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How sleep regulates physiological stress in healthy individuals is not well understood. We explored the associations between naturally occurring pre-sleep physiological arousal and EEG power spectral density together with rapid eye movement sleep (REMS) continuity. One hundred and fifty-four individuals (mean age 16.9, SD 0.1 years) collected five samples of saliva between the evening (mean time 18:20) and bedtime (mean 23:00) by using swabs, and underwent an overnight in-home polysomnography. We calculated spectral density for REMS and non-rapid eye movement sleep (non-REMS), and the number and duration of REMS arousals (<15 s) during sleep. An observational design allowed for measurement of natural variation in physiological and sleep arousal. Increasing cortisol levels toward bedtime were associated with higher EEG power spectral density at all frequency ranges in frontal locations, the highest association being for the beta1 frequency band. In central locations, the associations were pronounced for beta1 and beta2 bands. Higher overall cortisol levels in the evening were associated with less fragmented REMS. Presleep arousal was not associated with sleep staging. Physiological arousal toward bedtime was associated with EEG power spectral density values during sleep specifically at high EEG frequencies. This may represent a compensatory mechanism that serves as an adaptation to stress, since the REMS was more continuous along a higher physiological arousal level in the evening. Although causality cannot be inferred, a design with nonmanipulated physiological stress followed by naturally timed sleep at home provides new insights into stress regulation homeostasis.

Light is necessary for life, and artificial light improves visual performance and safety, but there is an increasing concern of the potential health and environmental impacts of light. Findings from a number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing further health impacts. However, a variety of methods has been applied in individual experimental studies of light-induced circadian impacts, including definition of light exposure and outcomes. Thus, a systematic review is needed to synthesize the results. In addition, a review of the scientific evidence on the impacts of light on circadian rhythm is needed for developing an evaluation method of light pollution, i.e., the negative impacts of artificial light, in life cycle assessment (LCA). The current LCA practice does not have a method to evaluate the light pollution, neither in terms of human health nor the ecological impacts. The systematic literature survey was conducted by searching for two concepts: light and circadian rhythm. The circadian rhythm was searched with additional terms of melatonin and rapid-eye-movement (REM) sleep. The literature search resulted to 128 articles which were subjected to a data collection and analysis. Melatonin secretion was studied in 122 articles and REM sleep in 13 articles. The reports on melatonin secretion were divided into studies with specific light exposure (101 reports), usually in a controlled laboratory environment, and studies of prevailing light conditions typical at home or work environments (21 studies). Studies were generally conducted on adults in their twenties or thirties, but only very few studies experimented on children and elderly adults. Surprisingly many studies were conducted with a small sample size: 39 out of 128 studies were conducted with 10 or less subjects. The quality criteria of studies for more profound synthesis were a minimum sample size of 20 subjects and providing details of the light exposure (spectrum or wavelength; illuminance, irradiance or photon density). This resulted to 13 qualified studies on melatonin and 2 studies on REM sleep. Further analysis of these 15 reports indicated that a two-hour exposure to blue light (460 nm) in the evening suppresses melatonin, the maximum melatonin-suppressing effect being achieved at the shortest wavelengths (424 nm, violet). The melatonin concentration recovered rather rapidly, within 15 min from cessation of the exposure, suggesting a short-term or simultaneous impact of light exposure on the melatonin secretion. Melatonin secretion and suppression were reduced with age, but the light-induced circadian phase advance was not impaired with age. Light exposure in the evening, at night and in the morning affected the circadian phase of melatonin levels. In addition, even the longest wavelengths (631 nm, red) and intermittent light exposures induced circadian resetting responses, and exposure to low light levels (5-10 lux) at night when sleeping with eyes closed induced a circadian response. The review enables further development of an evaluation method of light pollution in LCA regarding the light-induced impacts on human circadian system.

A preference for eveningness (being a "night owl") and preterm birth (<37 weeks of gestation) are associated with similar adversities, such as elevated blood pressure, impaired glucose regulation, poorer physical fitness, and lower mood. Yet, it remains unclear if and how preterm birth is associated with circadian preference. The aim of this study was to assess this association across the whole gestation range, using both objective and subjective measurements of circadian preference. Circadian preference was measured among 594 young adults (mean age 24.3 years, SD 1.3) from two cohorts: the ESTER study and the Arvo Ylppö Longitudinal Study. We compared 83 participants born early preterm (<34 weeks) and 165 late preterm (34 to <37 weeks) with those born at term (≥37 weeks, n = 346). We also compared very low birth weight (VLBW, <1500 g) participants with term-born controls. We obtained objective sleep data with actigraphs that were worn for a mean period of 6.8 (SD 1.4) nights. Our primary outcome was sleep midpoint during weekdays and weekend. The sleep midpoint is the half-way time between falling asleep and waking up, and it represents sleep timing. We also investigated subjective chronotype with the Morningness-Eveningness Questionnaire (MEQ) in 688 (n = 138/221/329) ESTER participants. The MEQ consists of 19 questions, which estimates the respondent to be of a "morning", "evening," or "intermediate" chronotype, based on the Morningness-Eveningness Score (MES). We analyzed the data from the actigraphs and the MES with three linear regression models, and analyzed distribution of the chronotype class with Pearson χ2. There were no consistent differences across the study groups in sleep midpoint. As compared with those born at term, the mean differences in minutes:seconds and 95% confidence intervals for the sleep midpoint were: early preterm weekdays 11:47 (-8:34 to 32:08), early preterm weekend 4:14 (-19:45 to 28:13), late preterm weekdays -10:28 (-26:16 to 5:21), and late preterm weekend -1:29 (-20:36 to 17:37). There was no difference in sleep timing between VLBW-participants and controls either. The distribution of chronotype in the MEQ among all participants was 12.4% morningness, 65.4% intermediate, and 22.2% eveningness. The distribution of the subjective chronotype class did not differ between the three gestational age groups (p = 0.98). The linear regression models did not show any influence of gestational age group or VLBW status on the MES (all p > 0.5). We found no consistent differences between adults born early or late preterm and those born at term in circadian preference. The earlier circadian preference previously observed in those born smallest is unlikely to extend across the whole range of preterm birth.

Circadian preference toward eveningness has been associated with increased risk for mental health problems both in early adolescence and in adulthood. However, in late adolescence, when circadian rhythm naturally shifts to later, its significance for mental health is not clear. Accordingly, we studied how circadian rhythm estimated both by self-reported chronotype and by actigraph-defined midpoint of sleep was associated with self-reported psychiatric problems based on Youth Self Report (YSR). The study builds on a community cohort born in 1998, Helsinki, Finland. At age 17 years (mean age = 16.9, SD = 0.1 years), 183 adolescents (65.6% of the invited) participated in the study. We used the shortened version of the Horne-Östberg morningness-eveningness Questionnaire to define the chronotype, and actigraphs to define the naturally occur circadian rhythm over a 4 to 17 days' period (mean nights N = 8.3, SD = 1.8). The Achenbach software was used to obtain T-score values for YSR psychiatric problem scales. The analyses were adjusted for important covariates including gender, socioeconomic status, body mass index, pubertal maturation, mother's licorice consumption during pregnancy, and actigraph-defined sleep duration and quality. Eveningness was associated with higher scores in rule-breaking behavior and conduct problems (as assessed either by midpoint of sleep or by self-reported chronotype, p-values <0.05), attention deficit/hyperactivity problems (by self-reported chronotype, p-values <0.05), with affective problems (by midpoint of sleep and by self-reported chronotype, p-values <0.05) and somatic complaints (by self-reported chronotype, p-values <0.05), as compared to circadian tendency toward morningness. Our results suggest that the association between eveningness and externalizing problem behavior, present in children and younger adolescents, is also present in late adolescence when circadian rhythms shift toward evening.

Introduction: Both short and long sleep duration may increase risk of type 2 diabetes (diabetes). We studied if short and long sleep durations were associated with insulin resistance (IR) and insulin secretion in individuals without diabetes, and if the associations remained after we excluded individuals who reported more frequent and severe complaints of sleep apnea and insomnia., Participants and Methods: An oral glucose tolerance test (OGTT) was performed for 722 adults without diabetes. Indices of IR and insulin secretion were calculated. Sleep duration and complaints of sleep apnea and insomnia were self-reported., Results: In comparison to average sleepers (6-9 h/night), short sleepers (< 6 h/night) had higher 120-min insulin and AUC glucose, and long sleepers (≥ 9 h/night) had higher fasting and 120-min insulin, 120-min glucose, and HOMAIR and lower Insulin Sensitivity Index. After adjusting for confounders and after excluding individuals who reported more frequent and severe complaints of sleep apnea and insomnia, long sleep duration remained significantly associated with IR and insulin secretion., Discussion: Long but not short sleep duration is associated with IR and insulin secretion in individuals without diabetes whether or not accompanied by sleep complaints. Long sleepers may benefit from targeted preventions and interventions that aim at reducing risk of future diabetes.

Background: Hypertensive disorders may affect the fetal developmental milieu and thus hint at mechanisms by which prenatal adversity associates with poorer intellectual ability in subsequent life., Aim: We tested if hypertensive disorders in pregnancy are associated with intellectual ability in the offspring in young adulthood and if any potential associations between hypertensive disorders and intellectual abilities differ according to length of gestation, birth-weight, parity, and childhood socio-economic background., Methods: Using mothers' blood pressure and urinary protein measurements at maternity clinics and birth hospitals, we defined normotensive or hypertensive pregnancies in mothers of 1,196 men who participated in the Helsinki Birth Cohort 1934-1944 Study. At age 20 years the men completed a test on intellectual abilities during compulsory military service., Results: Participants born after pregnancies complicated by hypertensive disorders scored lower on intellectual abilities compared to those born after normotensive pregnancies. The effects of hypertensive disorders were most obvious in men born preterm or after a primiparous pregnancy and in men of higher childhood socio-economic background., Conclusion: Hypertensive disorders in pregnancy are, albeit weakly, associated with lower intellectual abilities in the offspring. These findings are compatible with the concept of adverse fetal 'programming' by a suboptimal prenatal environment.

A suboptimal prenatal environment may induce permanent changes in cells, organs and physiology that alter social, emotional and cognitive functioning, and increase the risk of cardiometabolic and mental disorders in subsequent life ("developmental programming"). Although animal studies have provided a wealth of data on programming and its mechanisms, including on the role of stress and its glucocorticoid mediators, empirical evidence of these mechanisms in humans is still scanty. We review the existing human evidence on the effects of prenatal maternal stress, anxiety and depression, glucocorticoids and intake of liquorice (which inhibits the placental barrier to maternal glucocorticoids) on offspring developmental outcomes including, for instance, alterations in psychophysiological and neurocognitive functioning and mental health. This work lays the foundations for biomarker discovery and affords opportunities for prevention and interventions to ameliorate adverse outcomes in humans.

INTRODUCTION. Socio-economic position (SEP) is a powerful source of health inequality. Less is known of early life conditions that may determine the course of adult SEP. We tested if early life stress (ELS) due to a separation from the parents during World War II predicts adult SEP, trajectories of incomes across the entire working career, and inter-generational social mobility. MATERIALS AND METHODS. Participants (n = 10,702) were from the Helsinki Birth Cohort Study 1934-44. Compared to the non-separated, the separated individuals attained a lower SEP in adulthood. The separated whose fathers were manual workers were less likely to be upwardly mobile from paternal occupation category to higher categories of own occupation, education, and incomes. The separated whose fathers had junior and senior clerical occupations were more likely to be downwardly mobile. Comparison of trajectories of incomes across adulthood showed that the difference between the separated and the non-separated grew larger across time, such that among the separated the incomes decreased. CONCLUSIONS. This life-course study shows that severe ELS due to a separation from parents in childhood is associated with socio-economic disadvantage in adult life. Even high initial SEP in childhood may not protect from the negative effects of ELS.

Background: Relatively little is known about the significance of normal variation in objectively assessed sleep duration and its regularity in children's psychological well-being., Purpose: We explored the associations between sleep duration and regularity and behavioral and emotional problems in 8-year-old children., Methods: A correlational design was applied among an epidemiological sample of children born in 1998. Sleep was registered with an actigraph for seven nights (range 3 to 14) in 2006. Mothers (n = 280) and fathers (n = 190) rated their child's behavioral problems with the Child Behavior Checklist., Results: Children with short sleep duration had an increased risk for behavioral problems, thought problems, and Diagnostic and Statistical Manual of Mental Disorders, 4th Edition-based attention-deficit hyperactivity problems according to maternal ratings. Based on paternal ratings, short sleep duration was associated with more rule-breaking and externalizing symptoms. Irregularity in sleep duration from weekdays to weekends was associated with an increased risk for specifically internalizing symptoms in paternal ratings., Conclusions: The results highlight the importance of sufficient sleep duration and regular sleep patterns from weekdays to weekends. Short sleep duration was associated specifically with problems related to attentional control and externalizing behaviors, whereas irregularity in sleep duration was, in particular, associated with internalizing problems.

The authors explored morningness-eveningness propensity in adults born prematurely at very low birth weight (VLBW;  < 1500g) and in controls born at term. At age 21 to 29 yrs, 184 participants completed the Morningness-Eveningness Questionnaire (MEQ). Compared with controls, VLBW adults scored higher in morningness propensity (group difference: 2.8 scores, 95% confidence interval: 0.1 to 5.5; p = .042). This finding was confined to those VLBW adults whose birth weight was not small for gestational age, and remained similar when adjusting for age, sex, and working conditions. The finding is potentially important, since morningness is associated with beneficial health outcomes.

Background: Early life experiences might have long-term effects on health., Aim: To assess prevalence of cardiovascular disease and diabetes in later life among individuals exposed to traumatic separation in early childhood due to World War II., Methods: Of the participants of the Helsinki Birth Cohort 1934-44 Study (n=2003), 320 had been evacuated abroad to temporary foster care in childhood. The remaining participants served as controls. The mean age at evacuation was 4.8 (SD=2.4) years and the mean duration of the evacuation was 1.7 (SD=1.0) years., Results: Cardiovascular morbidity was higher among the former war evacuees (14.7% versus 7.9%; odds ratio (OR)=2.0, 95% confidence interval (95% CI) 1.4-2.9; P<0.001). A similar difference in prevalence of type 2 diabetes was observed (19.7% versus 14.8%; OR=1.4, 95% CI 1.1-1.9, P=0.025). The former war evacuees were also more likely to be hypertensive (P<0.05). The effects on morbidity were not explained by age at testing or socio-economic circumstances in childhood or adulthood., Conclusion: Early life traumatic events may extend lifelong effects on health. This study is among the first to show that early life trauma predicts higher prevalence of cardiovascular disease and type 2 diabetes in late adulthood, in a longitudinal clinical study setting.