Alterations with aging of the endocrine and neuroendocrine circadian system in humans

Modified Cortisol Circadian Rhythm: The Hidden Toll of Night-Shift Work

The circadian rhythm of cortisol, a key hormone essential for maintaining metabolic balance and stress homeostasis, is profoundly disrupted by night-shift work. This narrative review examines the physiological mechanisms underlying cortisol regulation, the effects of shift work on its circadian rhythm, the associated health risks, and potential mitigation strategies. Night-shift work alters the natural secretion pattern of cortisol, leading to dysregulation of the hypothalamic-pituitary-adrenal axis, which in turn can contribute to metabolic disorders, cardiovascular diseases, and impaired cognitive function. Understanding the physiological pathways mediating these changes is crucial for developing targeted interventions to mitigate the adverse effects of circadian misalignment. Potential strategies, such as controlled light exposure, strategic napping, and personalized scheduling, may help to stabilize cortisol rhythms and improve health outcomes. This review aims to provide insights that can guide future research and inform occupational health policies for night-shift workers by addressing these challenges.

Autonomic nervous system and endocrine system response to upper or lower cervical spine mobilization in males with persistent post-concussion symptoms: a proof-of-concept trial

INTRODUCTION

The peripheral stress response, consisting of the autonomic nervous system (ANS) and hypothalamic pituitary adrenal-axis (HPA-axis), functions to maintain homeostasis in response to stressors. Cervical spine manual therapy has been shown to differentially modulate the stress response in healthy populations. No study has investigated whether cervical spine mobilizations can differentially modulate the stress response in individuals with persistent post-concussion symptoms (PPCS), a population characterized by a dysfunctional stress response.

METHODS

A randomized, controlled, parallel design trial was performed to investigate whether upper or lower cervical spine mobilization can differentially modulate components of the stress response in individuals with PPCS. The outcomes were salivary cortisol (sCOR) concentration (primary) and the HRV metric, rMSSD, measured with a smartphone application (secondary). Nineteen males diagnosed with PPCS, aged 19-35, were included. Participants were randomly assigned into either intervention group, upper (n = 10) or lower (n = 9) cervical spine mobilization. Each outcome was collected at different time points, pre- and post-intervention. Statistical analyses were performed using the Friedman's Two-Way ANOVA, Mann-Whitney U test, and Wilcoxon Signed Rank Test.

RESULTS

There was a statistically significant within-group reduction in sCOR concentration 30 minutes following lower cervical spine mobilizations and statistically significant within-group increase in rMSSD 30 minutes following upper cervical spine mobilizations.

CONCLUSION

The results of this trial provide preliminary evidence for cervical spine mobilizations to differentially modulate components of the stress response at specific time points. Understanding the mechanisms of the effect of cervical spine mobilizations on the stress response provides a novel rationale for selecting cervical spine mobilizations to rehabilitate individuals with PPCS.

Circadian Rhythm of Distal Skin Temperature in Healthy Older and Young Women and Its Relationship with Sleep-Wake Rhythm and Environmental Factors under Natural Living Conditions

Little is known about the healthy aging of the circadian timing system under natural living conditions. This study explores changes in the circadian rhythm of distal skin temperature (DST) with aging and relates these changes to sleep-wake timing and environmental influences. DST, sleep-wake timing, 24-h light exposure, and physical activity were measured and averaged over seven consecutive days using temperature sensors, actigraphy with a light meter, and sleep diaries in 35 healthy older women (60-79 years) and 30 young women (20-34 years). Circadian rhythm characteristics, describing strength (amplitude) and timing (acrophase) of the DST rhythm, were calculated using cosinor analysis. The older adults displayed an 18-19% smaller amplitude and a 66-73 min earlier acrophase (peak time) for DST rhythm than the young adults, indicating a weaker and phase-advanced DST rhythm. The phase advance for DST was not due to an earlier evening increase, but to a shorter nocturnal plateau period. Daytime light exposure inversely affected strength (amplitude) but not phasing of the DST rhythm in older adults. The DST rhythm was 3.5 times more advanced than the sleep-wake rhythm, showing an altered phase relationship (phase angle) between both rhythms with aging. The phase angle was more heterogeneous among older adults, showing differential aging. The phase advance for DST rhythm and the altered and heterogeneous phase relationship between DST and sleep-wake rhythms were not related to ambient light exposure and the physical activity of older adults. This suggests that healthy aging of the circadian system might be due to endogenous mechanisms such as an internal rearrangement rather than external influences.

Preservation of Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) in Late Adult Mice: Implications as a Potential Biomarker for Early Onset Ocular Degenerative Diseases

Purpose

Intrinsically photosensitive retinal ganglion cells (ipRGCs) play a crucial role in non-image-forming visual functions. Given their significant loss observed in various ocular degenerative diseases at early stages, this study aimed to assess changes in both the morphology and associated behavioral functions of ipRGCs in mice between 6 (mature) and 12 (late adult) months old. The findings contribute to understanding the preservation of ipRGCs in late adults and their potential as a biomarker for early ocular degenerative diseases.

Methods

Female and male C57BL/6J mice were used to assess the behavioral consequences of aging to mature and old adults, including pupillary light reflex, light aversion, visual acuity, and contrast sensitivity. Immunohistochemistry on retinal wholemounts from these mice was then conducted to evaluate ipRGC dendritic morphology in the ganglion cell layer (GCL) and inner nuclear layer (INL).

Results

Morphological analysis showed that ipRGC dendritic field complexity was remarkably stable through 12 months old of age. Similarly, the pupillary light reflex, visual acuity, and contrast sensitivity were stable in mature and old adults. Although alterations were observed in ipRGC-independent light aversion distinct from the pupillary light reflex, aged wild-type mice continuously showed enhanced light aversion with dilation. No effect of sex was observed in any tests.

Conclusions

The preservation of both ipRGC morphology and function highlights the potential of ipRGC-mediated function as a valuable biomarker for ocular diseases characterized by early ipRGC loss. The consistent stability of ipRGCs in mature and old adult mice suggests that detected changes in ipRGC-mediated functions could serve as early indicators or diagnostic tools for early-onset conditions such as Alzheimer's disease, Parkinson's disease, and diabetes, where ipRGC loss has been documented.

Autonomic nervous system and endocrine system response to upper and lower cervical spine mobilization in healthy male adults: a randomized crossover trial

BACKGROUND

Cervical spine mobilizations may differentially modulate both components of the stress response, consisting of the autonomic nervous system and hypothalamic pituitary adrenal-axis, depending on whether the target location is the upper or lower cervical spine. To date, no study has investigated this.

METHODS

A randomized, crossover trial investigated the effects of upper versus lower cervical mobilization on both components of the stress response simultaneously. The primary outcome was salivary cortisol (sCOR) concentration. The secondary outcome was heart rate variability measured with a smartphone application. Twenty healthy males, aged 21-35, were included. Participants were randomly assigned to block-AB (upper then lower cervical mobilization, n = 10) or block-BA (lower than upper cervical mobilization, n = 10), separated by a one-week washout period. All interventions were performed in the same room (University clinic) under controlled conditions. Statistical analyses were performed with a Friedman's Two-Way ANOVA and Wilcoxon Signed Rank Test.

RESULTS

Within groups, sCOR concentration reduced thirty-minutes following lower cervical mobilization (p = 0.049). Between groups, sCOR concentration was different at thirty-minutes following the intervention (p = 0.018).

CONCLUSION

There was a statistically significant reduction in sCOR concentration following lower cervical spine mobilization, and between-group difference, 30 min following the intervention. This indicates that mobilizations applied to separate target locations within the cervical spine can differentially modulate the stress response.

Assessment of Changes in Physiological Markers in Different Body Fluids at Rest and after Exercise

Physiological and biological markers in different body fluids are used to measure the body’s physiological or pathological status. In the field of sports and exercise medicine, the use of these markers has recently become more popular for monitoring an athlete’s training response and assessing the immediate or long-term effects of exercise. Although the effect of exercise on different physiological markers using various body fluids is well substantiated, no article has undertaken a review across multiple body fluids such as blood, saliva, urine and sweat. This narrative review aims to assess various physiological markers in blood, urine and saliva, at rest and after exercise and examines physiological marker levels obtained across similar studies, with a focus on the population and study methodology used. Literature searches were conducted using PRISMA guidelines for keywords such as exercise, physical activity, serum, sweat, urine, and biomarkers, resulting in an analysis of 15 studies for this review paper. When comparing the effects of exercise on physiological markers across different body fluids (blood, urine, and saliva), the changes detected were generally in the same direction. However, the extent of the change varied, potentially as a result of the type and duration of exercise, the sample population and subject numbers, fitness levels, and/or dietary intake. In addition, none of the studies used solely female participants; instead, including males only or both male and female subjects together. The results of some physiological markers are sex-dependent. Therefore, to better understand how the levels of these biomarkers change in relation to exercise and performance, the sex of the participants should also be taken into consideration.

The effects of intranasal oxytocin on black participants’ responses to outgroup acceptance and rejection

Social acceptance (vs. rejection) is assumed to have widespread positive effects on the recipient; however, ethnic/racial minorities often react negatively to social acceptance by White individuals. One possibility for such reactions might be their lack of trust in the genuineness of White individuals’ positive evaluations. Here, we examined the role that oxytocin—a neuropeptide putatively linked to social processes—plays in modulating reactions to acceptance or rejection during interracial interactions. Black participants (N = 103) received intranasal oxytocin or placebo and interacted with a White, same-sex stranger who provided positive or negative social feedback. After positive feedback, participants given oxytocin (vs. placebo) tended to display approach-oriented cardiovascular responses of challenge (vs. threat), exhibited more cooperative behavior, and perceived the partner to have more favorable attitudes toward them after the interaction. Following negative feedback, oxytocin reduced anger suppression. Oxytocin did not modulate testosterone reactivity directly, but our exploratory analysis showed that the less participants suppressed anger during the interaction with their partner, the greater testosterone reactivity they displayed after the interaction. These results survived the correction for multiple testing with a false discovery rate (FDR) of 20%, but not with a rate of 10 or 5%. Discussion centers on the interplay between oxytocin and social context in shaping interracial interactions.

Diurnal dynamic range as index of dysregulation of system dynamics. A cortisol examplar using data from the Study of Midlife in the United States

We discuss the importance of including measures of dysregulated system dynamics in the operationalization of allostatic load. The concept of allostatic load, as originally proposed by McEwen and Stellar, included dysregulation not only in the resting state of physiological systems, but also in system dynamics. We describe previous work on cortisol diurnal dynamic range (peak to nadir spread) as an index of the health of the hypothalamic-pituitary-adrenal axis, with compression of dynamic range being a marker of dysregulation. In particular, we review the evidence for a) diurnal dynamic range compression in people from disadvantaged backgrounds, b) cross-sectional association of cortisol diurnal dynamic range compression with dysregulation in other systems' resting states, and c) cross-sectional association of cortisol diurnal dynamic range compression with lower scores on cognitive testing. Then, we present new data from the Study of Midlife in the United States (MIDUS) on longitudinal associations of cortisol dynamic range compression with subsequent cognitive decline and all-cause mortality. Briefly, each standard deviation decrement in cortisol diurnal dynamic range is associated with adjusted mortality hazard ratio of 1.35 (95% confidence interval: 1.19, 1.54). Among those who scored at median or lower in executive functioning at baseline and survive, each standard deviation decrement in cortisol dynamic range is associated with 1% greater decline in executive functioning over a decade (95% confidence interval: 0.4%, 2.0%). We conclude that including measures of system dynamics like diurnal dynamic range in the next generation of allostatic load measurement will likely advance understanding of the cumulative physiological burden of chronic stress and life experiences, and improve the prediction of future health consequences.

Pilot Study of the Effects of Bright Ambient Therapy on Dementia Symptoms and Cognitive Function

Light therapy potentially improves dementia symptoms. In this study, we examined the effects of bright light therapy on neuropsychiatric behaviors and cognitive function. Thirty-five participants were assigned to either the experimental or comparison group. The experimental group was exposed to bright light at 2,500 lux, and the comparison group was exposed to 114–307 lux. The instruments used were the Neuropsychiatric Inventory and the Mini-Mental State Examination. The experimental group showed a significant improvement in Neuropsychiatric Inventory scores; these scores, which were calculated using generalized estimating equations with medication (benzodiazepines) as a covariate, were reduced by 65% (P < 0.001) and 78% (P = 0.001) by the 5th and 9th weeks, respectively. At the same time, Mini-Mental State Examination scores increased by 19% (P = 0.007) and 28% (P = 0.04), respectively. However, differences in outcomes between the 5th and 9th weeks were not significant. A 4-week regimen of bright light therapy was the most effective, with higher adherence and acceptability.

Cortisol and Testosterone in Leadership Practice

This study sought to discover whether and how biological parameters can predict leadership behavior in the following leadership-related tasks: a face-to-face negotiation (Study 1), an individual problem-solving case (Study 2), and a group-based problem-solving case (Study 3). We replicated previous work by Mehta, Mor, Yap and Prasad in testing the dual-hormone hypothesis related to testosterone increase and cortisol decrease (Study 1), but our findings do not provide evidence to support the dual-hormone hypothesis. In Study 2, we found that high openness was a significant predictor in the individual problem-solving case. The results from Study 3 indicated that higher openness was related to a better score on the group exercise. Our findings did not support the dual-hormone model, and we did not find support for the seller-specific effect reported in Mehta et al. The original study included 64 participants with complete hormone data, while our replicational study involved 114 participants with complete hormone data.

Melatonin to Rescue the Aged Heart: Antiarrhythmic and Antioxidant Benefits

Aging comes with gradual loss of functions that increase the vulnerability to disease, senescence, and death. The mechanisms underlying these processes are linked to a prolonged imbalance between damage and repair. Damaging mechanisms include oxidative stress, mitochondrial dysfunction, chronodisruption, inflammation, and telomere attrition, as well as genetic and epigenetic alterations. Several endogenous tissue repairing mechanisms also decrease. These alterations associated with aging affect the entire organism. The most devastating manifestations involve the cardiovascular system and may lead to lethal cardiac arrhythmias. Together with structural remodeling, electrophysiological and intercellular communication alterations during aging predispose to arrhythmic events. Despite the knowledge on repairing mechanisms in the cardiovascular system, effective antiaging strategies able to reduce the risk of arrhythmias are still missing. Melatonin is a promising therapeutic candidate due to its pleiotropic actions. This indoleamine regulates chronobiology and endocrine physiology. Of relevance, melatonin is an antiaging, antioxidant, antiapoptotic, antiarrhythmic, immunomodulatory, and antiproliferative molecule. This review focuses on the protective effects of melatonin on age-induced cardiac functional and structural alterations, potentially becoming a new fountain of youth for the heart.

Effects and mechanisms of action of light-emitting diodes on the human retina and internal clock

White light-emitting diodes (LEDs) will likely become the most used lighting devices worldwide in the future because of their very low prices over the course of their long lifespans which can be up to several tens of thousands of hours. The expansion of LED use in both urban and domestic lighting has prompted questions regarding their possible health effects, because the light that they provide is potentially high in the harmful blue band (400-500 nm) of the visible light spectrum. Research on the potential effects of LEDs and their blue band on human health has followed three main directions: 1) examining their retinal phototoxicity; 2) examining disruption of the internal clock, i.e., an out-of-sync clock, in shift workers and night workers, including the accompanying health issues, most concerningly an increased relative risk of cancer; and 3) examining risky, inappropriate late-night use of smartphones and consoles among children and adolescents. Here, we document the recognized or potential health issues associated with LED lighting together with their underlying mechanisms of action. There is so far no evidence that LED lighting is deleterious to human retina under normal use. However, exposure to artificial light at night is a new source of pollution because it affects the circadian clock. Blue-rich light, including cold white LEDs, should be considered a new endocrine disruptor, because it affects estrogen secretion and has unhealthful consequences in women, as demonstrated to occur via a complex mechanism.

Testosterone, cortisol, and secretory immunoglobulin-A within a single day and across two sequential days among trans- and cis-gender men

BACKGROUND

Previous research on the association between testosterone (T) and immunity has produced conflicting results.

OBJECTIVES

We address two potential reasons for these empirical inconsistencies in the present research. First, the association between T and immunity may depend on which branch of the immune system is considered. Here, we examine secretory IgA (sIgA), a measure of mucosal immunity functionally related to respiratory infection risk. Second, the association between T and immunity may depend on a third regulatory variable. Therefore, we examine the interaction between T and cortisol (CORT) as well as their independent and combined effects on mucosal immunity. To do this, we explore intra-individual associations between sIgA, CORT, and T within a single day (i.e., morning vs. evening) and across 2 sequential mornings. We target two samples of men: (1) cisgender (i.e., born and identifying as men), and (2) transgender (i.e., born female but identifying as men) undergoing T therapy for gender realignment.

MATERIALS AND METHODS

One hundred and forty-eight adult men (transgender n = 29) provided saliva samples at three time points: (1) upon waking, (2) before sleep on the same day, and (3) upon waking the following day. Samples were assayed in duplicate for sIgA, T and CORT.

RESULTS

For cisgender men, sIgA, T, and CORT exhibited clear circadian rhythms and were significantly related within and between samples. For transgender men, evidence for circadian change was found for sIgA and CORT, but not T. Further, sIgA was associated with CORT, but not T.

DISCUSSION AND CONCLUSIONS

This study provides the first evidence that salivary T and sIgA concentrations are associated within a single day and across sequential days for cisgender men. Differences between cis- and transgender men suggest that this may only be true for T levels driven by endogenous production; however, future studies should employ a larger sample size.

Hormonal responses in gambling versus alcohol abuse: A review of human studies

The endocrine system plays an essential role in communication between various organs of the body to maintain homeostasis. Both substance use disorders (SUDs) and non-substance abuse disrupt this system and lead to hormonal dysregulations. Here, we focus on the comparison between the function of the endocrine system in gambling disorders and alcohol addiction to understand the commonalities and differences in their neurobiological and psychological underpinnings. We review human research to compare findings on gambling addiction and alcohol dependence pertaining to the dynamic interplay between testosterone and cortisol. Understanding and classifying similarities in hormonal responses between behavioural addiction and SUDs may facilitate development of treatments and therapeutic interventions across different types of addictive disorders, while describing differences may shed light on therapeutic interventions for specific disorders. Although research on gambling addiction is in its infancy, such evaluation may still have a positive effect for addiction research, thereby stimulating discovery of "crossover" pharmacotherapies with benefits for both SUDs and nonsubstance addictions.

Bright Light Therapy and Circadian Cycles in Institutionalized Elders

BACKGROUND

Bright light therapy has been found to be an efficient method to improve the main parameters of circadian rhythms. However, institutionalized elders may suffer reduced exposure to diurnal light, which may impair their circadian rhythms, cognitive performance, and general health status.

OBJECTIVES

To analyze the effects of 5 days of morning exposure for 90 min to bright light therapy (BLT) applied to institutionalized elderly subjects with mild/moderate cognitive impairment.

SUBJECTS

Thirty-seven institutionalized subjects of both sexes, aged 70-93 years.

METHODS

The study lasted three consecutive weeks. During the second week the subjects were submitted to BLT (7000-10,000 lux at eye level) on a daily basis. Cognition, attention, and sleep quality were evaluated at the beginning of the first and third week. Circadian variables were recorded continuously throughout the 3 weeks. Non-invasive holders and validated tests were used to analyze the variables studied.

RESULTS

After BLT we have found significant improvements in general cognitive capabilities, sleep quality and in the main parameters of the subject's circadian rhythms. The results show that merely 90 min of BLT for five days seems to achieve a significant improvement in a constellation of circadian, sleep, health, and cognitive factors.

CONCLUSION

Bright light therapy is an affordable, effective, fast-acting therapy for age-related disturbances, with many advantages over pharmacological alternatives. We hypothesize these effects were the result of activating the residual activity of their presumably weakened circadian system.

Role of Tau Protein in Remodeling of Circadian Neuronal Circuits and Sleep

Multiple neurological, physiological, and behavioral functions are synchronized by circadian clocks into daily rhythms. Neurodegenerative diseases such as Alzheimer's disease and related tauopathies are associated with a decay of circadian rhythms, disruption of sleep patterns, and impaired cognitive function but the mechanisms underlying these alterations are still unclear. Traditional approaches in neurodegeneration research have focused on understanding how pathology impinges on circadian function. Since in Alzheimer's disease and related tauopathies tau proteostasis is compromised, here we sought to understand the role of tau protein in neuronal circadian biology and related behavior. Considering molecular mechanisms underlying circadian rhythms are conserved from Drosophila to humans, here we took advantage of a recently developed tau-deficient Drosophila line to show that loss of tau promotes dysregulation of daily circadian rhythms and sleep patterns. Strikingly, tau deficiency dysregulates the structural plasticity of the small ventral lateral circadian pacemaker neurons by disrupting the temporal cytoskeletal remodeling of its dorsal axonal projections and by inducing a slight increase in the cytoplasmic accumulation of core clock proteins. Taken together, these results suggest that loss of tau function participates in the regulation of circadian rhythms by modulating the correct operation and connectivity of core circadian networks and related behavior.

Revisiting the relationships of 2D:4D with androgen receptor (AR) gene and current testosterone levels: Replication study and meta-analyses

The relationships of digit ratio (2D:4D) with the length of AR (CAG)n, and testosterone levels from saliva and blood have been extensively debated over the years. This research including three studies further clarifies such controversies. To do so, we re-examined the relationships between the length of AR (CAG)n, 2D:4D, and current testosterone levels, through replication study and meta-analysis for each study. The results indicate: (a) the length of AR (CAG)n is not significantly associated with 2D:4D; (b) current testosterone levels are not significantly associated with the ratio; and (c) the length is not significantly associated with testosterone levels. Thus, AR (CAG)n and current testosterone levels are not significantly related to 2D:4D at individual level.

Photosensitive Melanopsin-Containing Retinal Ganglion Cells in Health and Disease: Implications for Circadian Rhythms

Melanopsin-containing retinal ganglion cells (mRGCs) represent a third class of retinal photoreceptors involved in regulating the pupillary light reflex and circadian photoentrainment, among other things. The functional integrity of the circadian system and melanopsin cells is an essential component of well-being and health, being both impaired in aging and disease. Here we review evidence of melanopsin-expressing cell alterations in aging and neurodegenerative diseases and their correlation with the development of circadian rhythm disorders. In healthy humans, the average density of melanopsin-positive cells falls after age 70, accompanied by age-dependent atrophy of dendritic arborization. In addition to aging, inner and outer retinal diseases also involve progressive deterioration and loss of mRGCs that positively correlates with progressive alterations in circadian rhythms. Among others, mRGC number and plexus complexity are impaired in Parkinson's disease patients; changes that may explain sleep and circadian rhythm disorders in this pathology. The key role of mRGCs in circadian photoentrainment and their loss in age and disease endorse the importance of eye care, even if vision is lost, to preserve melanopsin ganglion cells and their essential functions in the maintenance of an adequate quality of life.

Tandem Androgenic and Psychological Shifts in Male Reproductive Effort Following a Manipulated "Win" or "Loss" in a Sporting Competition

Male-male competition is involved in inter- and intrasexual selection, with both endocrine and psychological factors presumably contributing to reproductive success in human males. We examined relationships among men's naturally occurring testosterone, their self-perceived mate value (SPMV), self-esteem, sociosexuality, and expected likelihood of approaching attractive women versus situations leading to child involvement. We then monitored changes in these measures in male rowers (N = 38) from Cambridge, UK, following a manipulated "win" or "loss" as a result of an indoor rowing contest. Baseline results revealed that men with heightened testosterone and SPMV values typically had greater inclinations toward engaging in casual sexual relationships and a higher likelihood of approaching attractive women in a hypothetical social situation. As anticipated, both testosterone and SPMV increased following a manipulated "victory" and were associated with heightened sociosexuality, and increased expectations toward approaching attractive women versus individuals who would involve them in interacting with children after the race. SPMV and self-esteem appeared to mediate some of the effects of testosterone on post-race values. These findings are considered in the broader context of individual trade-offs between mating and parental effort and a model of the concurrent and dynamic androgenic and psychological influences contributing to male reproductive effort and success.

Exploring the Effect of Attachment Styles and Winning or Losing a Status Contest on Testosterone Levels

A person’s ability to form relationships and seek and attain social status affects their chances of survival. We study how anxious and avoidant-attachment styles and subsequent winning or losing affects the testosterone (T) levels of team members playing two status contests. The first is a management game played by teams striving to earn the most profits. Winners and losers emerge due to the cognitive endeavor of the players, which provokes intense status dynamics. Avoidant-attached winners do not show higher T levels whereas anxious-attached winners do. The second is an economic game which is rigged and favors some teams to become richer than others; teams have the option though to trade with each other and reduce the self-perpetuating rich-poor dynamics embedded in the game. Besides attachment styles, we here also explore how authentic pride as a self-conscious emotion affects team members’ T levels as players trade with others to create more fairness. As in the first status contest, players’ T levels are not significantly affected by their avoidant attachment style, neither as a main effect nor in interaction with winning or losing the game. However, similar to the first game, players’ anxious attachment style affects their T levels: anxious-attached players generate significantly higher T levels when winning the game, but only when experiencing high authentic pride during the game. In short, the moderating effects of attachment style on winners’ T levels are partly replicated in both status games which allows us to better understand the functioning of working models of attachment styles during and after status contests and gives us a better understanding of working models of attachment styles in general.

When anger expression might be beneficial for African Americans: The moderating role of chronic discrimination

OBJECTIVES

Anger expression is assumed to have mostly negative health effects. Yet, evidence is mixed on how anger expression influences African Americans' cardiovascular health. The present research aimed to clarify this link by examining moderating effects of chronic discrimination on the relationship between anger expression and cardiovascular risk among African Americans in experimental (Study 1) and epidemiological (Study 2) studies.

METHOD

Study 1 examined how African Americans' trait anger expression was linked to (a) physiologic reactivity to acute social rejection during an interracial encounter (Session 1); and (b) total/HDL cholesterol assessed two months later (Session 2). Study 2 examined the relationship between anger expression and total/HDL cholesterol with a larger sample of African Americans from the Midlife in the United States (MIDUS) survey. Both studies examined perceptions of chronic discrimination as a moderator of the relationships between anger expression and biological responses.

RESULTS

In Study 1 higher anger expression was associated with quicker cortisol recovery and greater testosterone reactivity following outgroup social rejection in Session 1 and lower total/HDL cholesterol in Session 2. Study 2 replicated the relationship between anger expression and lower total/HDL cholesterol and further showed that this relationship was unique to the expressive aspect of anger. Importantly, in both studies, these potentially beneficial effects of anger expression were only evident among individuals with lower perceptions of chronic discrimination.

CONCLUSIONS

These findings suggest that anger expression, when coupled with low levels of chronic discrimination, is associated with adaptive patterns of physiologic responses among African Americans. (PsycINFO Database Record

Stress and cortisol responses in men: differences according to facial symmetry

Stress response is associated with increased activity in the hypothalamic-pituitary-adrenocortical axis. Chronic stress-induced elevation in cortisol may alter its own negative regulation with multiple long-term consequences for physical and psychological health. One of the most reliable physical traits associated with mental, apparent physical health, and competitiveness is the degree of facial fluctuating asymmetry. However, to our knowledge there are no studies regarding the relationship between cortisol levels, facial symmetry and male competitiveness, and how cortisol changes after a stressful test depending on these traits. Here, a group of 100 college men were photographed to obtain their facial asymmetry levels. They then, answered the perceived stress scale and the intrasexual competition test and donated two saliva samples (pre-and post-test sample) to measure the change in their cortisol levels after a stressful test. We found that basal cortisol levels were positively correlated with both perceived stress and competitiveness, but not with facial fluctuating asymmetry. Cortisol levels increased in most symmetrical men after a short stressful test, but it decreased in most asymmetrical men. The results suggest differences in endocrine responses according to facial fluctuating asymmetry in men and how these responses could be related to the maintenance of social status.

Neuroendocrine Response Following a Thoracic Spinal Manipulation in Healthy Men

Study Design Controlled laboratory study. Background Spinal manipulation (SM) can trigger a cascade of responses involving multiple systems, including the sympathetic nervous system and the endocrine system, specifically, the hypothalamic-pituitary axis. However, no manual therapy study has investigated the neuroendocrine response to SM (ie, sympathetic nervous system-hypothalamic-pituitary axis) in the same trial. Objective To determine short-term changes in sympathetic nervous system activity, heart rate variability, and endocrine activity (cortisol, testosterone, and testosterone-cortisol [T/C] ratio) following a thoracic SM. Methods Twenty-four healthy men aged between 18 and 45 years were randomized into 2 groups: thoracic SM (n = 12) and sham (n = 12). Outcome measures were salivary cortisol (micrograms per deciliter), salivary testosterone (picograms per milliliter), T/C ratio, heart rate variability, and changes in oxyhemoglobin concentration of the right calf muscle (micromoles per liter). Measurements were done before and at 5 minutes, 30 minutes, and approximately 6 hours after intervention. Results A statistically significant group-by-time interaction was noted for T/C ratio (P<.05) and salivary cortisol (P<.01) concentrations. Significant between-group differences were noted for salivary cortisol concentration at 5 minutes (mean difference, 0.35; 95% confidence interval: 0.12, 0.6; interaction: P<.01) and for T/C ratio at 6 hours postintervention (mean difference, -0.09; 95% confidence interval: -0.16, -0.04; P = .02). However, SM did not differentially alter oxyhemoglobin, testosterone, or heart rate variability relative to responses in the sham group. Conclusion Thoracic SM resulted in an immediate decrease in salivary cortisol concentration and reduced T/C ratio 6 hours after intervention. A pattern of immediate sympathetic excitation was also observed in the SM group. J Orthop Sports Phys Ther 2017;47(9):617-627. Epub 13 Jul 2017. doi:10.2519/jospt.2017.7348.

Preliminary evidence that acute stress moderates basal testosterone's association with retaliatory behavior

A contribution to a special issue on Hormones and Human Competition. Testosterone is theorized to increase retaliation after social provocation. However, empirical evidence in support of these theories is mixed. The present research investigated whether acute stress causally suppresses testosterone's association with retaliation. We also explored sex differences in behavioral responses to acute stress. Thirty-nine participants (51.28% male) were randomly assigned to a high- or low-stress condition. Then participants engaged in 20 one-shot rounds of the ultimatum game, which was used to assess retaliatory behavioral responses to unfair treatment. Participants provided two saliva samples to measure testosterone and cortisol concentrations - one sample before the stress manipulation, and the second after the ultimatum game (20minutes post-stressor). Results revealed a positive association between basal testosterone and retaliation in the low-stress condition, but not in the high-stress condition. Further, cortisol concentrations increased in the high- compared to the low-stress condition, and these cortisol changes moderated the association between basal testosterone and retaliation. The associations between basal testosterone and retaliation under varying levels of stress were similar in men and women. However, there was a sex difference in behavioral responses to the stress manipulation that was independent of testosterone. In women, the high-stress condition reduced retaliation compared to the low-stress condition, whereas in men the opposite pattern emerged. Collectively, this study (i) provides preliminary evidence that experimentally manipulated stress blocks basal testosterone's association with retaliation, and (ii) reveals a sex difference in retaliation under varying levels of stress. Discussion focuses on mechanisms, limitations, and the need for follow-up studies with larger sample sizes.

Neurodegeneration and the Circadian Clock

Despite varied etiologies and symptoms, several neurodegenerative diseases—specifically, Alzheimer’s (AD), Parkinson’s (PD), and Huntington’s diseases (HDs)—share the common feature of abnormal circadian rhythms, such as those in behavior (e.g., disrupted sleep/wake cycles), physiological processes (e.g., diminished hormone release) and biochemical activities (e.g., antioxidant production). Circadian disturbances are among the earliest symptoms of these diseases, and the molecular mechanisms of the circadian system are suspected to play a pivotal, and possibly causal, role in their natural histories. Here, we review the common circadian abnormalities observed in ADs, PDs and HDs, and summarize the evidence that the molecular circadian clockwork directly influences the course of these disease states. On the basis of this research, we explore several circadian-oriented interventions proposed as treatments for these neurological disorders.

Moderating Effects of Cortisol on Neural-Cognitive Association in Cognitively Normal Elderly Subjects

Cortisol homeostasis is important for healthy brain and cognitive aging. The aim of the current study is to investigate the role of serum cortisol levels in the relationship between regional brain volumes and cognitive processing speed in a group of cognitively normal elderly subjects. Forty-one healthy elderly participants were from a parallel longitudinal study. The reported data in this study reflects baseline measurements. Whole-brain anatomical scanning was performed using a 3.0 Tesla Philips Medical Systems Achieva scanner. Cognitive processing speed was assessed by the digit-symbol and symbol search tests, from the Chinese version of the Wechsler Adult Intelligence Scale—third edition (WAIS-III). Serum cortisol levels (sampled in the late morning) were measured by ELISA kits. Whole-brain regression analysis revealed that serum cortisol levels positively predicted the white matter volumes (WMV) of the right thalamus, the gray matter volumes (GMV) of the left thalamus and right cerebellar tonsil, and negatively predicted the WMV and GMV of the left middle temporal gyrus (MTG) in 41 healthy elderly participants. Furthermore, serum cortisol significantly moderated the relationship between the GMV of the left MTG and processing speed, as well as the GMV of the left thalamus and processing speed. This study provided the first piece of evidence supporting serum cortisol levels in moderating the relationship between regional brain volumes and processing speed in healthy elderly subjects. This observation enriches our understanding of the role of cortisol in brain morphology and cognitive functioning.

The aging clock: circadian rhythms and later life

Circadian rhythms play an influential role in nearly all aspects of physiology and behavior in the vast majority of species on Earth. The biological clockwork that regulates these rhythms is dynamic over the lifespan: rhythmic activities such as sleep/wake patterns change markedly as we age, and in many cases they become increasingly fragmented. Given that prolonged disruptions of normal rhythms are highly detrimental to health, deeper knowledge of how our biological clocks change with age may create valuable opportunities to improve health and longevity for an aging global population. In this Review, we synthesize key findings from the study of circadian rhythms in later life, identify patterns of change documented to date, and review potential physiological mechanisms that may underlie these changes.

Diurnal testosterone variability is differentially associated with parenting quality in mothers and fathers

Previous studies on the relation between testosterone (T) levels and parenting have found ample evidence for the challenge hypothesis, demonstrating that high T levels inhibit parental involvement and that becoming a parent is related to a decrease in T levels in both mothers and fathers. However, less is known about the relation between T levels and more qualitative aspects of parenting. In the current study we examined basal T levels and diurnal variability in T levels in relation to mothers' and fathers' parenting quality. Participants included 217 fathers and 124 mothers with two children (3 and 5years of age). Evening and morning salivary T samples were analyzed with radio-immunoassays to determine circulating T levels. Parental sensitivity (i.e., child-centered responsiveness) and respect for children's autonomy were observed during free play in the family home. The results showed that higher evening T levels in mothers were associated with more sensitivity to the oldest and youngest child. Diurnal T variability was more consistently associated with parenting behavior towards their children than basal T levels. For fathers, more diurnal variability in T was associated with more sensitivity and more respect for autonomy with their youngest children. For mothers, more diurnal variability in T was associated with less sensitivity to both children and less respect for the youngest child's autonomy. These findings suggest that the T system might act differently in relation to parenting behavior in males and females.

Circadian system - A novel diagnostic and therapeutic target in Parkinson's disease?

The circadian system regulates biological rhythmicity in the human body. The role of the circadian system in neurological disorders is a theme that is attracting an increasing amount of interest from the scientific community. This has arisen, in part, from emerging evidence that disorders such as Parkinson's disease (PD) are multifactorial with many features exhibiting diurnal fluctuations, thereby suggestive of circadian involvement. Although the importance of fluctuating motor and nonmotor manifestations in PD have been well acknowledged, the role of the circadian system has received little attention until recently. It is proposed that intervening with circadian function provides a novel research avenue down which new strategies for improving symptomatic treatment and slowing of the progressive degenerative process can be approached to lessen the burden of PD. In this article we review the literature describing existing circadian research in PD and its experimental models.

Peripheral Circadian Clocks Mediate Dietary Restriction-Dependent Changes in Lifespan and Fat Metabolism in Drosophila

Endogenous circadian clocks orchestrate several metabolic and signaling pathways that are known to modulate lifespan, suggesting clocks as potential targets for manipulation of metabolism and lifespan. We report here that the core circadian clock genes, timeless (tim) and period (per), are required for the metabolic and lifespan responses to DR in Drosophila. Consistent with the involvement of a circadian mechanism, DR enhances the amplitude of cycling of most circadian clock genes, including tim, in peripheral tissues. Mass-spectrometry-based lipidomic analysis suggests a role of tim in cycling of specific medium chain triglycerides under DR. Furthermore, overexpression of tim in peripheral tissues improves its oscillatory amplitude and extends lifespan under ad libitum conditions. Importantly, effects of tim on lifespan appear to be mediated through enhanced fat turnover. These findings identify a critical role for specific clock genes in modulating the effects of nutrient manipulation on fat metabolism and aging.

Circadian Characteristics of Older Adults and Aerobic Capacity

BACKGROUND

Alteration of circadian rhythmicity with aging might depend on physical aerobic capacity.

METHODS

Three groups of participants were established based on their peak oxygen consumption (Group 1 < 20mL/min/kg; Group 2 > 20mL/min/kg and <30mL/min/kg; Group 3 > 30mL/min/kg). Each participant had an individual evaluation of their circadian rhythmicity characteristics through two well-known circadian rhythms: core temperature and rest/activity cycles. Nocturnal sleep was also recorded using actimetry and diurnal vigilance tested in a car driving simulator.

RESULTS

The amplitude of the oral temperature fluctuations for Group 1 is significantly lower (p < .05) than that of Group 3. Group 2 (p < .01) and Group 3 (p < .05) were significantly more active during the day than Group 1. The index of inactivity during the night for Groups 2 (p < .05) and 3 (p < .01) was higher than Group 1. Results of the car driving simulation showed that for Group 1, the number of lane crossings was significantly higher than Groups 2 (p < .01) and 3 (p < .01). In addition, diurnal vigilance was lower in Group 1.

CONCLUSIONS

The biological clock seems to be enhanced in older participants with a higher level of physical capacity.

Can the neural-cortisol association be moderated by experience-induced changes in awareness?

Cortisol homeostasis is important for cognitive and affective functions that depend on cortisol-sensitive brain regions including the hippocampus and prefrontal cortex. Recent studies have shown that training induces changes in the brain. We report the findings of a longitudinal study that verified the moderation effect of experience-induced changes in awareness on the neural-cortisol association in cortisol-sensitive brain regions. These findings provide the first piece of evidence that planned behavioral experience can moderate the neural-cortisol association. A range of changes in awareness was achieved in a sample of 21 Chinese participants, divided into two groups: Awareness-based compassion meditation (ABCM) (n = 10) and relaxation (n = 11). We observed that changes in awareness were significant moderators of hippocampal-cortisol changes. Furthermore, a significant negative association between changes in plasma cortisol level and the resting-state synchrony of the right hippocampal and insular-frontal-operculum regions was observed. These novel findings shed light on the inter-relationships between changes in hippocampal-cortisol levels and changes in awareness and preliminarily identify the neural underpinnings of interventions for cortisol-related abnormal functioning for further study.

Consequences of Circadian Disruption on Neurologic Health

Circadian rhythms have a major role in physiology and behavior. Circadian disruption has negative consequences for physiologic homeostasis at molecular, cellular, organ-system, and whole-organism levels. The onset of many cerebrovascular insults shows circadian temporal trends. Impaired sleep-wake cycle, the most robust output rhythms of the circadian system, is significantly affected by neurodegenerative disorders, may precede them by decades, and may also affect their progression. Emerging evidence suggests that circadian disruption may be a risk factor for these neurologic disorders. This article discusses the implications of circadian rhythms in brain disorders, with an emphasis on cerebrovascular and neurodegenerative disorders.

Beneficial effect of melatonin treatment on age-related insulin resistance and on the development of type 2 diabetes

Abstract This paper will review the effect of aging on glucose metabolism and insulin resistance in pancreas and in peripheral tissues and how melatonin administration could affect these parameters. In SAMP8 mice insulin levels in plasma were found to be increased together with enhanced HOMA-IR values, whereas insulin content in pancreas showed a decrease with aging. Aging in SAMP8 mice was also associated with a significant increase in the relative expression of both protein and mRNA of different pro-inflammatory mediators. Furthermore, aging was associated with a decrease in the expression of Pdx-1, FoxO 1 and FoxO 3A and Sirt 1 in pancreas SAMP8 samples. Melatonin administration was able to reduce these age-related alterations, decreasing plasma insulin levels and increasing its pancreatic content in SAMP8 mice. HOMA-IR was decreased with melatonin treatment in all animals. Conversely, in SAMP8 mice, melatonin treatment decreased the expression of glucagon, GLUT2, somatostatin and insulin. Furthermore it was also able to increase the expression of Sirt 1, Pdx-1 and FoxO 3A. The present study has shown that aging is associated with significant alterations in the relative expression of pancreatic genes involved in both insulin secretion and glucose metabolism and that these are associated with an increase in inflammation and oxidative stress. Melatonin administration was able to reduce oxidative stress and inflammation and thus to improve pancreatic function in old mice. By doing so, insulin resistance is diminished and plasma insulin is reduced, enhancing insulin pancreatic content and reducing plasma glucose levels and HOMA index.

Buying time: a rationale for examining the use of circadian rhythm and sleep interventions to delay progression of mild cognitive impairment to Alzheimer's disease

As of 2010, the worldwide economic impact of dementia was estimated at $604 billion USD; and without discovery of a cure or effective interventions to delay disease progression, dementia's annual global economic impact is expected to surpass $1 trillion USD as early as 2030. Alzheimer's disease (AD) is the leading cause of dementia accounting for over 75% of all cases. Toxic accumulation of amyloid beta (Aβ), either by overproduction or some clearance failure, is thought to be an underlying mechanism of the neuronal cell death characteristic of AD-though this amyloid hypothesis has been increasingly challenged in recent years. A compelling alternative hypothesis points to chronic neuroinflammation as a common root in late-life degenerative diseases including AD. Apolipoprotein-E (APOE) genotype is the strongest genetic risk factor for AD: APOE-ε4 is proinflammatory and individuals with this genotype accumulate more Aβ, are at high risk of developing AD, and almost half of all AD patients have at least one ε4 allele. Recent studies suggest a bidirectional relationship exists between sleep and AD pathology. Sleep may play an important role in Aβ clearance, and getting good quality sleep vs. poor quality sleep might reduce the AD risk associated with neuroinflammation and the ε4 allele. Taken together, these findings are particularly important given the sleep disruptions commonly associated with AD and the increased burden disrupted sleep poses for AD caregivers. The current review aims to: (1) identify individuals at high risk for dementia who may benefit most from sleep interventions; (2) explore the role poor sleep quality plays in exacerbating AD type dementia; (3) examine the science of sleep interventions to date; and (4) provide a road map in pursuit of comprehensive sleep interventions, specifically targeted to promote cognitive function and delay progression of dementia.

Melatonin and the Charlson Comorbidity Index (CCI): the Treviso Longeva (Trelong) study

INTRODUCTION

It has been reported that elderly subjects have a compromised ability to produce melatonin nightly, and that reduced melatonin levels may be a risk factor for cancer. The purpose of this study was to evaluate the relationship between melatonin levels and chronic diseases in a cohort of elderly subjects using the Charlson comorbidity index (CCI).

DESIGN

We performed a secondary data analysis of a longitudinal study of a representative, age-stratified, sample population.

SETTING

The Treviso Longeva (Trelong) study, in Treviso, Italy.

PARTICIPANTS

A total of 114 men and 146 women, aged 77 years and older, still alive after 7 years of follow-up.

MEASUREMENTS

As an estimation of serum melatonin secretion levels, urinary 6-sulfatoxymelatonin (aMT6s) was assayed in the urine of 260 elderly subjects using an enzyme-linked immunosorbent assay (ELISA) kit (product 01-EK-M6S, ALPCO Immunoassays, Windham, NH). All aMT6s levels were creatinine standardized ([aMT6s]/[creatinine]), and the CCI was calculated.

RESULTS

The melatonin levels decreased with aging despite not reaching statistical significance, and the decrease was more evident in males than in females (40.5 ng vs 47.0 ng aMT6s/mg creatinine, ns). Melatonin levels were significantly lower in patients reporting insomnia (p=0.05). The CCI score was inversely correlated with the levels of melatonin (p=0.03). Melatonin levels of subjects affected by CCI pathologies were significantly lower than those of healthy subjects (p=0.03) and of subjects suffering from diseases not included in the CCI and, therefore, less severe (p=0.03).

CONCLUSION

Melatonin appears to be a marker of disease state and severity, as well as of sleep disorders, in the elderly. These early findings would confirm the protective role of melatonin against several chronic diseases. The benefits of this agent as a possible medication should be more thoroughly clinically tested.

Changes in serum free testosterone, sleep patterns, and 5-alpha-reductase type I activity influence changes in sebum excretion in female subjects

BACKGROUND/PURPOSE

Sebum is thought to play an important role in acne vulgaris and sebum excretion rate (SER) is often used as a marker of efficacy in acne studies. This study explored factors that could induce intra-subject variability in SER.

METHODS

SER was measured twice, 7 days apart, on the forehead of 40 healthy subjects. At each visit, the following parameters were also evaluated: serum androgen levels, 5-alpha-reductase type I gene expression, forehead temperature, sleep habits, diet, facial washing routine, and UV exposure.

RESULTS

There was a positive correlation between the time subjects fell asleep on Day 0 and the change in SER for the left (P = 0.010; R = 0.402) and right sides (P = 0.002; R = 0.467) of the forehead. There was a significant inverse correlation between SER and 5-alpha-reductase type 1 expression and between free testosterone levels and 5-alpha-reductase type 1 expression. In sub-analyses performed on men and women, these correlations were only significant for women.

CONCLUSION

Variations in sleep patterns, free testosterone, and 5-alpha-reductase type 1 activity are associated with changes in sebum excretion in women. This could explain some of the inter-subject variability in SER measured between visits in clinical studies.

Sleep-wake cycle in young and older persons with a lifetime history of mood disorders

Considering the marked changes in sleep and circadian rhythms across the lifespan, age may contribute to the heterogeneity in sleep-wake profiles linked to mood disorders. This study aimed to investigate the contributions of age and depression severity to sleep-wake disturbances. The Hamilton Depression Rating Scale (HDRS) was administered to assess current symptoms severity in 238 persons with a history of a mood disorder between 12 and 90 years of age (y.o.). Actigraphy was recorded over five to 22 days. Regression analyses and analyses of variance [age (12–19 y.o., 20–39 y.o., 40–59 y.o., and ≥60 y.o.) by depression severity (HDRS< and ≥8)] were conducted. The 12–19 y.o. and 20–39 y.o. groups had a delayed sleep schedule and acrophase compared to all other groups. The ≥60 y.o. group had a lower rhythmicity and amplitude (p≤.006) than the 12–19 y.o. group (p≤.046). Participants with a HDRS≥8 spent longer time in bed, had later sleep offset times and had lower circadian rhythmicity than those with a HDRS<8 (p≤.036). Younger age and higher HDRS score correlated with later sleep onset and offset times, longer time in bed, higher WASO, lower sleep efficiency and later acrophase (p≤.023). Age was a significant predictor of delayed sleep and activity schedules (p≤.001). The profile of sleep-wake cycle disturbances associated with mood disorders changes with age, with prominent sleep phase delay during youth and reduced circadian strength in older persons. Conversely, disruptions in sleep consolidation seem more stable across age.

Daytime trajectories of cortisol: demographic and socioeconomic differences--findings from the National Study of Daily Experiences

Cortisol's daytime rhythm is thought to be altered by aging and by exposure to chronic stress. However, measurement of an individual's usual cortisol rhythm is hampered by the effects of acute stressors, by differences between working days and weekends, by between-day variation in waking time and sleep duration, by variability in cortisol sampling times, and by possible variability in the timing of cortisol peak and nadir. Therefore, to determine differences in the usual daytime cortisol rhythm by age, socioeconomic status, and race/ethnicity, we measured salivary cortisol levels at four time-points, repeated over four days that included both weekdays and weekend days, in 1693 men and women from a national sample, and used three alternate growth curve specifications for the underlying cortisol rhythm (linear spline, quadratic spline, piece-wise linear-cubic) in order to minimize the impact of sample timing and other methodological issues. Model-predicted mean values of (and demographic and socioeconomic differences in) cortisol peak, nadir, and area under the curve (AUC) were nearly identical across model specifications. Older age and male gender were independently associated with higher cortisol peak, nadir, and AUC. Low education and minority race/ethnicity status were independently associated with lower cortisol peak and higher nadir, but were not associated with AUC. We also found significant cortisol peak and AUC associations with waking time, sleep duration, and workday vs. weekend day status, suggesting the importance of measuring these confounders and of collecting cortisol measurements over multiple days in research studies. We conclude that daytime cortisol levels are higher in older age and in men compared to women, and that the daytime cortisol rhythm is flatter (more blunted) in less privileged segments of society. Flattening of daytime cortisol rhythms may represent one mechanism by which social stressors lead to poor health outcomes.

Morning and evening exercise

A growing body of evidence suggests that exercise may contribute to preventing pathological changes, treating multiple chronic diseases, and reducing mortality and morbidity ratios. Scientific evidence moreover shows that exercise plays a key role in improving health-related physical fitness components and hormone function. Regular exercise training is one of the few strategies that has been strictly adapted in healthy individuals and in athletes. However, time-dependent exercise has different outcomes, based on the exercise type, duration, and hormone adaptation. In the present review, we therefore briefly describe the type, duration, and adaptation of exercise performed in the morning and evening. In addition, we discuss the clinical considerations and indications for exercise training.

Potency of melatonin in living beings

Living beings are surrounded by various changes exhibiting periodical rhythms in environment. The environmental changes are imprinted in organisms in various pattern. The phenomena are believed to match the external signal with organisms in order to increase their survival rate. The signals are categorized into circadian, seasonal, and annual cycles. Among the cycles, the circadian rhythm is regarded as the most important factor because its periodicity is in harmony with the levels of melatonin secreted from pineal gland. Melatonin is produced by the absence of light and its presence displays darkness. Melatonin plays various roles in creatures. Therefore, this review is to introduce the diverse potential ability of melatonin in manifold aspects in living organism.

Melatonin can improve insulin resistance and aging-induced pancreas alterations in senescence-accelerated prone male mice (SAMP8)

The aim of the present study was to investigate the effect of aging on several parameters related to glucose homeostasis and insulin resistance in pancreas and how melatonin administration could affect these parameters. Pancreas samples were obtained from two types of male mice models: senescence-accelerated prone (SAMP8) and senescence-accelerated-resistant mice (SAMR1). Insulin levels in plasma were increased with aging in both SAMP8 and SAMR1 mice, whereas insulin content in pancreas was decreased with aging in SAMP8 and increased in SAMR1 mice. Expressions of glucagon and GLUT2 messenger RNAs (mRNAs) were increased with aging in SAMP8 mice, and no differences were observed in somatostatin and insulin mRNA expressions. Furthermore, aging decreased also the expressions of Pdx-1, FoxO 1, FoxO 3A and Sirt1 in pancreatic SAMP8 samples. Pdx-1 was decreased in SAMR1 mice, but no differences were observed in the rest of parameters on these mice strains. Treatment with melatonin was able to decrease plasma insulin levels and to increase its pancreatic content in SAMP8 mice. In SAMR1, insulin pancreatic content and plasma levels were decreased. HOMA-IR was decreased with melatonin treatment in both strains of animals. On the other hand, in SAMP8 mice, treatment decreased the expression of glucagon, GLUT2, somatostatin and insulin mRNA. Furthermore, it was also able to increase the expression of Sirt1, Pdx-1 and FoxO 3A. According to these results, aging is associated with significant alterations in the relative expression of pancreatic genes associated to glucose metabolism. This has been especially observed in SAMP8 mice. Melatonin administration was able to improve pancreatic function in old SAMP8 mice and to reduce HOMA-IR improving their insulin physiology and glucose metabolism.

Crosstalk between the circadian clock circuitry and the immune system

Various features, components, and functions of the immune system present daily variations. Immunocompetent cell counts and cytokine levels present variations according to the time of day and the sleep-wake cycle. Moreover, different immune cell types, such as macrophages, natural killer cells, and lymphocytes, contain a circadian molecular clockwork. The biological clocks intrinsic to immune cells and lymphoid organs, together with inputs from the central pacemaker of the suprachiasmatic nuclei via humoral and neural pathways, regulate the function of cells of the immune system, including their response to signals and their effector functions. Consequences of this include, for example, the daily variation in the response to an immune challenge (e.g., bacterial endotoxin injection) and the circadian control of allergic reactions. The circadian-immune connection is bidirectional, because in addition to this circadian control of immune functions, immune challenges and immune mediators (e.g., cytokines) were shown to have strong effects on circadian rhythms at the molecular, cellular, and behavioral levels. This tight crosstalk between the circadian and immune systems has wide-ranging implications for disease, as shown by the higher incidence of cancer and the exacerbation of autoimmune symptoms upon circadian disruption.

The effect of training at a specific time of day: a review

This article focuses on physical performances after training at a specific time of day. To date, although the effect of time of day on aerobic performances appears to be equivocal, during anaerobic exercises, the effect of time of day has been well established with early morning nadirs and peak performances in the late afternoon. These diurnal rhythms can be influenced by several factors such as the regular training at a specific time of day. Indeed, regular training in the morning hours may increase the lower morning performances to the same or even higher level as their normal diurnal peak typically observed in the late afternoon by a greater increase of performance in the evening. However, regular training in the evening hours may increase the morning-evening (i.e., amplitude of the rhythm) difference by a greater increase of performance in the late afternoon. Therefore, adaptations to training are greater at the time of day at which training is regularly performed than at other times. Nevertheless, although modifications in resting hormones concentrations could explain this time-of-day specific adaptations, precise information on the underlying mechanisms is lacking.