Subjective sleep onset latency is influenced by sleep structure and body heat loss in human subjects.

The present study examined the relationship between subjective sleep onset latency (SOL), sleep structure, changes in skin and body temperature, and subjective evaluation of sleep in healthy young adults to elucidate the pathophysiological mechanisms of insomnia. A total of 28 participants (age 21.54 [0.50] years) with no sleep problems participated in a 1-h polysomnographic recording that obtained objective sleep parameters during the daytime while skin and body temperatures were recorded. The distal-proximal skin temperature gradient (DPG) was calculated. Subjective parameters, such as subjective SOL, sleep time, and restorative sleepiness, were evaluated before and after sleep. Most participants estimated their sleep latency as being longer than their actual SOL (13.7 versus 7.6 min). Objective SOL was significantly correlated with each sleep stage parameter whereas subjective SOL was negatively correlated with Stage N2 sleep duration (Rho = -0.454, p = 0.020), slow-wave activity and delta power (Rho = -0.500, p = 0.011 and Rho = -0.432, p = 0.031, respectively), and ΔDPG (the degree of reduction of heat loss before and after lights-off). Stepwise regression analysis showed that ΔDPG was the strongest predictive factor in explaining the length of subjective SOL. The degree of heat dissipation before and after lights-off contributed most to the sensation of falling asleep in healthy young adults. This finding may be helpful for elucidating the physiological mechanisms of insomnia and its treatment.

The effect of nonrestorative sleep on incident hypertension 1-2 years later among middle-aged Hispanics/Latinos.

BACKGROUND: Insomnia is known to be a major risk factor for incident hypertension. Nonrestorative sleep (NRS), which refers to insufficiently rested sleep, has reported to associate with various diseases. This study aimed to investigate the longitudinal association between insomnia-related symptoms including NRS and incident hypertension 1-2 years later by age group (young, 18-39 years and middle-age, 40-64 years) using existing cohort data involving Hispanics/Latinos. METHODS: This study included 1100 subjects who had participated in both the Hispanic Community Health Study/Study of Latinos and its follow-up study, the Sueño Ancillary Study, and met additional eligibility criteria. Incident hypertension was assessed by self-reported history and/or the use of antihypertensives. The Women's Health Initiative Insomnia Rating Scale (WHIIRS) was used to evaluate insomnia-related symptoms (difficulty initiating sleep, difficulty maintaining sleep, early morning awakening, difficulty returning to sleep, and NRS). Logistic regression analyses were conducted to assess the degree to which insomnia-related symptoms at baseline predicted incident hypertension. RESULTS: Among the participants (64% middle-aged, 36% young adults), 140 (12.7%) developed hypertension during the follow-up period. Among the sleep-related symptoms, only NRS predicted incident hypertension after adjusting for sociodemographic factors and physical condition (odds ratio: 1.88, 95% confidence interval: 1.10-3.21, p = 0.022) in middle-aged adults. None of the insomnia-related symptoms were associated with incident hypertension in the young adults. No association was found between WHIIRS-defined insomnia (total score ≥ 9) and incident hypertension in middle-aged adults or young adults. CONCLUSION: The present findings suggest the importance of focusing on NRS to help prevent the development of hypertension in middle-aged adults.

The association between subjective-objective discrepancies in sleep duration and mortality in older men.

A discrepancy in subjective and objective estimations of sleep duration, which often diverge, could have long-term adverse effects on health outcomes in older adults. Using data from 2674 older adult men (≥ 65 years of age) of the Osteoporotic Fractures in Men Sleep Study, we assessed the longitudinal association between misperception index (MI), calculated as MI = (objective sleep duration - subjective sleep duration)/objective sleep duration, and all-cause mortality. During the follow-up with a mean (standard deviation) of 10.8 (4.2) years, 1596 deaths were observed. As a continuous variable, MI showed a linear relationship with all-cause mortality after adjusting for multiple covariates, including polysomnography-measured objective sleep duration [fully adjusted hazard ratio (HR), 0.69; 95% confidence interval [CI], 0.56-0.84]. As a categorical variable, the lowest MI quartile (vs. the interquartile MI range) was associated with increased mortality (fully adjusted HR, 1.28; 95% CI, 1.12-1.46), whereas the highest MI quartile was not associated with mortality (fully adjusted HR, 0.97; 95% CI, 0.85-1.11). The subjective overestimation of sleep duration may be a risk factor for all-cause mortality in older men. Future studies should examine why subjective overestimation of sleep duration is associated with all-cause mortality from a physiological perspective.

Associations of nonrestorative sleep and insomnia symptoms with incident depressive symptoms over 1-2 years: Longitudinal results from the Hispanic Community Health Study/Study of Latinos and Sueño Ancillary Study.

BACKGROUND: Nonrestorative sleep (NRS), defined as insufficiently rested or refreshed sleep, is considered to play an important role in the development of depression. The aim of this study is to investigate the predictive ability of insomnia-related symptoms, including NRS, for incident depressive symptoms (DEPs) in a longitudinal manner. METHODS: We used data of 1196 samples aged 18-64 years who participated in both the Hispanic Community Health Study/Study of Latinos conducted in 2008-2010 and the follow-up study (Sueño Ancillary Study) conducted in 2010-2013. DEPs and insomnia-related symptoms (difficulty initiating sleep [DIS], difficulty maintaining sleep [DMS], early morning awakening [EMA], difficulty returning to sleep [DRS], and NRS) were evaluated by the 10-item Center for Epidemiologic Studies Depression Scale and the Women's Health Initiative Insomnia Rating Scale, respectively. A logistic regression analysis was used to evaluate the predictive ability of each insomnia-related symptom at baseline for incident DEPs in couple-years. RESULTS: In the univariate logistic regression analysis, all insomnia-related symptoms had significant associations with incident DEPs (DIS, odds ratio [OR] = 1.6; DMS, OR = 1.6; EMA, OR = 1.5; DRS, OR = 1.9; NRS, OR = 2.5). After adjusting for sociodemographic factors and the confounding effects of other insomnia-related symptoms, only NRS (OR = 2.2, 95% confidence interval = 1.4-3.5, p = .001) was significantly associated with incident DEPs. CONCLUSIONS: NRS was a risk factor for incident DEPs, which includes a predictive ability for other insomnia-related symptoms. Our results suggest that focusing on NRS is an effective strategy for preventing depression in public health promotions.

Mortality associated with nonrestorative short sleep or nonrestorative long time-in-bed in middle-aged and older adults.

Associations of sleep duration with human health could differ depending on whether sleep is restorative. Using data from 5804 participants of the Sleep Heart Health Study, we examined the longitudinal association of sleep restfulness combined with polysomnography-measured total sleep time (TST) or time in bed (TIB), representing different sleeping behaviors, with all-cause mortality. Among middle-aged adults, compared with restful intermediate TST quartile, the lowest TST quartile with feeling unrested was associated with higher mortality (hazard ratio [HR], 1.54; 95% confidence interval [CI] 1.01-2.33); the highest TST quartile with feeling rested was associated with lower mortality (HR, 0.55; 95% CI 0.32-0.97). Among older adults, the highest TIB quartile with feeling unrested was associated with higher mortality, compared with restful intermediate TIB quartile (HR, 1.57; 95% CI 1.23-2.01). Results suggest a role of restorative sleep in differentiating the effects of sleep duration on health outcomes in midlife and beyond.

Association of Subjective Quality and Quantity of Sleep with Quality of Life among a General Population.

This study aimed to determine whether both subjective sleep quality and sleep duration are directly associated with quality of life (QOL), as well as indirectly associated with QOL through insomnia symptoms. Individuals aged 20-69 years without mental illness (n = 9305) were enrolled in this web-based cross-sectional survey. The Short Form-8 was used to assess physical and mental QOL. We used the Pittsburgh Sleep Quality Index (PSQI) and extracted items related to subjective sleep quality and sleep duration. Insomnia symptoms were also extracted from the PSQI. The hypothesized models were tested using structural equation modeling. Worse sleep quality, but not shorter sleep duration, was related to worse physical QOL. Both worse sleep quality and shorter sleep duration were related to worse mental QOL. Insomnia symptoms mediated these relationships. Subgroup analyses revealed a U-shaped relationship between sleep duration and physical/mental QOL. However, the relationship between sleep quality and physical/mental QOL was consistent regardless of sleep duration. The results suggest that subjective sleep quality has a more coherent association with QOL than subjective sleep duration. Because of its high feasibility, a questionnaire on overall sleep quality could be a useful indicator in future epidemiological studies of strategies for improving QOL.

Periocular skin warming promotes body heat loss and sleep onset: a randomized placebo-controlled study.

Periocular skin warming was reported to have favorable effects on subjective and objective sleep quality. We hypothesized that enhancing body heat loss by periocular skin warming would reduce sleep onset and improve sleep quality. Eighteen healthy volunteers were asked to maintain wakefulness with their eyes closed for 60 min after applying either a warming or sham eye mask, followed by a 60-min sleep period. Compared to the sham, periocular warming increased the distal skin temperature and distal-proximal skin temperature gradient only during the 30-min thermal manipulation period. In the subsequent sleep period, periocular warming facilitated sleep onset, increased stage 2 sleep and electroencephalographic delta activity during the first half of the sleep period relative to the sham. These results suggest that periocular skin warming may accelerate and deepen sleep by enhancing physiological heat loss via the distal skin, mimicking physiological conditions preceding habitual sleep.

Diurnal repeated exercise promotes slow-wave activity and fast-sigma power during sleep with increase in body temperature: a human crossover trial.

The effects of exercise on sleep have been explored from various perspectives, but little is known about how the effects of acute exercise on sleep are produced through physiological functions. We used a protocol of multiple daytime sessions of moderate-intensity aerobic exercise and examined the subsequent effects on sleep structure, core body temperature (CBT), distal-proximal skin temperature gradient (DPG), and subjective parameters. Fourteen healthy men who did not exercise regularly were evaluated under the baseline (no exercise) and exercise conditions on a within-subject crossover basis. Under the exercise condition, each participant performed a 40-min aerobic workout at 40% of maximal oxygen intake, four times between morning and early evening. We observed a 33% increase in slow-wave sleep (SWS; P = 0.005), as well as increases in slow-wave activity (SWA; P = 0.026), the fast-sigma power/SWA ratio (P = 0.005), and subjective sleep depth and restorativeness the following morning. Moreover, both CBT and the DPG increased during sleep after exercise (P = 0.021 and P = 0.047, respectively). Regression analysis identified an increased nocturnal DPG during sleep after exercise as a factor in the increase in SWA. The fast-sigma/SWA ratio correlated with CBT. The performance of acute exercise promotes SWS with nocturnal elevation in the DPG. Both CBT and fast-sigma power may play a role in the specific physiological status of the body after exercise. NEW & NOTEWORTHY We used multiple daytime sessions of moderate-intensity aerobic exercise to examine the effects on the sleep structure, core body temperature (CBT), distal-proximal skin temperature gradient (DPG), and subjective parameters. Significant increases in slow-wave activity (SWA), CBT, DPG, fast-sigma power, and subjective parameters were observed during the night and the following morning. Nocturnal DPG is a factor in the increased SWA.

Periocular skin warming elevates the distal skin temperature without affecting the proximal or core body temperature.

Periocular skin warming reportedly improves the objective and subjective sleep quality in adults with mild difficulty in falling asleep. To clarify the effects of periocular warming, we examined the distal skin temperatures (hands and feet), proximal skin temperature (infraclavicular region) and core body temperature as well as the distal-proximal skin temperature gradient (DPG). Nineteen healthy males underwent two experimental sessions, wherein they used a warming or sham eye mask under a semi-constant routine protocol in a crossover manner. Participants were instructed to maintain wakefulness with their eyes closed for 60 minutes after wearing the eye mask. The warming eye mask increased the periocular skin temperature to 38-40 °C for the first 20 minutes, whereas the temperature remained unchanged with the sham mask. Compared to that of the sham eye mask, the warming eye mask significantly increased the temperatures of the hands and feet and the DPG, whereas the proximal skin and core body temperatures were unaffected. Subjective sleepiness and pleasantness were significantly increased by the warming eye mask. These results represent physiological heat loss associated with sleep initiation without affecting the proximal skin or core body temperatures, suggesting that thermal stimulation in certain areas can provoke similar changes in remote areas of the body.

Change in frequency of periodic limb movements during sleep with usage of continuous positive airway pressure in obstructive sleep apnea syndrome.

Periodic limb movements during sleep (PLMS) sometimes newly appear on the night of continuous positive airway pressure (CPAP) titration in patients with obstructive sleep apnea syndrome (OSAS). To ascertain the incidence and causative factors of this phenomenon, we investigated differences in its prevalence and the factors associated with newly appeared and persistent PLMS on CPAP titration night. We retrospectively analyzed polysomnographic data of 997 consecutive OSAS outpatients who had undergone overnight CPAP titration. On the basis of changes in periodic limb movements index (PLMI) values (cut off level≥15/h) from baseline polysomnography (BPSG) to CPAP titration PSG, patients were assigned to one of four groups: persistent, CPAP-emergent, CPAP-disappeared, and non-PLMS. The rate of patients was 6.7% in the persistent group, 8.0% in the CPAP-emergent group, 4.0% in the CPAP-disappearance group, and 81.2% in the non-PLMS group. Multivariate logistic regression analysis revealed that a higher apnea-hypopnea index (AHI) on BPSG and ≥47years of age appeared to be associated with the CPAP-emergent group. The results suggest that elderly patients with higher AHI at BPSG may present with CPAP-emergent PLMS.

Prevalence and clinical characteristics of restless legs syndrome in chronic kidney disease patients.

OBJECTIVE: To clarify the prevalence of restless legs syndrome (RLS) in the chronic kidney disease (CKD) population and determine the relationship between severity of renal dysfunction and risk of RLS as well as the impact of the disorder on mood and sleep disturbance, we conducted a questionnaire survey followed by face-to-face interviews with Japanese CKD patients. METHODS: We sent a questionnaire battery including demographics items, the National Institutes of Health/International RLS Study Group (IRLSSG) consensus questionnaire, the Center for Epidemiological Studies Depression Scale, and the Pittsburgh Sleep Quality Index to eligible CKD patients (n=514) and age- and sex-matched controls (n=535). Structured interviews were performed for the diagnosis of RLS. RESULTS: The prevalence of positive RLS in the CKD subjects was significantly higher than that in the controls (3.5% vs. 1.5%, p=0.029). The proportion of renal failure (RF) in CKD subjects with RLS was significantly higher than in those without RLS, and multiple logistic regression analysis revealed that the presence of RLS symptoms was associated only with the existence of RF. In addition, the presence of both RLS and CKD was significantly associated with the presence of depression and sleep disturbance. CONCLUSIONS: The risk of RLS in the CKD population was higher than that in the general population and increased with the progression of renal dysfunction. Additionally, the existence of RLS might play a role in an increased risk for developing depression and sleep disturbance in the CKD population.

Evening preference is related to the incidence of depressive states independent of sleep-wake conditions.

Although evening preference has recently been identified as a risk factor for depression, it has not been substantiated whether evening preference is a direct risk factor for depressive states, or if it is associated secondarily through other factors, such as delayed sleep timing and shortened sleep duration. The objective of this study is to investigate associations in Japanese adult subjects between evening preference and incidence of depressive states, adjusting for various sleep parameters related to depressive states. The Morningness-Eveningness Questionnaire (MEQ), the Pittsburgh Sleep Quality Index (PSQI), and the Center for Epidemiologic Studies Depression Scale (CES-D) were administered to 1170 individuals (493 males/677 females; mean and range 38.5 and 20-59 yrs) to assess their diurnal preferences, sleeping states, and presence of depression symptoms. Subjects were classified into five chronotypes based on MEQ scores. Evening preference was associated with delayed sleep timing, shortened sleep duration, deteriorated subjective sleep quality, and worsened daytime sleepiness. Logistic regression analysis demonstrated that the extreme evening type (odds ratio [OR] = 1.926, p = .018) was associated with increased incidence of depressive states and that the extreme morning type (OR = 0.342, p = .038) was associated with the decreased incidence of depressive states, independent of sleep parameters, such as nocturnal awakening (OR = 1.844, p < .001), subjective sleep quality (OR = 2.471, p < .001), and daytime sleepiness (OR = 1.895, p = .001). However, no significant associations were observed between the incidence of depressive states and sleep duration, sleep timing, and sleep debt (levels of insufficient sleep). Although the findings of this study do not demonstrate a causative relationship between evening preference and depression, they do suggest the presence of functional associations between mood adjustment and biological clock systems that regulate diurnal preference. They also suggest that evening preference might increase susceptibility to the induction of mood disorders.

Diurnal fluctuations in subjective sleep time in humans.

Humans have the ability to estimate the passage of time in the absence of external time cues. In this study, we subjected 22 healthy males (aged 21.8±1.9 years) to a 40-min nap trial followed by 80min of wakefulness repeated over 28h, and investigated the relationship between various sleep parameters and the discrepancy (ΔST) of time estimation ability (TEA) during sleep, defined by the difference between actual sleep time (ST) and subjective sleep time (sub-ST) in each nap interval. Both ST and sub-ST were significant diurnal fluctuations with the peak in the early morning (9h after dim-light melatonin onset time, 2h after nadir time of core body temperature rhythm), and subjective sleep duration was estimated to be longer than actual times in all nap intervals (sub-ST>ST). There were significant diurnal fluctuations in discrepancy (sub-ST-ST) of TEA during sleep, and the degree of discrepancy correlated positively with increase in the amount of REM sleep and decrease in the amount of slow-wave sleep. These findings suggest that human TEA operates at a certain level of discrepancy during sleep, and that this discrepancy might be related to the biological clock and its associated sleep architecture.

Non-pharmacological self-management of sleep among the Japanese general population.

STUDY OBJECTIVES: The present study was conducted to clarify the prevalence of non-pharmacological self-management (nPSM) practices for obtaining good sleep and to identify favorable nPSM practices that could be applied for reducing excessive daytime sleepiness (EDS). We analyzed epidemiological data for an authentic representative sample of the Japanese population. METHODS: Data obtained from 24,686 adults via a self-administered questionnaire completed in the Active Survey of Health and Welfare 2000 were used for analyses. The prevalence of individual nPSM practices was calculated by gender. Subsequently, the associations between such practices and EDS were examined using logistic regression analyses. RESULTS: "Having a bath" was the most prevalent nPSM practice for both men (59.0%) and women (64.4%), followed by "maintaining a regular schedule" (men: 49.0%, women: 58.6%), "reading or listening to music" (men: 43.4%, women: 49.4%), "snacking on food and/or beverages" (men: 36.1%, women: 27.9%), and "exercising" (men: 26.2%, women: 29.4%). The prevalence of "maintaining a regular schedule" increased with age. Multiple logistic regression analyses revealed that having a bath and maintaining a regular schedule had negative associations with EDS, whereas snacking on food and/or beverages had a positive association. CONCLUSIONS: Having a bath and maintaining a regular schedule were identified as favorable nPSM practices for reducing EDS, whereas snacking on food and/or beverages was considered to be an unfavorable nPSM practice.

Time estimation during sleep relates to the amount of slow wave sleep in humans.

Humans have the ability to estimate the amount of time that has elapsed during sleep (time estimation ability; TEA) that enables a subset of individuals to wake up at a predetermined time without referring to a watch or alarm clock. Although previous studies have indicated sleep structure as a key factor that might influence TEA during sleep, which sleep parameters could affect the TEA has not been clarified. We carried out an experimental study in which 20 healthy volunteers participated in six time estimation trials during the 9-h nighttime sleep (NS) experiment or daytime sleep (DS) experiment. The time estimation ratio (TER, ratio of the subjective estimated time interval to actual time interval) decreased significantly from the first to the sixth trial in both the NS and DS experiments. TER correlated positively with slow wave sleep (SWS) in both experiments, suggesting that SWS was a determining factor in accurate time estimation, irrespective of circadian phase they slept. No other sleep parameters showed steady influence on TEA. The present findings demonstrate that longer period of SWS is associated with the longer sleep time they subjectively experienced during sleep.