critical mediators and responsiveness in parallel with these cycles, particularly involving GRF loading. However, humans also experience circadian rhythms with the levels of a number of mediators influenced by day/night cycles, as well as various levels of biological clocks. Thus, if responsiveness to MSK-generated mediators also occurs during the unloaded part of the daily cycle, that response must be integrated with circadian variations as well. Furthermore, it is also possible that responsiveness to circadian rhythm mediators may be regulated by MSK tissue loading. This review will examine evidence for the above scenario and postulate how interactions could be both regulated and studied, and how extension of the acute cycles biased towards deconditioning could lead to loss of tissue integrity.

The Reproductive Functions of the Human Brain Regions: A Systematic Review

Reproduction remains a vital characteristic of living things necessary for survival and continuity. Specific brain regions and structures are responsible for regulating the different aspects of human reproduction. This study systematically reviewed the brain regions that play structural, hormonal and physiological roles in controlling the various aspects of human reproduction from puberty, sexual function, gametogenesis, childbirth and fertility to infertility to inform advancement in research and therapeutic interventions in human reproductive disorders. A systematic literature search of online databases (MEDLINE, Europe PMC and Google Scholar) was made using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for observational and cross-sectional studies providing evidence for the role(s) of the brain region in human reproduction from the year 2011-2021. Out of 141 articles found, 15 studies met the inclusion criteria, including six cross-sectional and nine randomised controlled trials. The study acknowledged the roles of the pituitary gland, hypothalamus and pineal gland, widely known for regulating the human reproductive system in a gender-based approach while highlighting essential gaps and opportunities for future research. This review provides a 10-year update and overview of the role of different brain regions in human reproduction and will stimulate future research in human reproduction.

Vasomotor menopausal disorders as a possible result of dysfunction of the microbiota-intestine-brain axis

The study involved clinical and laboratory examination of 54 women with vasomotor menopausal disorders divided into 3 subgroups depending on the duration of symptoms (not more than 12 months, about 3 years, from 5 to 7 years). The control group included 21 patients without vasomotor disorders during the menopausal period. Data from the general and obstetric-gynecological anamnesis and the results of objective and general clinical examinations were analyzed. To assess the state of intestinal microbiocenosis in patients, a bacteriological study of feces was used according to modern methods. In women with menopausal vasomotor disorders, chronic arterial hypertension, overweight, diabetes mellitus, chronic enterocolitis, and chronic pyelonephritis prevailed among somatic diseases. The study also revealed that these patients had a pronounced imbalance of the intensive microbiota, which was characterized by a significant decrease in the main representatives of the obligate microflora (Bifidobacterium, Lactobacillus) and an increase in the number of opportunistic strains (Klebsiella and Clostridiodes difficile). Considering modern concepts, a change in the microbial composition of the intestine may be one of the possible trigger factors for the occurrence of vasomotor menopausal disorders. Further research will clarify the influence of the microbiome on the formation of the pathological menopausal symptom complex and improve the preventive and therapeutic measures in this category of women.

Sleep pattern and bone mineral density: a cross-sectional study of National Health and Nutrition Examination Survey (NHANES) 2017-2018

This research is a cross-sectional study based on the participants aged 50 years and older from National Health and Nutrition Examination Survey (NHANES) database. Poor sleep patterns were associated with lower bone mineral density (BMD) and a higher risk of osteoporosis, especially among older individuals or females.

INTRODUCTION

Accumulated evidence demonstrates that sleep duration, which is one aspect of sleep pattern, is associated with the risk of osteoporosis. However, the related studies on the association between sleep patterns and the risk of osteoporosis were limited. Therefore, this research aims to investigate the association of sleep patterns with BMD and the risk of osteoporosis among individuals aged 50 years and older.

METHODS

Participants aged ≥ 50 years from the NHANES database were included in the present study. The diagnosis of osteoporosis was based on the results of BMD testing. Moreover, all the participants were divided into different sleep pattern groups according to nocturnal sleep duration and bedtime. In addition, this study used multivariate linear regression models to evaluate the association between sleep patterns and BMD and exploited multiple logistic regression models to investigate the odds ratios (ORs) for osteoporosis.

RESULTS

Finally, 1,865 individuals (non-osteoporosis: N = 1,713; osteoporosis: N = 152) aged over 50 years old with complete data were analyzed. The results of multivariate linear regression models showed that individuals with normal sleep duration/later bedtime or long sleep duration/later bedtime had lower femoral BMD than those with normal sleep duration/usual bedtime. Moreover, subjects with long sleep duration/later bedtime had a higher risk of osteoporosis compared with those with normal sleep duration/usual bedtime. In addition, subgroup analyses revealed the association of sleep patterns with BMD and the risk of osteoporosis appeared to be more pronounced among individuals aged ≥ 65 years or females.

CONCLUSION

This study demonstrated that sleep patterns are associated with BMD and the risk of osteoporosis. Poor sleep patterns contribute to decreased bone mass and the increased risk of osteoporosis. Therefore, a healthy sleep pattern is favorable for the prevention of osteoporosis.

Melatonin effects on bone: Implications for use as a therapy for managing bone loss

Melatonin is the primary circadian output signal from the brain and is mainly synthesized in pinealocytes. The rhythm and secretion of melatonin are under the control of an endogenous oscillator located in the SCN or the master biological clock. Disruptions in circadian rhythms by shift work, aging, or light at night are associated with bone loss and increased fracture risk. Restoration of nocturnal melatonin peaks to normal levels or therapeutic levels through timed melatonin supplementation has been demonstrated to provide bone-protective actions in various models. Melatonin is a unique molecule with diverse molecular actions targeting melatonin receptors located on the plasma membrane or mitochondria or acting independently of receptors through its actions as an antioxidant or free radical scavenger to stimulate osteoblastogenesis, inhibit osteoclastogenesis, and improve bone density. Its additional actions on entraining circadian rhythms and improving quality of life in an aging population coupled with its safety profile make it an ideal therapeutic candidate for protecting against bone loss in susceptible populations. The intent of this review is to provide a focused discussion on bone loss and disorders of the bone as it relates to melatonin and conditions that modify melatonin levels with the hope that future therapies include those that include melatonin and correct those factors that modify melatonin levels like circadian disruption.

Chronological Age Interacts with the Circadian Melatonin Receptor 1B Gene Variation, Determining Fasting Glucose Concentrations in Mediterranean Populations. Additional Analyses on Type-2 Diabetes Risk

Gene-age interactions have not been systematically investigated on metabolic phenotypes and this modulation will be key for a better understanding of the temporal regulation in nutrigenomics. Taking into account that aging is typically associated with both impairment of the circadian system and a decrease in melatonin secretion, we focused on the melatonin receptor 1B (MTNR1B)-rs10830963 C>G variant that has been associated with fasting glucose concentrations, gestational diabetes, and type-2 diabetes. Therefore, our main aim was to investigate whether the association between the MTNR1B-rs10830963 polymorphism and fasting glucose is age dependent. Our secondary aims were to analyze the polymorphism association with type-2 diabetes and explore the gene-pregnancies interactions on the later type-2 diabetes risk. Three Mediterranean cohorts (n = 2823) were analyzed. First, a cross-sectional study in the discovery cohort consisting of 1378 participants (aged 18 to 80 years; mean age 41 years) from the general population was carried out. To validate and extend the results, two replication cohorts consisting of elderly individuals were studied. In the discovery cohort, we observed a strong gene-age interaction (p = 0.001), determining fasting glucose in such a way that the increasing effect of the risk G-allele was much greater in young (p = 5.9 × 10^-10) than in elderly participants (p = 0.805). Consistently, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose concentrations in the two replication cohorts (mean age over 65 years) did not reach statistical significance (p > 0.05 for both). However, in the elderly cohorts, significant associations between the polymorphism and type-2 diabetes at baseline were found. Moreover, in one of the cohorts, we obtained a statistically significant interaction between the MTNR1B polymorphism and the number of pregnancies, retrospectively assessed, on the type-2 diabetes risk. In conclusion, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose is age-dependent, having a greater effect in younger people. However, in elderly subjects, associations of the polymorphism with type-2 diabetes were observed and our exploratory analysis suggested a modulatory effect of the number of past pregnancies on the future type-2 diabetes genetic risk.