Overfeeding polyunsaturated fat compared to saturated fat does not differentially influence lean tissue accumulation in overweight individuals: a randomized controlled trial

BACKGROUND

Fatty acids may influence lean tissue volume and skeletal muscle function. We previously reported in young lean participants that overfeeding polyunsaturated fat (PUFA) compared with saturated fat (SFA) induced greater lean tissue accumulation despite similar weight gain.

OBJECTIVE

In a double-blind randomized controlled trial (RCT), we aimed to investigate if the differential effects of overfeeding SFA and PUFA on lean tissue accumulation could be replicated in individuals with overweight, and identify potential determinants. Further, using substitution models, we investigated associations between SFA and PUFA levels with lean tissue volume, in a large population-based sample (UK Biobank).

METHODS

Sixty-one males and females with overweight (BMI 27.3 (interquartile range 25.4 to 29.3), age 43 (interquartile range 36 to 48)) were overfed SFA (palm oil) or n-6 PUFA (sunflower oil) for 8 weeks. Lean tissue was assessed by magnetic resonance imaging (MRI). We had access to n=13849 participants with data on diet, covariates and MRI measurements of lean tissue, as well as 9119 participants with data on circulating fatty acids, in the UK Biobank.

RESULTS

Body weight gain (mean±SD) was similar in PUFA (2.01±1.90 kg) and SFA (2.31±1.38 kg) groups. Lean tissue increased to a similar extent (0.54±0.93 L and 0.67±1.21 L for PUFA and SFA group, respectively, with a difference between groups of 0.07 (-0,21, 0,35)). We observed no differential effects on circulating amino acids, myostatin or interleukin-15 and no clear determinants of lean tissue accumulation. Similar non-significant results for SFA and PUFA were observed in UK Biobank, but circulating fatty acids demonstrated ambiguous and sex-dependent associations.

CONCLUSION

Overfeeding SFA or PUFA does not differentially affect lean tissue accumulation during 8 weeks in individuals with overweight. A lack of dietary fat type-specific effects on lean tissue is supported by specified substitution models in a large population-based cohort consuming their habitual diet.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02211612.

Habitual Short Sleep Duration, Diet, and Development of Type 2 Diabetes in Adults

Importance

Understanding the interplay between sleep duration, dietary habits, and the risk of developing type 2 diabetes (T2D) is crucial for public health and diabetes prevention strategies.

Objective

To investigate the associations of type of diet and duration of sleep with the development of T2D.

Design, Setting, and Participants

Data derived from the UK Biobank baseline investigation (2006-2010) were analyzed for this cohort study between May 1 and September 30, 2023. The association between sleep duration and healthy dietary patterns with the risk of T2D was investigated during a median (IQR) follow-up of 12.5 (11.8-13.2) years (end of follow-up, September 30, 2021).

Exposure

For the analysis, 247 867 participants were categorized into 4 sleep duration groups: normal (7-8 hours per day), mild short (6 hours per day), moderate short (5 hours per day), and extreme short (3-4 hours per day). Their dietary habits were evaluated based on population-specific consumption of red meat, processed meat, fruits, vegetables, and fish, resulting in a healthy diet score ranging from 0 (unhealthiest) to 5 (healthiest).

Main Outcomes and Measures

Cox proportional hazards regression analysis was used to calculate hazard ratios (HRs) and 95% CIs for the development of T2D across various sleep duration groups and healthy diet scores.

Results

The cohort comprised 247 867 participants with a mean [SD] age of 55.9 [8.1] years, of whom 52.3% were female. During the follow-up, 3.2% of participants were diagnosed with T2D based on hospital registry data. Cox regression analysis, adjusted for confounding variables, indicated a significant increase in the risk of T2D among participants with 5 hours or less of daily sleep. Individuals sleeping 5 hours per day exhibited a 1.16 adjusted HR (95% CI, 1.05-1.28), and individuals sleeping 3 to 4 hours per day exhibited a 1.41 adjusted HR (95% CI, 1.19-1.68) compared with individuals with normal sleep duration. Furthermore, individuals with the healthiest dietary patterns had a reduced risk of T2D (HR, 0.75 [95% CI, 0.63-0.88]). The association between short sleep duration and increased risk of T2D persisted even for individuals following a healthy diet, but there was no multiplicative interaction between sleep duration and healthy diet score.

Conclusions and Relevance

In this cohort study involving UK residents, habitual short sleep duration was associated with increased risk of developing T2D. This association persisted even among participants who maintained a healthy diet. To validate these findings, further longitudinal studies are needed, incorporating repeated measures of sleep (including objective assessments) and dietary habits.

OSA Is Associated With the Human Gut Microbiota Composition and Functional Potential in the Population-Based Swedish CardioPulmonary bioImage Study

BACKGROUND

OSA is a common sleep-breathing disorder linked to increased risk of cardiovascular disease. Intermittent upper airway obstruction and hypoxia, hallmarks of OSA, have been shown in animal models to induce substantial changes to the gut microbiota composition, and subsequent transplantation of fecal matter to other animals induced changes in BP and glucose metabolism.

RESEARCH QUESTION

Does OSA in adults associate with the composition and functional potential of the human gut microbiota?

STUDY DESIGN AND METHODS

We used respiratory polygraphy data from up to 3,570 individuals 50 to 64 years of age from the population-based Swedish Cardiopulmonary bioimage Study combined with deep shotgun metagenomics of fecal samples to identify cross-sectional associations between three OSA parameters covering apneas and hypopneas, cumulative sleep time in hypoxia, and number of oxygen desaturation events with gut microbiota composition. Data collection about potential confounders was based on questionnaires, onsite anthropometric measurements, plasma metabolomics, and linkage with the Swedish Prescribed Drug Register.

RESULTS

We found that all three OSA parameters were associated with lower diversity of species in the gut. Furthermore, in multivariable-adjusted analysis, the OSA-related hypoxia parameters were associated with the relative abundance of 128 gut bacterial species, including higher abundance of Blautia obeum and Collinsella aerofaciens. The latter species was also independently associated with increased systolic BP. Furthermore, the cumulative time in hypoxia during sleep was associated with the abundance of genes involved in nine gut microbiota metabolic pathways, including propionate production from lactate. Finally, we observed two heterogeneous sets of plasma metabolites with opposite association with species positively and negatively associated with hypoxia parameters, respectively.

INTERPRETATION

OSA-related hypoxia, but not the number of apneas/hypopneas, is associated with specific gut microbiota species and functions. Our findings lay the foundation for future research on the gut microbiota-mediated health effects of OSA.

Exposure to a more unhealthy diet impacts sleep microstructure during normal sleep and recovery sleep: A randomized trial

OBJECTIVE

Although intake of specific macronutrients has been associated with sleep parameters, interventional evidence is lacking. Therefore, this randomized trial was conducted to examine how a more unhealthy high-fat/high-sugar (HFHS) diet impacts sleep in humans.

METHODS

In a crossover study, 15 healthy young men consumed two isocaloric diets in random order for a week: an HFHS and a low-fat/low-sugar diet. Following each diet, in-lab sleep was recorded using polysomnography during a full night of sleep and during recovery sleep after extended wakefulness. Sleep duration, macrostructure, and microstructure (oscillatory pattern and slow waves) were investigated using machine learning-based algorithms.

RESULTS

Sleep duration did not differ across the diets based on actigraphy and the in-lab polysomnography. Sleep macrostructure was similar after 1 week on each diet. Compared with the low-fat/low-sugar diet, consumption of the HFHS diet resulted in reduced delta power, delta to beta ratio, and slow wave amplitude but increased alpha and theta power during deep sleep. During recovery sleep, similar sleep oscillatory changes were observed.

CONCLUSIONS

Short-term consumption of a more unhealthy diet alters sleep oscillatory features that regulate the restorative properties of sleep. Whether such changes can mediate adverse health outcomes associated with consumption of an unhealthier diet warrants investigation.

A weighted blanket increases pre-sleep salivary concentrations of melatonin in young, healthy adults

Weighted blankets have emerged as a potential non-pharmacological intervention to ease conditions such as insomnia and anxiety. Despite a lack of experimental evidence, these alleged effects are frequently attributed to a reduced activity of the endogenous stress systems and an increased release of hormones such as oxytocin and melatonin. Thus, the aim of the present in-laboratory crossover study (26 young and healthy participants, including 15 men and 11 women) was to investigate if using a weighted blanket (~12% of body weight) at bedtime resulted in higher salivary concentrations of melatonin and oxytocin compared with a light blanket (~2.4% of body weight). We also examined possible differences in salivary concentrations of the stress hormone cortisol, salivary alpha-amylase activity (as an indicative metric of sympathetic nervous system activity), subjective sleepiness, and sleep duration. When using a weighted blanket, the 1 hour increase of salivary melatonin from baseline (i.e., 22:00) to lights off (i.e., 23:00) was about 32% higher (p = 0.011). No other significant differences were found between the blanket conditions, including subjective sleepiness and total sleep duration. Our study is the first to suggest that using a weighted blanket may result in a more significant release of melatonin at bedtime. Future studies should investigate whether the stimulatory effect on melatonin secretion is observed on a nightly basis when frequently using a weighted blanket over weeks to months. It remains to be determined whether the observed increase in melatonin may be therapeutically relevant for the previously described effects of the weighted blanket on insomnia and anxiety.

Gastric bypass alters diurnal feeding behavior and reprograms the hepatic clock to regulate endogenous glucose flux

The molecular clock machinery regulates several homeostatic rhythms, including glucose metabolism. We previously demonstrated that Roux-en-Y gastric bypass (RYGB) has a weight-independent effect on glucose homeostasis and transiently reduces food intake. In this study we investigate the effects of RYGB on diurnal eating behavior as well as on the molecular clock and this clock's requirement for the metabolic effects of this bariatric procedure in obese mice. We find that RYGB reversed the high-fat diet-induced disruption in diurnal eating pattern during the early postsurgery phase of food reduction. Dark-cycle pair-feeding experiments improved glucose tolerance to the level of bypass-operated animals during the physiologic fasting phase (Zeitgeber time 2, ZT2) but not the feeding phase (ZT14). Using a clock gene reporter mouse model (mPer2Luc), we reveal that RYGB induced a liver-specific phase shift in peripheral clock oscillation with no changes to the central clock activity within the suprachiasmatic nucleus. In addition, we show that weight loss effects were attenuated in obese ClockΔ19 mutant mice after RYGB that also failed to improve glucose metabolism after surgery, specifically hepatic glucose production. We conclude that RYGB reprograms the peripheral clock within the liver early after surgery to alter diurnal eating behavior and regulate hepatic glucose flux.

Time-restricted feeding mitigates obesity through adipocyte thermogenesis

Misalignment of feeding rhythms with the light-dark cycle leads to disrupted peripheral circadian clocks and obesity. Conversely, restricting feeding to the active period mitigates metabolic syndrome through mechanisms that remain unknown. We found that genetic enhancement of adipocyte thermogenesis through ablation of the zinc finger protein 423 (ZFP423) attenuated obesity caused by consumption of a high-fat diet during the inactive (light) period by increasing futile creatine cycling in mice. Circadian control of adipocyte creatine metabolism underlies the timing of diet-induced thermogenesis, and enhancement of adipocyte circadian rhythms through overexpression of the clock activator brain and muscle Arnt-like protein-1 (BMAL1) ameliorated metabolic complications during diet-induced obesity. These findings uncover rhythmic creatine-mediated thermogenesis as an essential mechanism that drives metabolic benefits during time-restricted feeding.

Association of Daily Eating Duration and Day-To-Day Variability in the Timing of Eating With Fatal Cancer Risk in Older Men

Meal timing has significant effects on health. However, whether meal timing is associated with the risk of developing and dying of cancer is not well-researched in humans. In the present study, we used data from 941 community-dwelling men aged 71 years who participated in the Uppsala Longitudinal Study of Adult Men to examine the association of meal timing with cancer morbidity and fatal cancer. The following meal timing variables were derived from 7-day food diaries: (i) daily eating duration, i.e., the time between the first and last eating episode of an arbitrary day; (ii) the calorically weighted midpoint of the daily eating interval, a proxy of when the eating window typically occurs during an arbitrary day; and (iii) the day-to-day variability in the timing of eating. We also assessed the reported daily energy intake reliability using the Goldberg method. During a mean observational period of 13.4 years, 277 men (29.4%) were diagnosed with cancer. Furthermore, 191 men (20%) died from cancer during 14.7 years of follow-up. As shown by Cox regression adjusted for potential confounders (e.g., smoking status and daily energy intake), men with reliable dietary reports whose daily eating intervals were on average 13 h long had a 2.3-fold greater fatal cancer risk than men whose daily eating windows were on average about 11 h long. We also found that men with an average day-to-day variability in the timing of eating of 48 to 74 min had a 2- to 2.2-fold higher fatal cancer risk than those with the lowest average day-to-day variability in the timing of eating (i.e., 23 min). No clear associations were found in men with inadequate dietary reports, emphasizing the need to consider the reliability of dietary records in nutritional epidemiology. To fully unlock its potential, studies are needed to test whether recommendations to time-restrict the 24-h eating interval and reduce day-to-day variability in the timing of eating can meaningfully alter the risk of death due to cancer.

Effects of curtailed sleep on cardiac stress biomarkers following high-intensity exercise

Objective

Physical exercise—especially at high intensity—is known to impose cardiac stress, as mirrored by, e.g., increased blood levels of cardiac stress biomarkers such as cardiac Troponin T (cTnT) and NT-proBNP. We examined healthy young participants to determine whether a few nights of short sleep duration alter the effects of acute exercise on these blood biomarkers.

Methods

Sixteen men participated in a randomized order in a crossover design, comprising three consecutive nights of a) normal sleep duration (NS, 8.5 h of sleep/night) and b) sleep restriction (SR, 4.25 h of sleep/night). Blood was repeatedly sampled for determination of NT-proBNP and cTnT serum levels before and after a high-intensity exercise protocol (i.e., 75% VO₂^maxReserve cycling on an ergometer).

Results

Under pre-exercise sedentary conditions, blood levels of cTnT and NT-proBNP did not significantly differ between the sleep conditions (P > 0.10). However, in response to exercise, the surge of circulating cTnT was significantly greater following SR than NS (+37–38% at 120–240 min post-exercise, P ≤ 0.05). While blood levels of NT-proBNP rose significantly in response to exercise, they did not differ between the sleep conditions.

Conclusion

Recurrent sleep restriction may increase the cardiac stress response to acute high-intensity exercise in healthy young individuals. However, our findings must be further confirmed in women, older subjects and in patients with a history of heart disease.

•

Chronic sleep curtailment increases the risk of cardiovascular disease.

•

Here, we examined whether exercise-induced cardiac strain in healthy young adults is altered by sleep curtailment.

•

Blood levels of the cardiac stress marker troponin were higher after exercise under conditions of recurrent sleep restriction.

•

Sleep restriction may increase exercise-induced cardiac strain in adults.

Sleep and daytime problems during the COVID-19 pandemic and effects of coronavirus infection, confinement and financial suffering: a multinational survey using a harmonised questionnaire

OBJECTIVES

Sleep is important for human health and well-being. No previous study has assessed whether the COVID-19 pandemic impacts sleep and daytime function across the globe.

METHODS

This large-scale international survey used a harmonised questionnaire. Fourteen countries participated during the period of May-August 2020. Sleep and daytime problems (poor sleep quality, sleep onset and maintenance problems, nightmares, hypnotic use, fatigue and excessive sleepiness) occurring 'before' and 'during' the pandemic were investigated. In total, 25 484 people participated and 22 151 (86.9%) responded to the key parameters and were included. Effects of COVID-19, confinement and financial suffering were considered. In the fully adjusted logistic regression models, results (weighted and stratified by country) were adjusted for gender, age, marital status, educational level, ethnicity, presence of sleep problems before COVID-19 and severity of the COVID-19 pandemic in each country at the time of the survey.

RESULTS

The responders were mostly women (64%) with a mean age 41.8 (SD 15.9) years (median 39, range 18-95). Altogether, 3.0% reported having had COVID-19; 42.2% reported having been in confinement; and 55.9% had suffered financially. All sleep and daytime problems worsened during the pandemic by about 10% or more. Also, some participants reported improvements in sleep and daytime function. For example, sleep quality worsened in about 20% of subjects and improved in about 5%. COVID-19 was particularly associated with poor sleep quality, early morning awakening and daytime sleepiness. Confinement was associated with poor sleep quality, problems falling asleep and decreased use of hypnotics. Financial suffering was associated with all sleep and daytime problems, including nightmares and fatigue, even in the fully adjusted logistic regression models.

CONCLUSIONS

Sleep problems, fatigue and excessive sleepiness increased significantly worldwide during the first phase of the COVID-19 pandemic. Problems were associated with confinement and especially with financial suffering.

NADH inhibition of SIRT1 links energy state to transcription during time-restricted feeding

In mammals, circadian rhythms are entrained to the light cycle and drive daily oscillations in levels of NAD+, a cosubstrate of the class III histone deacetylase sirtuin 1 (SIRT1) that associates with clock transcription factors. Although NAD+ also participates in redox reactions, the extent to which NAD(H) couples nutrient state with circadian transcriptional cycles remains unknown. Here we show that nocturnal animals subjected to time-restricted feeding of a calorie-restricted diet (TRF-CR) only during night-time display reduced body temperature and elevated hepatic NADH during daytime. Genetic uncoupling of nutrient state from NADH redox state through transduction of the water-forming NADH oxidase from Lactobacillus brevis (LbNOX) increases daytime body temperature and blood and liver acyl-carnitines. LbNOX expression in TRF-CR mice induces oxidative gene networks controlled by brain and muscle Arnt-like protein 1 (BMAL1) and peroxisome proliferator-activated receptor alpha (PPARα) and suppresses amino acid catabolic pathways. Enzymatic analyses reveal that NADH inhibits SIRT1 in vitro, corresponding with reduced deacetylation of SIRT1 substrates during TRF-CR in vivo. Remarkably, Sirt1 liver nullizygous animals subjected to TRF-CR display persistent hypothermia even when NADH is oxidized by LbNOX. Our findings reveal that the hepatic NADH cycle links nutrient state to whole-body energetics through the rhythmic regulation of SIRT1.

Sleep and circadian rhythms: pillars of health-a Keystone Symposia report

The human circadian system consists of the master clock in the suprachiasmatic nuclei of the hypothalamus as well as in peripheral molecular clocks located in organs throughout the body. This system plays a major role in the temporal organization of biological and physiological processes, such as body temperature, blood pressure, hormone secretion, gene expression, and immune functions, which all manifest consistent diurnal patterns. Many facets of modern life, such as work schedules, travel, and social activities, can lead to sleep/wake and eating schedules that are misaligned relative to the biological clock. This misalignment can disrupt and impair physiological and psychological parameters that may ultimately put people at higher risk for chronic diseases like cancer, cardiovascular disease, and other metabolic disorders. Understanding the mechanisms that regulate sleep circadian rhythms may ultimately lead to insights on behavioral interventions that can lower the risk of these diseases. On February 25, 2021, experts in sleep, circadian rhythms, and chronobiology met virtually for the Keystone eSymposium "Sleep & Circadian Rhythms: Pillars of Health" to discuss the latest research for understanding the bidirectional relationships between sleep, circadian rhythms, and health and disease.

Acute sleep loss alters circulating fibroblast growth factor 21 levels in humans: A randomised crossover trial

The hormone fibroblast growth factor 21 (FGF21) modulates tissue metabolism and circulates at higher levels in metabolic conditions associated with chronic sleep-wake disruption, such as type 2 diabetes and obesity. In the present study, we investigated whether acute sleep loss impacts circulating levels of FGF21 and tissue-specific production, and response pathways linked to FGF21. A total of 15 healthy normal-weight young men participated in a randomised crossover study with two conditions, sleep loss versus an 8.5-hr sleep window. The evening before each intervention, fasting blood was collected. Fasting, post-intervention morning skeletal muscle and adipose tissue samples underwent quantitative polymerase chain reaction and DNA methylation analyses, and serum FGF21 levels were measured before and after an oral glucose tolerance test. Serum levels of FGF21 were higher after sleep loss compared with sleep, both under fasting conditions and following glucose intake (~27%-30%, p = 0.023). Fasting circulating levels of fibroblast activation protein, a protein which can degrade circulating FGF21, were not altered by sleep loss, whereas DNA methylation in the FGF21 promoter region increased only in adipose tissue. However, even though specifically the muscle exhibited transcriptional changes indicating adverse alterations to redox and metabolic homeostasis, no tissue-based changes were observed in expression of FGF21, its receptors, or selected signalling targets, in response to sleep loss. In summary, we found that acute sleep loss resulted in increased circulating levels of FGF21 in healthy young men, which may occur independent of a tissue-based stress response in metabolic peripheral tissues. Further studies may decipher whether changes in FGF21 signalling after sleep loss modulate metabolic outcomes associated with sleep or circadian disruption.

You are when you eat: on circadian timing and energy balance

The neuronal mechanisms that establish 24-hour rhythms in feeding and metabolism remain incompletely understood. In this issue of the JCI, Adlanmerini and colleagues explored the relationship between temporal and homeostatic control of energy balance by focusing on mice that lacked the genes encoding the clock repressor elements REV-ERBα and -β, specifically in the tuberal hypothalamus. Notably, the clock transcription cycle mediated intraneuronal response to the adipostatic hormone leptin. These results show that REV-ERBα and -β in the hypothalamus are necessary for maintaining leptin responsiveness and metabolic homeostasis and lay the foundation to explore how transcriptional changes may link energy-sensing cell types with day/night rhythms. Such information may lead to therapeutics that alleviate the adverse effects of chronic shift work.

Evening-types show highest increase of sleep and mental health problems during the COVID-19 pandemic - Multinational study on 19,267 adults

Study Objectives

Individual circadian type is a ubiquitous trait defining sleep, with eveningness often associated with poorer sleep and mental health than morningness. However, it is unknown whether COVID-19 pandemic has differentially affected sleep and mental health depending on the circadian type. Here, the differences in sleep and mental health between circadian types are examined globally before and during the COVID-19 pandemic.

Methods

The sample collected between May and August 2020 across 12 countries/regions consisted of 19 267 adults with information on their circadian type. Statistical analyses were performed by using Complex Sample procedures, stratified by country and weighted by the number of inhabitants in the country/area of interest and by the relative number of responders in that country/area.

Results

Evening-types had poorer mental health, well-being, and quality of life or health than other circadian types during the pandemic. Sleep–wake schedules were delayed especially on working days, and evening-types reported an increase in sleep duration. Sleep problems increased in all circadian types, but especially among evening-types, moderated by financial suffering and confinement. Intermediate-types were less vulnerable to sleep changes, although morningness protected from most sleep problems. These findings were confirmed after adjusting for age, sex, duration of the confinement, or socio-economic status during the pandemic.

Conclusions

These findings indicate an alarming increase in sleep and mental health problems, especially among evening-types as compared to other circadian types during the pandemic.

The association between high risk of sleep apnea, comorbidities, and risk of COVID-19: a population-based international harmonized study

PURPOSE

Obstructive sleep apnea (OSA) may increase the risk of severe COVID-19; however, the level of potential modulation has not yet been established. The objective of the study was to determine the association between high risk of OSA, comorbidities, and increased risk for COVID-19, hospitalization, and intensive care unit (ICU) treatment.

METHODS

We conducted a cross-sectional population-based web survey in adults in 14 countries/regions. The survey included sociodemographic variables and comorbidities. Participants were asked questions about COVID-19, hospitalization, and ICU treatment. Standardized questionnaire (STOP questionnaire for high risk of OSA) was included. Multivariable logistic regression was conducted adjusting for various factors.

RESULTS

Out of 26,539 respondents, 20,598 (35.4% male) completed the survey. Mean age and BMI of participants were 41.5 ± 16.0 years and 24.0 ± 5.0 kg/m², respectively. The prevalence of physician-diagnosed OSA was 4.1% and high risk of OSA was 9.5%. We found that high risk of OSA (adjusted odds ratio (aOR) 1.72, 95% confidence interval (CI): 1.20, 2.47) and diabetes (aOR 2.07, 95% CI: 1.23, 3.48) were associated with reporting of a COVID-19 diagnosis. High risk for OSA (aOR 2.11, 95% CI: 1.10-4.01), being male (aOR: 2.82, 95% CI: 1.55-5.12), having diabetes (aOR: 3.93, 95% CI: 1.70-9.12), and having depression (aOR: 2.33, 95% CI: 1.15-4.77) were associated with increased risk of hospitalization or ICU treatment.

CONCLUSIONS

Participants at high risk of OSA had increased odds of having COVID-19 and were two times more likely to be hospitalized or treated in ICU.

Social Jetlag Changes During the COVID-19 Pandemic as a Predictor of Insomnia - A Multi-National Survey Study

PURPOSE

Lifestyle and work habits have been drastically altered by restrictions due to the COVID-19 pandemic. Whether the associated changes in sleep timing modulate the risk of suffering from symptoms of insomnia, the most prevalent sleep disorder, is however incompletely understood. Here, we evaluate the association between the early pandemic-associated change in 1) the magnitude of social jetlag (SJL) - ie, the difference between sleep timing on working vs free days - and 2) symptoms of insomnia.

PATIENTS AND METHODS

A total of 14,968 anonymous participants (mean age: 40 years; 64% females) responded to a standardized internet-based survey distributed across 14 countries. Using logistic multivariate regression, we examined the association between the degree of social jetlag and symptoms of insomnia, controlling for important confounders like social restriction extension, country specific COVID-19 severity and psychological distress, for example.

RESULTS

In response to the pandemic, participants reported later sleep timing, especially during workdays. Most participants (46%) exhibited a reduction in their SJL, whereas 20% increased it; and 34% reported no change in SJL. Notably, we found that both increased and decreased SJL, as a result of the COVID-19 pandemic, were associated with later sleep midpoint (indicating a later chronotype) as well as more recurrent and moderate-to-severe symptoms of insomnia (about 23-54% higher odds ratio than subjects with unchanged SJL). Primarily those with reduced SJL shifted their bedtimes to a later timepoint, compared with those without changes in SJL.

CONCLUSION

Our findings offer important insights into how self-reported changes to the stability of sleep/wake timing, as reflected by changes in SJL, can be a critical marker of the risk of experiencing insomnia-related symptoms - even when individuals manage to reduce their social jetlag. These findings emphasize the clinical importance of analyzing sleep-wake regularity.

Abdominal Fat and Metabolic Health Markers but Not PNPLA3 Genotype Predicts Liver Fat Accumulation in Response to Excess Intake of Energy and Saturated Fat in Healthy Individuals

Background: Saturated fat (SFA) has consistently been shown to increase liver fat, but the response appears variable at the individual level. Phenotypic and genotypic characteristics have been demonstrated to modify the hypercholesterolemic effect of SFA but it is unclear which characteristics that predict liver fat accumulation in response to a hypercaloric diet high in SFA.

Objective: To identify predictors of liver fat accumulation in response to an increased intake of SFA.

Design: We pooled our two previously conducted double-blind randomized trials (LIPOGAIN and LIPOGAIN-2, clinicaltrials.gov NCT01427140 and NCT02211612) and used data from the n = 49 metabolically healthy men (n = 32) and women (n = 17) randomized to a hypercaloric diet through addition of SFA-rich muffins for 7–8 weeks. Associations between clinical and metabolic variables at baseline and changes in liver fat during the intervention were analyzed using Spearman rank correlation. Linear regression was used to generate a prediction model.

Results: Liver fat increased by 33% (IQR 5.4–82.7%; P < 0.0001) in response to excess energy intake and this was not associated (r = 0.17, P = 0.23) with the increase in body weight (1.9 kg; IQR 1.1–2.9 kg). Liver fat accumulation was similar (P = 0.28) in carriers (33%, IQR 14–79%) and non-carriers (33%, IQR −11 to +87%) of the PNPLA3-I148M variant. Baseline visceral and liver fat content, as well as levels of the liver enzyme γ-glutamyl transferase (GT), were the strongest positive predictors of liver fat accumulation—in contrast, adiponectin and the fatty acid 17:0 in adipose tissue were the only negative predictors in univariate analyses. A regression model based on eight clinical and metabolic variables could explain 81% of the variation in liver fat accumulation.

Conclusion: Our results suggest there exists a highly inter-individual variation in the accumulation of liver fat in metabolically healthy men and women, in response to an increased energy intake from SFA and carbohydrates that occurs over circa 2 months. This marked variability in liver fat accumulation could largely be predicted by a set of clinical (e.g., GT and BMI) and metabolic (e.g., fatty acids, HOMA-IR, and adiponectin) variables assessed at baseline.

The role of exercise-induced peripheral factors in sleep regulation

BACKGROUND

Recurrently disrupted sleep is a widespread phenomenon in our society. This is worrisome as chronically impaired sleep increases the risk of numerous diseases that place a heavy burden on health services worldwide, including type 2 diabetes, obesity, depression, cardiovascular disease, and dementia. Therefore, strategies mitigating the current societal sleep crisis are needed.

SCOPE OF REVIEW

Observational and interventional studies have found that regular moderate to intensive exercise is associated with better subjective and objective sleep in humans, with and without pre-existing sleep disturbances. Here, we summarize recent findings from clinical studies in humans and animal experiments suggesting that molecules that are expressed, produced, and released by the skeletal muscle in response to exercise may contribute to the sleep-improving effects of exercise.

MAJOR CONCLUSIONS

Exercise-induced skeletal muscle recruitment increases blood concentrations of signaling molecules, such as the myokine brain-derived neurotrophic factor (BDNF), which has been shown to increase the depth of sleep in animals. As reviewed herein, BDNF and other muscle-induced factors are likely to contribute to the sleep-promoting effects of exercise. Despite progress in the field, however, several fundamental questions remain. For example, one central question concerns the optimal time window for exercise to promote sleep. It is also unknown whether the production of muscle-induced peripheral factors promoting sleep is altered by acute and chronic sleep disturbances, which has become increasingly common in the modern 24/7 lifestyle.

An epigenetic clock for human skeletal muscle

BACKGROUND

Ageing is associated with DNA methylation changes in all human tissues, and epigenetic markers can estimate chronological age based on DNA methylation patterns across tissues. However, the construction of the original pan-tissue epigenetic clock did not include skeletal muscle samples and hence exhibited a strong deviation between DNA methylation and chronological age in this tissue.

METHODS

To address this, we developed a more accurate, muscle-specific epigenetic clock based on the genome-wide DNA methylation data of 682 skeletal muscle samples from 12 independent datasets (18-89 years old, 22% women, 99% Caucasian), all generated with Illumina HumanMethylation (HM) arrays (HM27, HM450, or HMEPIC). We also took advantage of the large number of samples to conduct an epigenome-wide association study of age-associated DNA methylation patterns in skeletal muscle.

RESULTS

The newly developed clock uses 200 cytosine-phosphate-guanine dinucleotides to estimate chronological age in skeletal muscle, 16 of which are in common with the 353 cytosine-phosphate-guanine dinucleotides of the pan-tissue clock. The muscle clock outperformed the pan-tissue clock, with a median error of only 4.6 years across datasets (vs. 13.1 years for the pan-tissue clock, P < 0.0001) and an average correlation of ρ = 0.62 between actual and predicted age across datasets (vs. ρ = 0.51 for the pan-tissue clock). Lastly, we identified 180 differentially methylated regions with age in skeletal muscle at a false discovery rate < 0.005. However, gene set enrichment analysis did not reveal any enrichment for gene ontologies.

CONCLUSIONS

We have developed a muscle-specific epigenetic clock that predicts age with better accuracy than the pan-tissue clock. We implemented the muscle clock in an r package called Muscle Epigenetic Age Test available on Bioconductor to estimate epigenetic age in skeletal muscle samples. This clock may prove valuable in assessing the impact of environmental factors, such as exercise and diet, on muscle-specific biological ageing processes.

0317 Impact of Recurrent Partial Sleep Loss Combined with Acute Exercise on Circulating and Adipose Tissue Levels of Leptin, Adiponectin and Ghrelin in Healthy Young Individuals

Introduction

Chronic sleep loss and aerobic exercise have opposing effects on body weight maintenance. The effects of sleep loss on circulating levels of the orexigenic hormone ghrelin and the anorexigenic hormone leptin have been extensively studied. In contrast, how these changes interact with acute exercise, and whether these changes are reflected at the tissue level, remains poorly understood.

Methods

In a randomized, 2 session, crossover design, 16 normal-weight young men were studied following three nights of partial sleep deprivation (4.25 hr sleep opportunity each night) and three nights of normal sleep (8.5-h sleep opportunity), monitored in a sleep laboratory. Each condition was followed by 30 min of intense morning ergometer cycling. Plasma levels of leptin and ghrelin, as well adipose tissue mRNA levels of leptin and adiponectin, were measured before and after each exercise intervention.

Results

In response to acute exercise, circulating levels of both leptin (ANOVA time effect: P&lt;0.001) and ghrelin (time: P&lt;0.001) decreased immediately (+15 min), and remained significantly lower +30, +60 and +240 min post exercise for leptin (all P&lt;0.05), and up until +30 min post exercise for ghrelin. These effects were seen regardless of sleep condition (ANOVA sleep condition: P&gt;0.10). In adipose tissue, mRNA expression of leptin and adiponectin was not different between the sleep conditions (ANOVA sleep condition: P&gt;0.10). In contrast, mRNA levels of leptin decreased (P=0.017), whereas adiponectin mRNA increased (P=0.010) 3.5 hours post vs. pre exercise. The decrease in leptin in response to exercise appeared to mainly occur following sleep loss (P=0.066) and not after normal sleep (P=0.38).

Conclusion

Our results suggest that both circulating and adipose tissue levels of appetite-regulating hormones are altered in response to acute aerobic exercise, in a manner that does not depend on prior sleep history. Whether these findings apply to older, female, or metabolically ill individuals - and whether they may differ in response to circadian misalignment, or evening exercise - remains to be established.

Support

The Swedish Society for Medical Research, the Swedish Society of Medicine, the Swedish Research Council and the Göran Gustafsson; Swedish Brain; Åke Wiberg and NovoNordisk Foundations.

NAD+ Controls Circadian Reprogramming through PER2 Nuclear Translocation to Counter Aging

Disrupted sleep-wake and molecular circadian rhythms are a feature of aging associated with metabolic disease and reduced levels of NAD⁺, yet whether changes in nucleotide metabolism control circadian behavioral and genomic rhythms remains unknown. Here, we reveal that supplementation with the NAD⁺ precursor nicotinamide riboside (NR) markedly reprograms metabolic and stress-response pathways that decline with aging through inhibition of the clock repressor PER2. NR enhances BMAL1 chromatin binding genome-wide through PER2^K680 deacetylation, which in turn primes PER2 phosphorylation within a domain that controls nuclear transport and stability and that is mutated in human advanced sleep phase syndrome. In old mice, dampened BMAL1 chromatin binding, transcriptional oscillations, mitochondrial respiration rhythms, and late evening activity are restored by NAD⁺ repletion to youthful levels with NR. These results reveal effects of NAD⁺ on metabolism and the circadian system with aging through the spatiotemporal control of the molecular clock.

Effects of acute sleep loss on diurnal plasma dynamics of CNS health biomarkers in young men

Objective

Disrupted sleep increases CSF levels of tau and β-amyloid (Aβ) and is associated with an increased risk of Alzheimer disease (AD). Our aim was to determine whether acute sleep loss alters diurnal profiles of plasma-based AD-associated biomarkers.

Methods

In a 2-condition crossover study, 15 healthy young men participated in 2 standardized sedentary in-laboratory conditions in randomized order: normal sleep vs overnight sleep loss. Plasma levels of total tau (t-tau), Aβ40, Aβ42, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) were assessed using ultrasensitive single molecule array assays or ELISAs, in the fasted state in the evening prior to, and in the morning after, each intervention.

Results

In response to sleep loss (+17.2%), compared with normal sleep (+1.8%), the evening to morning ratio was increased for t-tau (p = 0.035). No changes between the sleep conditions were seen for levels of Aβ40, Aβ42, NfL, or GFAP (all p > 0.10). The AD risk genotype rs4420638 did not significantly interact with sleep loss–related diurnal changes in plasma levels of Aβ40 or Aβ42 (p > 0.10). Plasma levels of Aβ42 (−17.1%) and GFAP (−12.1%) exhibited an evening to morning decrease across conditions (p < 0.05).

Conclusions

Our exploratory study suggests that acute sleep loss results in increased blood levels of t-tau. These changes provide further evidence that sleep loss may have detrimental effects on brain health even in younger individuals. Larger cohorts are warranted to delineate sleep vs circadian mechanisms, implications for long-term recurrent conditions (e.g., in shift workers), as well as interactions with other lifestyle and genetic factors.

Overeating Saturated Fat Promotes Fatty Liver and Ceramides Compared With Polyunsaturated Fat: A Randomized Trial

CONTEXT

Saturated fatty acid (SFA) vs polyunsaturated fatty acid (PUFA) may promote nonalcoholic fatty liver disease by yet unclear mechanisms.

OBJECTIVE

To investigate if overeating SFA- and PUFA-enriched diets lead to differential liver fat accumulation in overweight and obese humans.

DESIGN

Double-blind randomized trial (LIPOGAIN-2). Overfeeding SFA vs PUFA for 8 weeks, followed by 4 weeks of caloric restriction.

SETTING

General community.

PARTICIPANTS

Men and women who are overweight or have obesity (n = 61).

INTERVENTION

Muffins, high in either palm (SFA) or sunflower oil (PUFA), were added to the habitual diet.

MAIN OUTCOME MEASURES

Lean tissue mass (not reported here). Secondary and exploratory outcomes included liver and ectopic fat depots.

RESULTS

By design, body weight gain was similar in SFA (2.31 ± 1.38 kg) and PUFA (2.01 ± 1.90 kg) groups, P = 0.50. SFA markedly induced liver fat content (50% relative increase) along with liver enzymes and atherogenic serum lipids. In contrast, despite similar weight gain, PUFA did not increase liver fat or liver enzymes or cause any adverse effects on blood lipids. SFA had no differential effect on the accumulation of visceral fat, pancreas fat, or total body fat compared with PUFA. SFA consistently increased, whereas PUFA reduced circulating ceramides, changes that were moderately associated with liver fat changes and proposed markers of hepatic lipogenesis. The adverse metabolic effects of SFA were reversed by calorie restriction.

CONCLUSIONS

SFA markedly induces liver fat and serum ceramides, whereas dietary PUFA prevents liver fat accumulation and reduces ceramides and hyperlipidemia during excess energy intake and weight gain in overweight individuals.

Neurogenetic basis for circadian regulation of metabolism by the hypothalamus

Circadian rhythms are driven by a transcription-translation feedback loop that separates anabolic and catabolic processes across the Earth's 24-h light-dark cycle. Central pacemaker neurons that perceive light entrain a distributed clock network and are closely juxtaposed with hypothalamic neurons involved in regulation of sleep/wake and fast/feeding states. Gaps remain in identifying how pacemaker and extrapacemaker neurons communicate with energy-sensing neurons and the distinct role of circuit interactions versus transcriptionally driven cell-autonomous clocks in the timing of organismal bioenergetics. In this review, we discuss the reciprocal relationship through which the central clock drives appetitive behavior and metabolic homeostasis and the pathways through which nutrient state and sleep/wake behavior affect central clock function.

Transcriptional Basis for Rhythmic Control of Hunger and Metabolism within the AgRP Neuron

The alignment of fasting and feeding with the sleep/wake cycle is coordinated by hypothalamic neurons, though the underlying molecular programs remain incompletely understood. Here, we demonstrate that the clock transcription pathway maximizes eating during wakefulness and glucose production during sleep through autonomous circadian regulation of NPY/AgRP neurons. Tandem profiling of whole-cell and ribosome-bound mRNAs in morning and evening under dynamic fasting and fed conditions identified temporal control of activity-dependent gene repertoires in AgRP neurons central to synaptogenesis, bioenergetics, and neurotransmitter and peptidergic signaling. Synaptic and circadian pathways were specific to whole-cell RNA analyses, while bioenergetic pathways were selectively enriched in the ribosome-bound transcriptome. Finally, we demonstrate that the AgRP clock mediates the transcriptional response to leptin. Our results reveal that time-of-day restriction in transcriptional control of energy-sensing neurons underlies the alignment of hunger and food acquisition with the sleep/wake state.

Acute sleep loss results in tissue-specific alterations in genome-wide DNA methylation state and metabolic fuel utilization in humans

Curtailed sleep promotes weight gain and loss of lean mass in humans, although the underlying molecular mechanisms are poorly understood. We investigated the genomic and physiological impact of acute sleep loss in peripheral tissues by obtaining adipose tissue and skeletal muscle after one night of sleep loss and after one full night of sleep. We find that acute sleep loss alters genome-wide DNA methylation in adipose tissue, and unbiased transcriptome-, protein-, and metabolite-level analyses also reveal highly tissue-specific changes that are partially reflected by altered metabolite levels in blood. We observe transcriptomic signatures of inflammation in both tissues following acute sleep loss, but changes involving the circadian clock are evident only in skeletal muscle, and we uncover molecular signatures suggestive of muscle breakdown that contrast with an anabolic adipose tissue signature. Our findings provide insight into how disruption of sleep and circadian rhythms may promote weight gain and sarcopenia.

Downregulation of the Apelinergic Axis Accelerates Aging, whereas Its Systemic Restoration Improves the Mammalian Healthspan

Aging drives the occurrence of numerous diseases, including cardiovascular disease (CVD). Recent studies indicate that blood from young mice reduces age-associated pathologies. However, the "anti-aging" factors in juvenile circulation remain poorly identified. Here, we characterize the role of the apelinergic axis in mammalian aging and identify apelin as an anti-aging factor. The expression of apelin (apln) and its receptor (aplnr) exhibits an age-dependent decline in multiple organs. Reduced apln signaling perturbs organismal homeostasis; mice harboring genetic deficiency of aplnr or apln exhibit enhanced cardiovascular, renal, and reproductive aging. Genetic or pharmacological abrogation of apln signaling also induces cellular senescence mediated, in part, by the activation of senescence-promoting transcription factors. Conversely, restoration of apln in 15-month-old wild-type mice reduces cardiac hypertrophy and exercise-induced hypertensive response. Additionally, apln-restored mice exhibit enhanced vigor and rejuvenated behavioral and circadian phenotypes. Hence, a declining apelinergic axis promotes aging, whereas its restoration extends the murine healthspan.

A single night of sleep loss impairs objective but not subjective working memory performance in a sex-dependent manner

Acute sleep deprivation can lead to judgement errors and thereby increases the risk of accidents, possibly due to an impaired working memory. However, whether the adverse effects of acute sleep loss on working memory are modulated by auditory distraction in women and men are not known. Additionally, it is unknown whether sleep loss alters the way in which men and women perceive their working memory performance. Thus, 24 young adults (12 women using oral contraceptives at the time of investigation) participated in two experimental conditions: nocturnal sleep (scheduled between 22:30 and 06:30 hours) versus one night of total sleep loss. Participants were administered a digital working memory test in which eight‐digit sequences were learned and retrieved in the morning after each condition. Learning of digital sequences was accompanied by either silence or auditory distraction (equal distribution among trials). After sequence retrieval, each trial ended with a question regarding how certain participants were of the correctness of their response, as a self‐estimate of working memory performance. We found that sleep loss impaired objective but not self‐estimated working memory performance in women. In contrast, both measures remained unaffected by sleep loss in men. Auditory distraction impaired working memory performance, without modulation by sleep loss or sex. Being unaware of cognitive limitations when sleep‐deprived, as seen in our study, could lead to undesirable consequences in, for example, an occupational context. Our findings suggest that sleep‐deprived young women are at particular risk for overestimating their working memory performance.

Aiding sleep in type 2 diabetes: therapeutic considerations

Insomnia and obstructive sleep apnoea (OSA) are more prevalent in patients with type 2 diabetes than in the general population. Both insomnia and OSA have been linked to cardiometabolic alterations (eg, hypertension, increased activity of the sympathetic nervous system, and systemic insulin resistance) that can exacerbate the pathophysiology of type 2 diabetes. Improvement of sleep in patients with diabetes could therefore aid the treatment of diabetes. To help health practitioners choose the best clinical tool to improve their patients' sleep without detrimentally affecting glucose regulation, this Review critically analyses the effects of common treatments for insomnia and OSA on both sleep and glucose metabolism in patients with type 2 diabetes. These treatments include pharmaceutical sleep aids (eg, benzodiazepine receptor agonists, melatonin) and cognitive behavioural therapy for insomnia, continuous positive airway pressure for OSA, and lifestyle interventions.

Association between long sleep duration and increased risk of obesity and type 2 diabetes: A review of possible mechanisms

For the last two decades research has revealed an alarming association between short sleep duration and metabolic disorders. In tandem, the hormonal, behavioral, and genetic mechanisms underlying this relationship have been extensively investigated and reviewed. However, emerging evidence is revealing that excessive sleep duration has remarkably similar deleterious effects. Unfortunately, to date there has been little attention to what drives this connection. This narrative review therefore aims to summarize existing epidemiological findings, experimental work, and most importantly putative molecular and behavioral mechanisms connecting excessive sleep duration with both obesity and type 2 diabetes mellitus. It will also address recent findings suggesting a worrisome bidirectional effect such that metabolic disorders create a positive feedback loop which further perpetuates excessive sleep.

Candidate mechanisms underlying the association between sleep-wake disruptions and Alzheimer's disease

During wakefulness, extracellular levels of metabolites in the brain increase. These include amyloid beta (Aβ), which contributes to the pathogenesis of Alzheimer's disease (AD). Counterbalancing their accumulation in the brain, sleep facilitates the removal of these metabolites from the extracellular space by convective flow of the interstitial fluid from the para-arterial to the para-venous space. However, when the sleep-wake cycle is disrupted (characterized by increased brain levels of the wake-promoting neuropeptide orexin and increased neural activity), the central nervous system (CNS) clearance of extracellular metabolites is diminished. Disruptions to the sleep-wake cycle have furthermore been linked to increased neuronal oxidative stress and impaired blood-brain barrier function - conditions that have also been proposed to play a role in the development and progression of AD. Notably, recent human and transgenic animal studies have demonstrated that AD-related pathophysiological processes that occur long before the clinical onset of AD, such as Aβ deposition in the brain, disrupt sleep and circadian rhythms. Collectively, as proposed in this review, these findings suggest the existence of a mechanistic interplay between AD pathogenesis and disrupted sleep-wake cycles, which is able to accelerate the development and progression of this disease.

Circadian Clock Interaction with HIF1α Mediates Oxygenic Metabolism and Anaerobic Glycolysis in Skeletal Muscle

Circadian clocks are encoded by a transcription-translation feedback loop that aligns energetic processes with the solar cycle. We show that genetic disruption of the clock activator BMAL1 in skeletal myotubes and fibroblasts increased levels of the hypoxia-inducible factor 1α (HIF1α) under hypoxic conditions. Bmal1^-/- myotubes displayed reduced anaerobic glycolysis, mitochondrial respiration with glycolytic fuel, and transcription of HIF1α targets Phd3, Vegfa, Mct4, Pk-m, and Ldha, whereas abrogation of the clock repressors CRY1/2 stabilized HIF1α in response to hypoxia. HIF1α bound directly to core clock gene promoters, and, when co-expressed with BMAL1, led to transactivation of PER2-LUC and HRE-LUC reporters. Further, genetic stabilization of HIF1α in Vhl^-/- cells altered circadian transcription. Finally, induction of clock and HIF1α target genes in response to strenuous exercise varied according to the time of day in wild-type mice. Collectively, our results reveal bidirectional interactions between circadian and HIF pathways that influence metabolic adaptation to hypoxia.

Gut microbiota and glucometabolic alterations in response to recurrent partial sleep deprivation in normal-weight young individuals

Objective

Changes to the microbial community in the human gut have been proposed to promote metabolic disturbances that also occur after short periods of sleep loss (including insulin resistance). However, whether sleep loss affects the gut microbiota remains unknown.

Methods

In a randomized within-subject crossover study utilizing a standardized in-lab protocol (with fixed meal times and exercise schedules), we studied nine normal-weight men at two occasions: after two nights of partial sleep deprivation (PSD; sleep opportunity 02:45–07:00 h), and after two nights of normal sleep (NS; sleep opportunity 22:30–07:00 h). Fecal samples were collected within 24 h before, and after two in-lab nights, of either NS or PSD. In addition, participants underwent an oral glucose tolerance test following each sleep intervention.

Results

Microbiota composition analysis (V4 16S rRNA gene sequencing) revealed that after two days of PSD vs. after two days of NS, individuals exhibited an increased Firmicutes:Bacteroidetes ratio, higher abundances of the families Coriobacteriaceae and Erysipelotrichaceae, and lower abundance of Tenericutes (all P < 0.05) – previously all associated with metabolic perturbations in animal or human models. However, no PSD vs. NS effect on beta diversity or on fecal short-chain fatty acid concentrations was found. Fasting and postprandial insulin sensitivity decreased after PSD vs. NS (all P < 0.05).

Discussion

Our findings demonstrate that short-term sleep loss induces subtle effects on human microbiota. To what extent the observed changes to the microbial community contribute to metabolic consequences of sleep loss warrants further investigations in larger and more prolonged sleep studies, to also assess how sleep loss impacts the microbiota in individuals who already are metabolically compromised.

•

Possibly the first results of how short sleep impacts the human gut microbiota.

•

Two nights of short sleep do not significantly impact beta diversity.

•

The Firmicutes to Bacteroidetes ratio is significantly affected by sleep loss.

•

Fecal short-chain fatty acid levels do not change depending on sleep duration.

•

Increased insulin resistance after sleep loss is unrelated to alterations in the microbiota.

Decoding obesity in the brainstem

Neurons in the brainstem are the input for a neural circuit that integrates nutrient signals to control feeding behavior.

Learning and sleep-dependent consolidation of spatial and procedural memories are unaltered in young men under a fixed short sleep schedule

OBJECTIVE

To investigate if a fixed short sleep schedule impairs one of the main functions of sleep, which is to consolidate newly learned memories.

METHODS

Sixteen young men participated in two experimental conditions, each of which lasted for 3 consecutive days and nights in our laboratory: a short sleep schedule (4.25-h sleep opportunity per night) versus a normal sleep schedule (8.5h per night). In the evening after two experimental nights, participants learned locations of 15 card pairs (spatial memory task) and a procedural finger tapping sequence task. Post-sleep retrieval of both memory tasks was tested the next morning.

RESULTS

The short sleep schedule, compared with the normal sleep schedule, considerably altered sleep characteristics, e.g. the proportion of time in slow-wave sleep increased across the three experimental nights. In contrast, neither learning in the evening of day 2, nor subsequent overnight memory consolidation (i.e. concerning the change in memory performance between pre-sleep learning on day 2 and post-sleep retrieval on day 3) differed between the normal and short sleep schedule conditions.

CONCLUSIONS

Our findings suggest that learning in the evening and subsequent sleep-dependent consolidation of procedural and spatial memories are unaltered in young men living under a fixed short sleep schedule. Future studies are warranted to validate our findings in other groups (e.g. adolescents and older subjects) and after more prolonged chronic sleep loss paradigms.

Short Sleep Makes Declarative Memories Vulnerable to Stress in Humans

STUDY OBJECTIVE

This study sought to investigate the role of nocturnal sleep duration for the retrieval of oversleep consolidated memories, both prior to and after being cognitively stressed for ∼30 minutes the next morning.

DESIGN

Participants learned object locations (declarative memory task comprising 15 card pairs) and a finger tapping sequence (procedural memory task comprising 5 digits) in the evening. After learning, participants either had a sleep opportunity of 8 hours (between ∼23:00 and ∼07:00, full sleep condition) or they could sleep between ∼03:00 and ∼07:00 (short sleep condition). Retrieval of both memory tasks was tested in the morning after each sleep condition, both before (∼08:30) and after being stressed (∼09:50).

SETTING

Sleep laboratory.

PARTICIPANTS

15 healthy young men.

RESULTS

The analyses demonstrated that oversleep memory changes did not differ between sleep conditions. However, in their short sleep condition, following stress hallmarked by increased subjective stress feelings, the men were unable to maintain their pre-stress performance on the declarative memory task, whereas their performance on the procedural memory task remained unchanged. While men felt comparably subjectively stressed by the stress intervention, overall no differences between pre- and post-stress recalls were observed following a full night of sleep.

CONCLUSIONS

The findings suggest that 8-h sleep duration, within the range recommended by the US National Sleep Foundation, may not only help consolidate newly learned procedural and declarative memories, but also ensure full access to both during periods of subjective stress.

Acute Sleep Loss Induces Tissue-Specific Epigenetic and Transcriptional Alterations to Circadian Clock Genes in Men

CONTEXT

Shift workers are at increased risk of metabolic morbidities. Clock genes are known to regulate metabolic processes in peripheral tissues, eg, glucose oxidation.

OBJECTIVE

This study aimed to investigate how clock genes are affected at the epigenetic and transcriptional level in peripheral human tissues following acute total sleep deprivation (TSD), mimicking shift work with extended wakefulness.

INTERVENTION

In a randomized, two-period, two-condition, crossover clinical study, 15 healthy men underwent two experimental sessions: x sleep (2230-0700 h) and overnight wakefulness. On the subsequent morning, serum cortisol was measured, followed by skeletal muscle and subcutaneous adipose tissue biopsies for DNA methylation and gene expression analyses of core clock genes (BMAL1, CLOCK, CRY1, PER1). Finally, baseline and 2-h post-oral glucose load plasma glucose concentrations were determined.

MAIN OUTCOME MEASURES

In adipose tissue, acute sleep deprivation vs sleep increased methylation in the promoter of CRY1 (+4%; P = .026) and in two promoter-interacting enhancer regions of PER1 (+15%; P = .036; +9%; P = .026). In skeletal muscle, TSD vs sleep decreased gene expression of BMAL1 (-18%; P = .033) and CRY1 (-22%; P = .047). Concentrations of serum cortisol, which can reset peripheral tissue clocks, were decreased (2449 ± 932 vs 3178 ± 723 nmol/L; P = .039), whereas postprandial plasma glucose concentrations were elevated after TSD (7.77 ± 1.63 vs 6.59 ± 1.32 mmol/L; P = .011).

CONCLUSIONS

Our findings demonstrate that a single night of wakefulness can alter the epigenetic and transcriptional profile of core circadian clock genes in key metabolic tissues. Tissue-specific clock alterations could explain why shift work may disrupt metabolic integrity as observed herein.

Determinants of shortened, disrupted, and mistimed sleep and associated metabolic health consequences in healthy humans

Recent increases in the prevalence of obesity and type 2 diabetes mellitus (T2DM) in modern societies have been paralleled by reductions in the time their denizens spend asleep. Epidemiological studies have shown that disturbed sleep-comprising short, low-quality, and mistimed sleep-increases the risk of metabolic diseases, especially obesity and T2DM. Supporting a causal role of disturbed sleep, experimental animal and human studies have found that sleep loss can impair metabolic control and body weight regulation. Possible mechanisms for the observed changes comprise sleep loss-induced changes in appetite-signaling hormones (e.g., higher levels of the hunger-promoting hormone ghrelin) or hedonic brain responses, altered responses of peripheral tissues to metabolic signals, and changes in energy intake and expenditure. Even though the overall consensus is that sleep loss leads to metabolic perturbations promoting the development of obesity and T2DM, experimental evidence supporting the validity of this view has been inconsistent. This Perspective aims at discussing molecular to behavioral factors through which short, low-quality, and mistimed sleep may threaten metabolic public health. In this context, possible factors that may determine the extent to which poor sleep patterns increase the risk of metabolic pathologies within and across generations will be discussed (e.g., timing and genetics).