Shifts of the hormonal rhythms of melatonin and cortisol after a 4 h bright‐light pulse in different diurnal types

Association of bedtime with the risk of non-alcoholic fatty liver disease among middle-aged and elderly Chinese adults with pre-diabetes and diabetes

BACKGROUND

Emerging evidence indicated that sleep characteristics may play important roles in the development of metabolic disorders. However, little is known as to the association between bedtime and the risk of non-alcoholic fatty liver disease (NAFLD) in individuals with pre-diabetes and diabetes.

METHODS

In a prospective cohort of 10 375 adults aged ≥40 years, 1960 of 3484 eligible pre-diabetic and diabetic individuals were identified for the current study. NAFLD was diagnosed using liver ultrasonography at baseline and at follow-up. Information on bedtime was obtained at baseline using a standard questionnaire.

RESULTS

We documented 433 incident cases of NAFLD among this study population. In multivariable-adjusted logistic regression model, later bedtime was associated with increased risk of NAFLD (29% increased risk per hour of later bedtime). Compared to individuals with bedtime ≤20:00, the odds ratios (95% confidence intervals) of NAFLD for bedtime of 20:00-22:00 and ≥22:00 were 1.56 (1.04-2.34) and 2.05 (1.31-3.20), respectively. In the subgroup analysis, significant associations were observed among those who were overweight or physically inactive, or those with metabolic syndrome or elevated 10-year risks for atherosclerotic cardiovascular disease. When estimating the joint effect of bedtime and other sleep characteristics, higher risk of incident NAFLD was observed in groups of late bed/early rise, late bed/napping (yes), late bed/bad sleeper, or late bed/shorter sleep durations.

CONCLUSIONS

Later bedtime was significantly associated with an increased risk of incident NAFLD in adults with pre-diabetes and diabetes, underscoring the importance of sleep behaviour management in the prevention of NAFLD.

The effect of bright light therapy on depressive symptoms in adults with intellectual disabilities: Results of a multicentre randomized controlled trial

Background

Although a large number of adults with intellectual disabilities have depressive symptoms, non‐pharmacological treatments are scarce. The present authors investigated whether bright light therapy (BLT) is effective in decreasing depressive symptoms compared to care as usual.

Methods

This multicentre randomized controlled trial consisted of three study groups (10,000 lux BLT, dim light BLT and a no‐BLT group). Participants received BLT for 30 min in the morning (14 consecutive days), additional to their regular care. Primary outcome was as follows: depressive symptoms measured with the ADAMS Depressive Mood subscale 1 week after the end of BLT (same time period in the no‐BLT group).

Results

Forty‐one participants were included in our trial. In both BLT groups, a significant decrease in depressive symptoms was seen. No significant differences were found between 10,000 lux BLT and no‐BLT (p = .199) and no significant differences between dim light BLT and no‐BLT (p = .451). A minimum amount of side effects and no adverse events were reported.

Conclusions

In both BLT interventions, a decrease in depressive symptoms was seen. With 10,000 lux BLT, depressive symptoms decreased even below the clinical cut‐off point, which makes BLT a promising intervention for clinical practice.

Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women

IMPORTANCE

Short sleep has been associated with obesity, but to date the association between exposure to artificial light at night (ALAN) while sleeping and obesity is unknown.

OBJECTIVE

To determine whether ALAN exposure while sleeping is associated with the prevalence and risk of obesity.

DESIGN, SETTING, AND PARTICIPANTS

This baseline and prospective analysis included women aged 35 to 74 years enrolled in the Sister Study in all 50 US states and Puerto Rico from July 2003 through March 2009. Follow-up was completed on August 14, 2015. A total of 43 722 women with no history of cancer or cardiovascular disease who were not shift workers, daytime sleepers, or pregnant at baseline were included in the analysis. Data were analyzed from September 1, 2017, through December 31, 2018.

EXPOSURES

Artificial light at night while sleeping reported at enrollment, categorized as no light, small nightlight in the room, light outside the room, and light or television in the room.

MAIN OUTCOMES AND MEASURES

Prevalent obesity at baseline was based on measured general obesity (body mass index [BMI] ≥30.0) and central obesity (waist circumference [WC] ≥88 cm, waist-to-hip ratio [WHR] ≥0.85, or waist-to-height ratio [WHtR]≥0.5). To evaluate incident overweight and obesity, self-reported BMI at enrollment was compared with self-reported BMI at follow-up (mean [SD] follow-up, 5.7 [1.0] years). Generalized log-linear models with robust error variance were used to estimate multivariable-adjusted prevalence ratios (PRs) and relative risks (RRs) with 95% CIs for prevalent and incident obesity.

RESULTS

Among the population of 43 722 women (mean [SD] age, 55.4 [8.9] years), having any ALAN exposure while sleeping was positively associated with a higher prevalence of obesity at baseline, as measured using BMI (PR, 1.03; 95% CI, 1.02-1.03), WC (PR, 1.12; 95% CI, 1.09-1.16), WHR (PR, 1.04; 95% CI, 1.00-1.08), and WHtR (PR, 1.07; 95% CI, 1.04-1.09), after adjusting for confounding factors, with P < .001 for trend for each measure. Having any ALAN exposure while sleeping was also associated with incident obesity (RR, 1.19; 95% CI, 1.06-1.34). Compared with no ALAN, sleeping with a television or a light on in the room was associated with gaining 5 kg or more (RR, 1.17; 95% CI, 1.08-1.27; P < .001 for trend), a BMI increase of 10% or more (RR, 1.13; 95% CI, 1.02-1.26; P = .04 for trend), incident overweight (RR, 1.22; 95% CI,1.06-1.40; P = .03 for trend), and incident obesity (RR, 1.33; 95% CI, 1.13-1.57; P < .001 for trend). Results were supported by sensitivity analyses and additional multivariable analyses including potential mediators such as sleep duration and quality, diet, and physical activity.

CONCLUSIONS AND RELEVANCE

These results suggest that exposure to ALAN while sleeping may be a risk factor for weight gain and development of overweight or obesity. Further prospective and interventional studies could help elucidate this association and clarify whether lowering exposure to ALAN while sleeping can promote obesity prevention.

Rotating night shift work and menopausal age

STUDY QUESTION

How are rotating night shift schedules associated with age at menopause among a large, national cohort of shift working nurses?

SUMMARY ANSWER

Our findings suggest that working rotating night shifts with sufficient frequency may modestly accelerate reproductive senescence among women who may already be predisposed to earlier menopause.

WHAT IS KNOWN ALREADY

Younger age at menopause has been associated with increased risk of adverse health outcomes, particularly those linked to reproduction. Night work has been associated with reproductive dysfunction, including disruption of menstrual cycle patterns.

STUDY DESIGN, SIZE, DURATION

This cohort study was conducted among 80 840 women of the Nurses' Health Study 2 (NHS2), with prospective follow-up from 1991 through 2013. Loss-to-follow-up of the NHS2 is estimated to be <10%.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We assessed the association between cumulative and current rotating night shift work and age at natural menopause over 22 years of follow-up (1991-2013). Cox proportional hazards models were used to estimate hazard ratios (HR) for menopause, adjusted for age, smoking status, body mass index, physical activity, alcohol consumption, reproductive factors and exogenous hormone use.

MAIN RESULTS AND THE ROLE OF CHANCE

Over follow-up, 27 456 women (34%) reached natural menopause. Women who worked 20 or more months of rotating night shifts in the prior 2-year had an increased risk of earlier menopause (multivariable-adjusted (MV)-HR = 1.09, 95% CI: 1.02-1.16) compared to women without rotating night shift work. This risk was stronger among women undergoing menopause or otherwise censored under age 45 years (MV-HR = 1.25, 95% CI: 1.08-1.46), than it was for those continuing in the study when >45 years old (MV-HR = 1.05, 95% CI: 0.99-1.13). Working 10 or more years of cumulative rotating night work was also associated with higher risk of menopause among women reaching menopause under age 45 (MV-HR10-19 years = 1.22, 95% CI: 1.03-1.44; MV-HR≥20 years = 1.73, 95% CI: 0.90-3.35), though not over the age of 45 years (MV-HR10-19 years = 1.04, 95% CI: 0.99-1.10; MV-HR≥20 years = 1.01, 95% CI: 0.89-1.15).

LIMITATIONS, REASONS FOR CAUTION

The degree to which observed effects of rotating night shifts on age at natural menopause are due to circadian disruption, rather than fatigue and stress associated with working more demanding schedules, is uncertain due to potential residual confounding by these factors.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to assess the effects of night work on menopausal timing among a larger national cohort of shift working women. Women already prone to earlier menopause may further truncate their reproductive lifetime by working schedules comprising day as well as night shifts.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Center for Disease Control and Prevention/The National Institute for Occupational Safety and Health Grant 5R01OH009803 (PI: Schernhammer E), as well as UM1 CA176726 from the National Institute of Health. The funding sources had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review or approval of the article; and decision to submit the article for publication. The authors have no conflicts of interest.

A multicenter randomized controlled trial for bright light therapy in adults with intellectual disabilities and depression: Study protocol and obstacle management

Due to the limited cognitive and communicative abilities of adults with intellectual disabilities (ID), current treatment options for depression are often limited to lifestyle changes and pharmacological treatment. Bright light therapy (BLT) is an effective intervention for both seasonal and non-seasonal depression in the general population. BLT is an inexpensive, easy to carry out intervention with minimal side effects. However, knowledge on its anti-depressant effect in adults with ID is lacking. Obstacles in realizing a controlled intervention study in this particular study population may have contributed to this lack. To study the effect of BLT on depression in this population, it is necessary to successfully execute a multicenter randomized controlled trial (RCT). Therefore, the study protocol and the management of anticipated obstacles regarding this trial are presented.

Is afternoon cortisol more reliable than waking cortisol in association studies of children with an ASD?

Salivary cortisol may be used as a biomarker of stress and anxiety in children with an Autism Spectrum Disorder (ASD) and is particularly valuable in studies of the association between stress-related cortisol concentrations and other factors such as comorbid disorders or aspects of the ASD phenotype. Although protocols for the collection of cortisol shortly after waking are often based on the assumption of the presence of a diurnal rhythm in cortisol, that rhythm may not be as reliable in children with an ASD as in non-ASD children. Alternatively, collecting cortisol during the afternoon may represent a more reliable procedure with less inter-participant variability.

Impact of different colours of artificial light at night on melatonin rhythm and gene expression of gonadotropins in European perch

The distribution and intensity of artificial light at night, commonly referred to as light pollution, is consequently rising and progressively also ecological implications come to light. Low intensity light is known to suppress nocturnal melatonin production in several fish species. This study aims to examine the least suppressive light colour for melatonin excreted into the holding water and the influence of different light qualities and quantities in the night on gene expression of gonadotropins in fish. European perch (Perca fluviatilis) were exposed to light of different wavelengths during the night (blue, green, and red). Melatonin concentrations were measured from water samples every 3h during a 24h period. Gene expression of gonadotropins was measured in perch exposed to different light colours and was additionally examined for perch subjected to different intensities of white light (0 lx, 1 lx, 10 lx, 100 lx) during the night. All different light colours caused a significant drop of melatonin concentration; however, blue light was least suppressive. Gene expression of gonadotropins was not influenced by nocturnal light of different light colours, but in female perch gonadotropin expression was significantly reduced by white light already at the lowest level (1 lx). We conclude that artificial light with shorter wavelengths at night is less effective in disturbing biological rhythms of perch than longer wavelengths, coinciding with the light situation in freshwater habitats inhabited by perch. Different light colours in the night showed no significant effect on gonadotropin expression, but white light in the night can disturb reproductive traits already at very low light intensities. These findings indicate that light pollution has not only the potential to disturb the melatonin cycle but also the reproductive rhythm and may therefore have implications on whole species communities.

The effects of light at night on circadian clocks and metabolism

Most organisms display endogenously produced ∼ 24-hour fluctuations in physiology and behavior, termed circadian rhythms. Circadian rhythms are driven by a transcriptional-translational feedback loop that is hierarchically expressed throughout the brain and body, with the suprachiasmatic nucleus of the hypothalamus serving as the master circadian oscillator at the top of the hierarchy. Appropriate circadian regulation is important for many homeostatic functions including energy regulation. Multiple genes involved in nutrient metabolism display rhythmic oscillations, and metabolically related hormones such as glucagon, insulin, ghrelin, leptin, and corticosterone are released in a circadian fashion. Mice harboring mutations in circadian clock genes alter feeding behavior, endocrine signaling, and dietary fat absorption. Moreover, misalignment between behavioral and molecular circadian clocks can result in obesity in both rodents and humans. Importantly, circadian rhythms are most potently synchronized to the external environment by light information and exposure to light at night potentially disrupts circadian system function. Since the advent of electric lights around the turn of the 20th century, exposure to artificial and irregular light schedules has become commonplace. The increase in exposure to light at night parallels the global increase in the prevalence of obesity and metabolic disorders. In this review, we propose that exposure to light at night alters metabolic function through disruption of the circadian system. We first provide an introduction to the circadian system, with a specific emphasis on the effects of light on circadian rhythms. Next we address interactions between the circadian system and metabolism. Finally, we review current experimental and epidemiological work directly associating exposure to light at night and metabolism.

Exposure to bright light during evening class hours increases alertness among working college students

OBJECTIVE

To evaluate the effects of exposure to bright light on sleepiness during evening hours among college students.

METHODS

Twenty-seven healthy college students, all males, with ages ranging from 21 to 24years, working during the day and studying in the evening, participated in this study. During the 3week study, the students wore actigraphs and recorded levels of sleepiness. In a crossover design, on the second and third weeks, the students were exposed to bright light (BL) at either 19:00 or 21:00h. Salivary melatonin samples were collected before and after BL exposure. ANOVA test for repeated measurements were performed.

RESULTS

After BL exposure, sleepiness levels were reduced at 20:30 and 22:00h (F=2.2; p<0.05). ANOVA showed statistical differences between time (F=4.84; p=0.04) and between day and time of BL exposure (F=4.24; p=0.05). The results showed effects of melatonin onset at 20:00 and 21:30h and sleepiness levels (F=7.67; p=0.02) and perception of sleepiness and intervention time (F=6.52; p=0.01).

CONCLUSION

Controlled exposure to BL during evening hours increased alertness among college students. The effects of BL on sleepiness varied according to the time of melatonin onset.

Caracterização e distribuição de cronotipos no sul do Brasil: diferenças de gênero e estação de nascimento

OBJETIVO: Investigar a tipologia circadiana e as diferenças de gênero em universitários do sul do Brasil. MÉTODOS: Voluntários (736) de 17 a 49 anos preencheram a versão brasileira do Questionário de Cronotipo (QC), tradução do Morningness-eveningness Questionnaire (MEQ) de Horne e Östberg. Medidas de tendência central e dispersão e curva de distribuição dos escores do QC (Kolmogorov-Smirnov) foram calculadas de acordo com gênero (teste t de Student), idade, estação de nascimento e desconforto com o horário de verão (qui-quadrado). RESULTADOS: Foram incluídos 648 indivíduos (36% homens, 64% mulheres), com perdas de 12% por questionários incorretos. A distribuição dos escores do QC evidenciou uma curva normal (amplitude = 18-77; média = 46,6; desvio-padrão = 10,8). Nesta amostra, 32% foram vespertinos, 54% intermediários e 14% matutinos. As médias do QC foram significativamente diferentes (p = 0,003): homens (44,9 ± 10,8) comparados com mulheres (47,5 ± 10,7) e 70% dos que nasceram na primavera e no verão foram vespertinos (p = 0,015), sem associação gênero-estação do ano. CONCLUSÃO: Homens e nascidos na primavera-verão evidenciaram preferência pela vespertinidade, não havendo diferença de gênero com relação à estação de nascimento. Nossos resultados estão de acordo com estudos realizados no hemisfério norte que mostraram, também, uma associação entre a estação de nascimento e o cronotipo.

Further support for higher salivary cortisol levels in "morning" compared to "evening" persons

We analyzed free cortisol daytime levels in a "3-days-7-samples-a-day" protocol in relation to morningness in 112 middle-aged male and female adults derived from the first year of data of the Trier Teacher Stress Study using a one-item proxy for the assessment of chronotype. First, log-transformed cortisol levels were analyzed by a repeated-measures approach controlling for relevant covariates. Results yielded an almost significant main effect of morningness (P=.06). Subsequent within-day analyses, additionally controlling for awakening time, resulted in (marginally) significant main effects of morningness at Day 1 (P=.06) and Day 3 (P=.05) and a significant interaction of sample-by-morningness at Day 2 (P=.04). In sum, the present data seem to corroborate the idea of higher daytime cortisol levels in morning relative to evening types in a sample of healthy middle-aged male and female adults.

Melatonin and human rhythms

Melatonin signals time of day and time of year in mammals by virtue of its pattern of secretion, which defines 'biological night.' It is supremely important for research on the physiology and pathology of the human biological clock. Light suppresses melatonin secretion at night using pathways involved in circadian photoreception. The melatonin rhythm (as evidenced by its profile in plasma, saliva, or its major metabolite, 6-sulphatoxymelatonin [aMT6s] in urine) is the best peripheral index of the timing of the human circadian pacemaker. Light suppression and phase-shifting of the melatonin 24 h profile enables the characterization of human circadian photoreception, and circulating concentrations of the hormone are used to investigate the general properties of the human circadian system in health and disease. Suppression of melatonin by light at night has been invoked as a possible influence on major disease risk as there is increasing evidence for its oncostatic effects. Exogenous melatonin acts as a 'chronobiotic.' Acutely, it increases sleep propensity during 'biological day.' These properties have led to successful treatments for serveal circadian rhythm disorders. Endogenous melatonin acts to reinforce the functioning of the human circadian system, probably in many ways. The future holds much promise for melatonin as a research tool and as a therapy for various conditions.