Circadian clocks play a key role in metabolic homeostasis, and disruption of circadian rhythms is inextricably intertwined with metabolic disorders [1]. Emerging evidence in the literature suggests that polyphenols possess the potential to modulate metabolic processes associated with circadian rhythms. This review aims to evaluate the effects of polyphenols on metabolic homeostasis via circadian rhythms and their potential mechanism(s) of action on circadian rhythmicity of clock components and linked metabolic processes, by critically assessing the literature on mammalian cells in vitro. To ensure that all relevant studies in this area were included, a systematic search protocol was developed by defining the inclusion and exclusion criteria based on the population, intervention, comparator and outcome framework, along with limiting the source of evidence to original research written in English. Three databases (Ovid Medline, Web of Science, and Scopus) were searched with no time constraints. The search identified 5842 studies and, after duplicate removal and initial screening, 48 studies were reviewed in full. Of those, 38 were eligible for inclusion. The included studies were published between 2008-2023, with a notable surge in publications after 2016, which is indicative of the growing attention towards polyphenols and circadian biology. 33 polyphenols were examined for their effects on circadian cellular processes (n = 16 papers), expression of clock genes and/or proteins (n = 26), or circadian rhythm features of clock genes (n = 10). A handful of studies examined the role of polyphenols in regulating disrupted glucose and lipid metabolism through clock components. The findings suggested that the underlying mechanisms were BMAL1-dependent. It must be noted that the effects of the reported polyphenols were elucidated at concentrations exceeding the normal range found in human plasma and target tissues (˃ 10 μM). However, a single study revealed that (−)-epigallocatechin-3-gallate (EGCG) at a physiologically-relevant concentration (10 μM), improved hepatic glucose metabolism [2]. Further, the polyphenols reported in this review exhibited the potential to influence numerous clock components, mainly BMAL1, PER2 and RORα/γ, at mRNA and/or protein levels when administered at physiologically-relevant concentrations. These polyphenols include nobiletin, tangeretin, curcumin, bavachalcone, cinnamic acid, (−)-epigallocatechin-3-gallate, resveratrol and Urolithin A. Polyphenols have the potential to regulate circadian oscillators and associated metabolic processes in various types of cells. However, there is significant methodological heterogeneity among the studies, which makes it difficult to compare outcomes. Thus, this review will help future research in the field of circadian impacts of polyphenols to integrate standardised approaches, in aspects such as utilisation of a synchronisation method and physiologically-relevant concentrations of polyphenols (≤ 10 μM) in cultured cells. This is critical for understanding how polyphenols might modulate circadian-metabolic health in humans.

Circadian rhythms are timekeeping mechanisms responsible for an array of biological processes. Disruption of such cycles can detrimentally affect animal health. Circadian rhythms are critical in the co-evolution of host–parasite systems, as synchronization of parasite rhythms to the host can influence infection dynamics and transmission potential. This study examines the circadian rhythms in behaviour and activity of a model fish species (Poecilia reticulata) in isolation and in shoals, both when uninfected and infected with an ectoparasite (Gyrodactylus turnbulli). Additionally, the rhythmical variance of parasite activity under different light conditions as well as rhythmical variance in parasite transmissibility was explored. Overall, infection alters the circadian rhythm of fish, causing nocturnal restlessness. Increased activity of gyrodactylids on the host's skin at night could potentially contribute to this elevated host activity. Whilst migration of gyrodactylids across the host's skin may have caused irritation to the host resulting in nocturnal restlessness, the disruption in guppy activity rhythm caused by the expression of host innate immunity cannot be excluded. We discuss the wider repercussions such behavioural responses to infection have for host health, the implications for animal behaviour studies of diurnal species as well as the application of chronotherapeutic approaches to aquaculture.

This exploratory study investigated the effects of early v. delayed time-restricted eating (TRE) plus caloric restriction (CR) on body weight, body composition and cardiometabolic parameters in adults with overweight and obesity. Adults (20–40 years) were randomised to one of three groups for 8 weeks: early time-restricted eating (eTRE; 08.00–16.00) plus CR, delayed time-restricted eating (dTRE; 12.00–20.00) plus CR or only CR (CR; 08.00–20.00). All groups were prescribed a 25 % energy deficit relative to daily energy requirements. Thirteen participants completed the study in the eTRE and CR groups and eleven in the dTRE group (n 37). After the interventions, there was no significant difference between the three groups for any of the outcomes. Compared with baseline, significant decreases were observed in the body weight (eTRE group: −4·2 kg; 95 % CI, −5·6, −2·7; dTRE group: −4·8 kg; 95 % CI, −5·9, −3·7; CR: −4·0 kg; 95 % CI, −5·9, −2·1), fat mass (eTRE group: −2·9 kg; 95 % CI, −3·9, −1·9; dTRE group: −3·6 kg; 95 % CI, −4·6, −2·5; CR: −3·1 kg; 95 % CI, −4·3, −1·8) and fasting glucose levels (eTRE group: −4 mg/dl; 95 % CI, −8, −1; dTRE group: −2 mg/dl; 95 % CI, −8, 3; CR: −3 mg/dl; 95 % CI, −8, 2). In a free-living setting, TRE with a energetic deficit, regardless of the time of day, promotes similar benefits in weight loss, body composition and cardiometabolic parameters. However, given the exploratory nature of our study, further investigation is needed to confirm these findings.

Accumulative evidence indicates that meal timing is associated with cardiometabolic risks by deteriorating circadian rhythms. However, evidence is unclear. This cross-sectional study aimed to investigate the relation between nightly fasting duration, meal timing and frequency and metabolic syndrome (MetS) among Iranian adults. Eight hundred fifty adults were recruited in this study. Dietary data were collected by 24-h dietary recalls. Time-related eating patterns were determined as nightly fasting duration, occasions of eating, time and energy proportion of first and last meal and meal frequency on a day. The MetS was recognised on the basis of the National Cholesterol Education Program Adult Treatment Panel III criteria. A binary logistic regression was applied to examine the relation between meal timing and MetS. A significant inverse relation between habitual nightly fasting duration with MetS (OR = 0·74, 95 % CI 0·55, 0·99, P = 0·04) and ‘increased TAG’ (OR = 0·73, 95 % CI 0·55, 0·98, P = 0·03) was found after confounder adjustment. Also, habitual first and last meal energy had no significant connection with MetS. However, the odds of ‘increased fasting blood glucose’ were lower in subjects who consumed ≥25% of habitual energy intake in the last meal (OR = 0·60, 95 % CI 0·42, 0·85, P = 0·005). Having longer nightly fasting duration may be useful for decreasing the risk of both MetS and ‘elevated TAG’. These findings introduce a new insight that time-related eating patterns, instead of nightly fasting duration alone, might be related to cardiometabolic risks in Iranian adults.

Many parasites spend part of their life cycle as infectious forms released from an infected host in the external environment, where they may encounter and infect new hosts. The emergence of infectious life stages often occurs once a day to minimize mortality in adverse environments. In bird hosts, intestinal parasites such as coccidia are generally released with feces in the late afternoon. This dynamic is adaptive since it allows avoiding desiccation and ultraviolet (UV) radiation, thus reducing mortality of oocysts in the environment until transmission to the next host. If this circadian rhythm is the result of natural selection to increase oocyst survival, we may hypothesize that oocysts will appear in feces at different times depending on the environment where hosts live. Particularly, in an environment where UV radiation and desiccation are very low, we may expect oocyst circadian release to disappear since the main selective pressure would be relaxed. We sampled different species of birds in tropical and temperate forests in spring and investigated coccidian oocyst output. A strong circadian variation in the prevalence of hosts shedding coccidian oocyst was detected for species caught in the temperate forest with an increase in prevalence in the late afternoon, whereas prevalence of birds shedding oocysts was constant over the course of the day for most species sampled in the tropical rain forest. These results are consistent with the hypothesis that oocysts’ circadian output is maintained by natural selection to increase oocyst survival. We discuss the adaptive significance of diurnal periodicity in parasite output.

Seasonal affective disorder (SAD) is a recurrent form of major depression, particularly occurring in the winter months with a generally spontaneous remission in spring/summer. The predictable nature of this condition provides a potentially unique opportunity to prevent recurrence in sufferers of SAD. The Cochrane Review discussed here examines the evidence for melatonin and agomelatine in preventing SAD, putting its findings into their clinical context.

The objective of this study was to provide a reliable instrument to measure morningness for upcoming studies in French samples, using the Composite Scale of Morningness (CSM), which has been translated into French. Nursing students (n = 356) completed the questionnaire between February and March 1997. The total score obtained was independent of age and gender, and normally distributed. The reliability was high (Cronbach's α = 0.85), and factorial analysis confirmed the unidimensionality of the scale. Evening-type subjects are thought to score under 31, and morning-type subjects are thought to score above 44. As an external validation, morningness was associated, on weekdays and weekends, with early rising times and bedtimes and early peak times of physical and mental performance. In conclusion, we found that the English and the French versions of the Composite Scale of Morningness gave identical results. The scale is reliable and can be used for French-speaking adult samples. Nevertheless, normative data and other external validity criteria are needed.

We studied circadian thyrotropin (TSH) and prolactin (PRL) response to synthetic thyrotropin-releasing-hormone (protirelin) infusion (200μg IV) at 8 am and 11 pm in 35 drug-free inpatients with DSM III-R Major Depressive Episode and in 22 hospitalized controls. In each group, maximum TSH and PRL responses were lower at 8 am than at 11 pm. The difference between 11 pm-ΔTSH and 8 am-ΔJTSH (ΔΔTSH) was significantly lower in depressed patients compared to controls. No such blunting was observed in PRL responses to protirelin in depressed patients. In the overall population, TSH response to protirelin (ie8 am-ΔTSH, 11 pm-ΔTSH, ΔΔTSH) correlated significantly with TSH circadian parameters (ie mesor and amplitude). These correlations were also observed with PRL (except for ΔΔPRL). TSH mesor and amplitude were lower in depressives than in controls. In contrast, PRL mesor and amplitude were not significantly different between diagnostic groups. ΔΔTSH is thus a chronobiological refinement to the measure of thyroid axis dysfunction in major depression. The blunted TSH response to protirelin suggests that the TRH receptors of the pituitary thyrotrophs are hyposensitive in major depression.

The aim of this study was to investigate for the effects of valpromide on heart rate circadian rhythm in remitted recurrent unipolar and bipolar disorders (DSM-III-R). It consisted of a comparative, randomized, double-blind, repeated cross-over study of valpromide versus placebo over four four-week periods. The primary evaluation criteria was heart rate (HR). Secondary criteria comprised motor activity (MA) and the Bech and Rafaelsen mania assessment scale, Horne and Ostberg questionnaire, Montgomery and Asberg depression rating scale, Spiegel questionnaire, a sleep diary, and Clinical Global Impression. Fifteen patients were included, giving 60 one-month periods (30 valpromide periods and 30 placebo periods).

Cosinor analysis of HR and MA data revealed a difference in amplitude (P = 0.037, analysis of variance, one-tailed test).

The clinical sleep study shows that the duration of sleep was greater with valpromide than with placebo (P = 0.007, one-tailed test). Similarly, evaluation of the quality of sleep by patients themselves showed valpromide to be superior to placebo (P = 0.045, one-tailed test). The results of analysis of the Spiegel questionnaire also confirm the superiority of valpromide over placebo. Safety and compliance were comparable for the active drug and the placebo.

In conclusion, the relatively small sample size requires cautious interpretation of this study. Nevertheless, these initial results show a definite effect of valpromide on a biological rhythm that leads one to suppose that it may be effective through a ‘synchronizing’ effect.