Acrophase Of Rhythm Research Articles

Circadian adaptation to night shift work is associated with higher REM sleep duration

ObjectiveTo investigate the influence of the degree of circadian adaptation to night work on sleep architecture following night shift. MethodsThirty four night workers (11 females; 33.8 ± 10.1years) completed a simulated night shift following 2-7 typical night shifts. Participants completed a laboratory-based simulated night shift (21:00-07:00 hours), followed by a recovery sleep opportunity (∼09:00-17:00 hours), recorded using polysomnography. Urinary 6-sulphatoxymelatonin (aMT6s) rhythm acrophase was used as a marker of circadian phase. Sleep duration and architecture were compared between individuals with aMT6s acrophase before (unadapted group, n = 22) or after (partially adapted group, n = 12) bedtime. ResultsBedtime occurred on average 2.16 hours before aMT6s acrophase in the partially adapted group and 3.91 hours after acrophase in the unadapted group. The partially adapted group had more sleep during the week before the simulated night than the unadapted group (6.47 ± 1.02 vs. 5.26 ± 1.48 hours, p = .02). After the simulated night shift, both groups had similar total sleep time (partially adapted: 6.68 ± 0.80 hours, unadapted: 6.63 ± 0.88 hours, p > .05). The partially adapted group had longer total rapid eye movement sleep duration than the unadapted group (106.79 ± 32.05 minutes vs. 77.90 ± 28.86 minutes, p = .01). After 5-hours, rapid eye movement sleep accumulation was higher in the partially adapted compared to the unadapted group (p = .02). Sleep latency and other stages were not affected by circadian adaptation. DiscussionPartial circadian adaptation to night shift was associated with longer rapid eye movement sleep duration during daytime sleep, highlighting the influence of entrainment between the sleep-wake cycle and the circadian pacemaker in night workers. The findings have important implications for sleep and subsequent alertness associated with shift work.

Colorectal bradyarrhythmia syndrome as risk factor for constipation and colorectal cancer

Purpose. To prove that colorectal bradyarrhythmia syndrome is a precursor and predictor of constipation and colorectal cancer.Materials and methods. Using the non-invasive method of chronoenterography – weekly monitoring of the circadian rhythm of the enteral evacuation function, 2869 people who consider themselves relatively healthy were examined. The test ‘Rhythms and Health’ was used to identify the frequency and acrophase of the rhythm of defecation, as well as to assess the level of quality of life. We compared the occurrence of morning acrophase of the bowel rhythm in individuals with a regular bowel rhythm (at least 7 times a week) and in individuals with irregular (delayed) bowel function (with a stool frequency of 1–2 to 5–6 times a week). Three stages of colorectal bradyarrhythmia syndrome severity were analyzed: mild, moderate, and severe. The main symptoms of colorectal bradyarrhythmia syndrome were identified. The risk of colorectal cancer in patients with constipation was analyzed according to known data.The results of the study. It is shown that the earliest stages of enteral evacuation function irregularity (mild – 5–6, and moderate – 3 times a week 4 times a week) occur almost 10 times more often than the severe stage (1–2 times a week) of colorectal bradyarrhythmia syndrome in the form of constipation. A regular dependence of the regularity of the defecation rhythm on the position of the acrophase of this rhythm in the daily cycle was established: the regular rhythm of defecation (7 times a week) is associated with the presence of morning acrophase of the stool rhythm, and colorectal bradyarrhythmia (1–6 times a week) is associated with the absence of morning acrophase of the defecation rhythm. A natural relationship between a decrease in the frequency of defecation and a decrease in the level of quality of life was revealed. It is proved that the rarer the frequency of stool, the higher the tendency to take laxatives.Conclusions. Colorectal bradyarrhythmia syndrome occurs in both young people aged about 20 years and adults, and is almost 10 times more common than constipation. Constipation is a proven risk factor for colorectal cancer, as it increases this risk by 2–4 times. A high level of quality of life is characteristic of individuals with a regular stool rhythm, and colorectal bradyarrhythmia syndrome is characterized by a decrease in the level of quality of life in accordance with the aggravation of the stage of this syndrome.

The 24-hour rhythm in alcohol craving and individual differences in sleep characteristics and alcohol use frequency.

Evidence implicates sleep/circadian factors in alcohol use, suggesting the existence of a 24-h rhythm in alcohol craving, which may vary by individual differences in sleep factors and alcohol use frequency. This study sought to (1) replicate prior findings of a 24-h rhythm in alcohol craving, and (2) examine whether individual differences in sleep timing, sleep duration, or alcohol use frequency are related to differences in the timing of the peak of the craving rhythm (i.e., the acrophase) or magnitude of fluctuation of the rhythm (i.e., amplitude). Finally, whether such associations varied by sex or racial identity was explored. Two-hundred fifteen adult drinkers (21 to 35years of age, 72% male, 66% self-identified as White) completed a baseline assessment of alcohol use frequency and then smartphone reports of alcohol craving intensity six times a day across 10days. Sleep timing was also recorded each morning of the 10-day period. Multilevel cosinor analysis was used to test the presence of a 24-h rhythm and to estimate acrophase and amplitude. Multilevel cosinor analysis revealed a 24-h rhythm in alcohol craving. Individual differences in sleep timing or sleep duration did not predict rhythm acrophase or amplitude. However, alcohol use frequency moderated this rhythm wherein individuals who used alcohol more frequently in the 30days prior to beginning the study had higher mean levels of craving and greater rhythm amplitudes (i.e., greater rhythmic fluctuations). Associations did not vary by sex or racial identity. Results show that alcohol craving exhibits a systematic rhythm over the course of the 24h and that the frequency of alcohol use may be relevant to the shape of this rhythm. Consideration of daily rhythms in alcohol craving may further our understanding of the mechanisms that drive alcohol use.

Aging disrupts the temporal organization of antioxidant defenses in theheart of male ratsand phase shifts circadian rhythms of systolic blood pressure.

Aging is one of the main risk factors for cardiovascular diseases, and oxidative stress is a key element responsible for the development of age-related pathologies. In addition, the alteration of circadian rhythms also contributes to cardiovascular pathology, but the underlying mechanisms are not well defined. We investigated the aging consequences on the temporal patterns of antioxidant defenses, the molecular clock machinery, and the blood pressure, in the heart of male rats maintained under constant darkness (free running) conditions. Male Holtzman rats from young adult (3-month-old) and older (22-month-old) groups were maintained under constant darkness (12-h dark:12-h dark, DD) condition during fifteen days before the experiment. After the DD period, heart ventricle samples were isolated every 4-h throughout a 24-h period. We observed circadian rhythms of catalase (CAT) and glutathione peroxidase (GPx) mRNA expression, as well as ultradian rhythms of Nrf2 mRNA levels, in the heart of young adult rats. We also found circadian oscillations of CAT and GPx enzymatic activities, reduced glutathione (GSH) and BMAL1 protein in the same group. Interestingly, aging abolished the rhythms of CAT and GPx enzymatic activities, phase-shifted the rhythm's acrophases of GSH and BMAL1 protein levels and turned circadian the ultradian oscillation of Nrf2 expression. Moreover, aging phase-shifted the circadian pattern of systolic blood pressure. In conclusion, aging modifies the temporal organization of antioxidant defenses and blood pressure, probably, as a consequence of a disruption in the circadian rhythm of the clock's transcriptional regulator, BMAL1, in heart.

746 Delayed Rhythm Is Associated with Enhanced Discrimination for Negative Emotional Information

Abstract Introduction Mnemonic discrimination, the ability to differentiate novel and highly similar but not identical stimuli, is negatively associated with sleep deprivation and depression. Depression is additionally associated with increased discrimination specifically for negative emotional stimuli. While sleep and circadian activity rhythm (CAR) disturbances are common in depression and have been reported to have negative impact on hippocampal-dependent memories, their relationship with emotional discrimination has yet to be investigated. Methods As part of a larger study, 14 patients with DSM-5 major depressive disorder (22.9±4.1 years, 71.4% female) and 13 healthy controls (29.4±8.5 years, 61.5% female) were evaluated with wrist-actigraphy (7–14 days) and completed an emotional discrimination task. Lure discrimination index (LDI) for each emotion type (i.e., negative, neutral, and positive) was calculated to indicate how well participants discriminated among highly similar lures. Actigraphy-derived sleep parameters included total sleep time (TST), sleep efficiency (SE), and midsleep time. Minute-by-minute actigraphy-derived activity counts were used to characterize CAR and parametrized using cosinor analysis and Generalized Additive Models (GAM) deriving the rhythm Acrophase, Amplitude, UP time, and DOWN time. A repeated measures ANOVA (within-subjects: emotion, between-subjects: group) assessed whether mnemonic discrimination differed between patients with MDD and controls. Partial correlations examined the association between sleep and CAR parameters with mnemonic discrimination, while controlling for age, state anxiety, depression severity, TST, and groups. Results We found a significant effect of emotion [F(2,90)=3.25, p=0.043], where neutral information was remembered better than emotional information (p’s<0.005); no significant effect of group (MDD vs. control) was observed. Midsleep time and Acrophase were each positively associated with negative LDI (r=0.576, p=0.008; r=0.540, p=0.014, respectively). Exploratory GAM results suggested a significant positive correlation between UP time and negative LDI (r=0.497, p=0.022). TST, SE, Amplitude or DOWN time was not associated with LDIs. Conclusion Delayed CAR, characterized by latter midsleep time and delayed acrophase and peak time of the morning activity, is associated with increased discrimination for negative emotional information, independent of depressive symptom severity. Future studies are needed to replicate these findings and further explore the potential cognitive benefits of adjunctive interventions addressing sleep/CAR in mitigating symptoms of depression. Support (if any) National Institutes of Health R01 432MH102392.

ВЛИЯНИЕ РИТМОВ ГИДРОМЕТЕОРОЛОГИЧЕСКИХ ПОКАЗАТЕЛЕЙ НА ВОДНО-МИНЕРАЛЬНЫЙ ГОМЕОСТАЗ ПРИ ГИПЕРТОНИЧЕСКОЙ БОЛЕЗНИ

70 practically healthy subjects and 100 patients with hypertensive disease were united regimen of diet, sleep and wakefulness. Urine was collected with 4-hour portions during 3-5 days. Each specimen was analyzed for electrolytes (sodium, potassium, phosphorus, chlorine, calcium, magnesium) and trace elements (iron, copper, zinc, chromium, cadmium, vanadium). Rhythms parameters have been estimated by dispersion analysis for nonsinusoidal rhythms and by nonlinear least squares method for sinusoidal rhythms. In healthy subjects in 91% cases of 593 rhythmological investigations urinary excretion electrolytes and trace elements statistically significant rhythms were observed. Healthy subjects characterized with circadian rhythms and with definite value of mesor and amplitude within the confidence limit. Acrophases of rhythms were mostly individual. The data witness that in early stage of HD electrolytes and trace elements exeretion rhythms 22% were statistically nonsignificant. Among significant rhythms of electrolytes and trace elements excretion infradians prevail - 46%. Statistically significant rhythms of electrolytes and trace elements excretion were not revealed in most of patients in the late stage of HD. Among significant rhythms circadian prevail - 48%. The data witness that in HD the coefficient of correlation between the biorhythms and the rhythms of hydrometerological indices were statistically nonsignificant (for early stage - 37% and for late stage - 30%).

Endogenous Circadian Regulation of Female Reproductive Hormones.

Studies suggest that female reproductive hormones are under circadian regulation, although methodological differences have led to inconsistent findings. To determine whether circulating levels of reproductive hormones exhibit circadian rhythms. Blood samples were collected across ∼90 consecutive hours, including 2 baseline days under a standard sleep-wake schedule and ∼50 hours of extended wake under constant routine (CR) conditions. Intensive Physiological Monitoring Unit, Brigham and Women's Hospital. Seventeen healthy premenopausal women (22.8 ± 2.6 years; nine follicular; eight luteal). Fifty-hour CR. Plasma estradiol (E2), progesterone (P4), LH, FSH, SHBG, melatonin, and core body temperature. All hormones exhibited significant 24-hour rhythms under both standard sleep-wake and CR conditions during the follicular phase (P < 0.05). In contrast, only FSH and SHBG were significantly rhythmic during the luteal phase. Rhythm acrophases and amplitudes were similar between standard sleep-wake and CR conditions. The acrophase occurred in the morning for P4; in the afternoon for FSH, LH, and SHBG; and during the night for E2. Our results confirm previous reports of ∼24-hour rhythms in many female reproductive hormones in humans under ambulatory conditions but demonstrate that these hormones are under endogenous circadian regulation, defined as persisting in the absence of external time cues. These results may have important implications for the effects of circadian disruption on reproductive function.

Seasonal differences in rhythmicity of salivary cortisol in healthy adults.

The existence of seasonal changes in secretion of stress hormones and inflammatory mediators by humans is not certain. Here, we aimed to determine whether concentrations of cortisol and IL-6 displayed seasonal rhythmicity. The study was performed in Poznań, Poland (52°N, 16°E) in 7 healthy female volunteers (age 22.6 ± 0.8 yr). Samples of whole mixed unstimulated saliva were collected in winter (February) and summer (June) at 2-h intervals over a 24-h period and analyzed for cortisol and IL-6 by immunoassays. During each season, the subjects answered questionnaires related to their sleeping habits, food intake, physical activity, and perceived seasonality. It turned out that salivary concentrations of cortisol followed a daily rhythm both in winter and summer, as determined by a cosine analysis. However, compared with the winter season, a midline-estimating statistic of rhythm in the summer was significantly higher. Moreover, the rhythm acrophase occurred ~4 h later in the summer than in the winter, whereas the amplitudes did not differ. These fluctuations did not correspond to sleeping habits, food and fluid intake, physical exercise, and the self-assessed chronotype. However, the individuals with higher scores on the seasonal affective disorder scale showed a tendency toward lower relative cortisol amplitude in the summer. In contrast to cortisol, salivary IL-6 concentration did not display daily rhythmicity, and its concentrations did not differ significantly between the seasons. In conclusion, in the summer, cortisol level in saliva is elevated, and its circadian pattern of secretion is shifted. The causes for these alterations do not seem to be related to lifestyle and thus remain to be established.

The benefits of primary prevention of colorectal cancer around the age of 20 compared to secondary prevention after the age of 50

The major advantages of primary prevention of colorectal cancer in young adults (around 20 years) compared with se condary prevention in adults (after 50 years). Primary prevention is aimed at screening and eliminating one of the major proven risk factors for colon cancer – chronic constipation and its predecessor – colorectal bradyarrhythmia – as slower circadian rhythm of defecation. The main advantages of primary prevention of colorectal cancer are: non-invasiveness, safety, efficiency and timeliness. Screening of colorectal bradyarrhythmia at 2501 operating physician is allowed to diagnose this arrhythmia in 44% of the surveyed entities. There is discovered the new fundamental dependence between the regularity of circadian rhythm of defecation and an acrophase of this rhythm. The implementation of the morning acrophase of the circadian rhythm of defecation is the key mechanism of the regularity of this rhythm. Repeated screening of colorectal bradyarrhythmia in individuals around the age of 20 years (a month after informing students about the law of circadian rhythm in the brain and intestine) showed that 53% of the students began to observe the morning routine of bowel movements. This led to a transition of moderate stage of colorectal bradyarrhythmia severity (3-4 times a week) in an easy stage (5-6 times a week). It’s proved the possibility of primary (behavioral) prevention of colorectal bradyarrhythmia (colorectal coprostasis) as a risk factor for colorectal cancer. Secondary prevention of colon cancer is associated with the invasiveness of colonoscopy, its possible complications (bleeding, perforation of bowel and fatal outcomes), the high cost of special equipment and late in the approach to screening for colorectal cancer (after the appearance of blood in the stool or after 50 years).

Daily levels and rhythm in circulating corticosterone and insulin are altered with photostimulated seasonal states in night-migratory blackheaded buntings

The circadian rhythms are involved in the photostimulation of seasonal responses in migratory blackheaded buntings. Here, we investigated whether changes in daily levels and rhythm in corticosterone (cort) and insulin secretions were associated with transitions in the photoperiodic seasonal states. Buntings were exposed to short days to maintain the winter (photosensitive) non-migratory state, and to long days for varying durations to induce the premigratory, migratory (shown by migratory restlessness at night, Zugunruhe) and summer non-migratory (photorefractory) states. We monitored activity patterns, and measured plasma cort and insulin levels at six and four times, respectively, over 24h in each seasonal state. Buntings were fattened and weighed heavier, and exhibited intense nighttime activity in the migratory state. The daytime activity patterns also showed seasonal differences, with a bimodal pattern with morning and evening activity bouts only in the summer non-migratory state. Further, the average baseline hormone levels were significantly higher in premigratory and migratory than in the winter non-migratory state. Both cort and insulin levels showed a significant daily rhythm, but with seasonal differences. Whereas, cort rhythm acrophases (estimated time of peak secretion over 24h) were at night in the winter non-migratory, premigratory and migratory states, the insulin rhythm acrophases were found early in the day and night in winter and summer non-migratory states, respectively. These results suggest that changes in daily levels and rhythm in cort and insulin mediate changes in the physiology and behavior with photostimulated transition in seasonal states in migratory blackheaded buntings.

NF-κB signalling is involved in immune-modulation, but not basal functioning, of the mouse suprachiasmatic circadian clock.

Circadian rhythms are recurring near-24 hour patterns driven by an endogenous circadian timekeeping system. The master pacemaker in this system is the hypothalamic suprachiasmatic nucleus (SCN). Recently interest has been drawn to how the SCN clock responds to immune system stimulation. A major signalling component in the immune system is nuclear factor (NF)-κB. In the present study we examined the role of NF-κB in SCN function. Whilst serum shocked fibroblasts showed rhythmic nuclear localisation of p65 and p65-dependent transcription, there were no circadian changes in the SCN in expression of the NF-κB components p65, c-Rel, p-IκB or p-IKK. Chronic treatment with the NF-κB inhibitor PDTC did not impact on circadian or diurnal rhythms. Phase-shifting light pulses did not impact on SCN expression of p65, and PDTC treatment did not attenuate the behavioural or molecular response to light pulses. Peripheral treatment with lipopolysaccharide resulted in increased NF-κB component expression in the SCN. In vitro experiments with SCN slice cultures showed that treatment with NF-κB inhibitors did not markedly alter rhythmic changes in PER2::LUC expression. Further, SCN slices from nf-κb::luc mice did not show any evidence for circadian rhythms in NF-κB-mediated transcription. Experiments utilising older mice (~16months old) showed that SCN treatment invitro with PDTC resulted in increased amplitude of rhythmic PER2::LUC expression, and LPS treatment resulted in altered PER2::LUC rhythm acrophase. Overall, we interpret our results as providing evidence for the involvement of NF-κB in the suprachiasmatic circadian clock following immune stimulation, but not under basal conditions.

Monitoring of total locomotor activity in mares during the prepartum and postpartum period

The aim of this study was to investigate the daily rhythms of total locomotor activity (TLA) in mares during the prepartum and postpartum periods and the existence of these rhythms at the time of birth in neonatal foals. For this purpose, TLA was recorded in 9 mares starting from the third day preceding the date of foaling until 3 days after foaling. The TLA was recorded in the newborn foals starting from 2 to 6 hours after birth until the third day of life. Animals were housed in individual straw-bedded boxes (4.0 × 3.5 m) under natural photoperiod and ambient temperature. Animals were fed twice a day (7 am; 5 pm) and were allowed to go to the paddock during the day (from 10 am to 4 pm). Mares showed a diurnal activity, and the total amount of daily activity statistically changed during the 6 days of monitoring. Activity was statistically higher in the prepartum period than in the postpartum period. In foals, a statistical increase of the total amount of daily activity was observed in the 3 days of monitoring, but no differences were observed in the amount of activity recorded during the photophase and the scotophase. Both in mares and foals, rhythmicity was observed on the second and second days postpartum, and the acrophase of rhythm did not change during the monitored period. The mean level and amplitude of rhythm were higher in foals than in mares. In mares, the amplitude was lower during day 3 postpartum compared to days 1 and 2 prepartum. Robustness of rhythm in mares was lower in day 3 postpartum compared to days 1 and 3 prepartum. In conclusion, although TLA significantly changed from the 3 days prepartum to the 3 days postpartum, the acrophase of rhythm was the same in all experimental conditions and was opposite to that observed in foals.

Reliability and validity of the Korean version of Morningness–Eveningness Questionnaire in adults aged 20–39 years

Morningness–Eveningness (ME) can be defined by the difference in individual diurnal preference observed from general behavioral patterns including sleep habits. The Horne & Östberg Morningness–Eveningness Questionnaire (MEQ) has been used for classifying ME types. We examined the reliability of a Korean version of the MEQ (Korean MEQ) and verified its validity by comparing responses on the Korean MEQ to objectively-recorded sleep–wake rhythms. After translating and back translating the MEQ from English into Korean, we examined the internal consistency of 19 items of the Korean MEQ in 91 subjects, and the test–retest reliability in 21 subjects who took the Korean MEQ twice, 4 weeks apart. The Korean MEQ was then administered to 1022 young adult subjects. A subset of 46 morning, neither, and evening type subjects took part in a validation study in which their rest-activity timing was collected by actigraphy for 7 days. Cosinor analyses on these data were done to obtain the acrophase and amplitude of the sleep–wake rhythm. Cronbach’s alpha of the total scores from the Korean MEQ was 0.77, and the test–retest reliability intra-class correlation coefficient was 0.90 (p < 0.0001). There was a significant negative correlation between Korean MEQ score and reported sleep–wake timing among the entire cohort (p < 0.0001). There was a significant difference in bedtime and wake time (on both work and free days), and in the mean sleep–wake rhythm acrophase, between ME types (p < 0.01). In this study, the validity of the Korean MEQ was verified by illustrating the difference in acrophases of the sleep–wake rhythm between the ME types in young adults.

Optimized light therapy for non-seasonal major depressive disorder: Effects of timing and season

Light Therapy (LT) when combined with standard antidepressant treatment for unipolar depression hastens recovery. We studied the influence of LT timing on the antidepressant efficacy of LT and the influence of the season of treatment and recurrence on the response to treatment. We studied 70 inpatients affected by Unipolar Depression, treated for three weeks with combined LT and venlafaxine. Two-third of the patients received LT following a predictive algorithm based on MEQ scores; the others received LT at 11:00 a.m. Severity of depression was rated on the Hamilton Depression Rating Scale (HDRS). A subgroup of patients wore activity monitors. HDRS scores significantly decreased during treatment (Friedman's ANOVA: χ2=186.82, p<0.00001). LT administered in the early morning showed a better relative efficacy than late morning (F=4.576; p=0.012) with the clinical improvement correlating with an advance in rest-activity rhythm acrophase (r=-0.336; p=0.017). Season of hospitalization interacted with LT timing and time in influencing response to treatment (F=3.101; p=0.049) and season of episode recurrence significantly interacted with LT timing, season of hospitalization and time (F=5.925; p=0.0035). The major limitation of the study is the small sample size when considering simultaneously LT schedules, season of treatment and recurrence. Moreover, even if none of the patients fulfilled DSM-IV criteria for seasonal pattern of recurrence, they were not administered any questionnaire about seasonality. We confirmed the usefulness of LT as a non-pharmacological antidepressant therapy for non-seasonal depression. Season and timing of administration and timing of the rest-activity cycle affected response to treatment.

Circadian concentrations of free testosterone, selected markers of bone metabolism, osteoprotegerin and its ligand sRANKL in obese postmenopausal women

It has been suggested that increased testosterone secretion in postmenopausal obese women might have some protective effect on bone tissue; the association might be significantly influenced by the RANKL/RANK/OPG system. The aim of the study was to determine whether postmenopausal obese women showed any relationship between the pattern of adipose tissue distribution, circadian free testosterone (FT) concentrations and bone metabolism (as assessed based on circadian osteocalcin [OC] and C-terminal telopeptide [CTx] levels), and to establish whether osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) might play a role in the relationship. FT, OC, CTx, OPG and soluble RANKL (sRANKL) levels were determined by ELISA in serum samples collected every three hours for 24 hours from 47 postmenopausal women (12 with gynoid obesity [GO], 17 with android obesity [AO], and 18 healthy individuals). Obese women demonstrated an adipose tissue distribution-dependent increase in mean circadian FT levels and a decrease in mean circadian OC, CTx, OPG and sRANKL compared to control participants. In GO subjects, these changes were accompanied by smaller FT amplitudes, suppression of the circadian rhythms of bone markers and OPG, and a shift of sRANKL rhythm acrophase, whereas AO subjects showed a decrease in bone marker amplitudes and suppression of OPG and sRANKL rhythms. In comparison with the controls, significant adipose tissue distribution-dependent changes were found in the correlations between FT and bone markers, FT and OPG, OC and CTx, OPG and sRANKL, CTx and OPG, and CTx and sRANKL. Compared to GO participants, those with AO had higher coefficients of correlations between mean circadian FT and OC as well as between OC and CTx, and lower in the case of FT and sRANKL as well as CTx and OPG and CTx and sRANKL. Postmenopausal obesity results in adipose tissue distribution-dependent alterations in circadian FT levels accompanied by suppression of bone metabolism and a decline in circadian variations of the osteokines under investigation, especially sRANKL. Increased FT secretion in postmenopausal women might exert a protective effect on bone tissue, most likely via a shift in the OPG/RANKL ratio that tilts the balance toward a functional excess of OPG.

Time Of Habitual Training Does Not Alter Circadian Rhythm Of Swim Performance

Some studies have found better athletic performance at the usual time of training relative to other times of day. These results could reflect either a change in the circadian system or a non-circadian adaptation that results in better performance at the accustomed time of training. However, other studies have provided equivocal or negative results. PURPOSE: To examine whether the circadian rhythm of swim performance differs between individuals who habitually train at a certain time(s) of day compared to those who do not. METHODS: 25 swimmers were assessed for 50-55 consecutive hr in the laboratory while adhering to a 3-hr ultra-short sleep/wake cycle, a common chronobiological technique. Swimmers performed 6 maximal 200-m swims, with each trial separated by 9 hr. Performances were z-transformed and expressed relative to time of day. The time of habitual training for each swimmer was obtained via questionnaire prior to the study. Estimates of swim performance rhythm amplitude (i.e., range of performance), acrophase (i.e., time of peak performance), and mesor (i.e., fitted mean value) were obtained via cosinor analysis and compared between groups with independent sample t-tests. Group data were analyzed via ANCOVA with trial number as a covariate and time of day and habitual training time as fixed factors. RESULTS: Approximately ½ of the swimmers (n=12) reported no usual time of training. The half (n=13) who had habitual swim times trained daily between 0600-0900 hr, 1600-1800 hr, or at both of these times of day. Those who reported a habitual time of training had lower mesors (i.e., faster swim time; p<0.001), but did not have different performance rhythm acrophases or amplitudes compared to those without a specific time of training (n=12). No group differences were found in swim performance when analyzed via ANCOVA. CONCLUSIONS: This study found minimal evidence of different swim performance rhythm characteristics between those who habitually trained at a particular time of day versus those who did not. No evidence was found for superior performance that was specific to the usual time of training. However, the data do not discount the possibility that such an advantage might be observed under usual diurnal conditions, due to variations in diet, sleep, rest, and performance preparation.

Blunting of Circadian Rhythms and Increased Acrophase Variability in Sleep‐Time Hypertensive Subjects

24 h and ultradian rhythms of blood pressure (BP) have been previously shown to be disorganized in nocturnal hypertensive subjects. The present study was undertaken to further analyze the ultradian and circadian BP rhythm structure in sleep‐time hypertensive subjects with normal or elevated awake‐time BP levels. Fourier analysis was used to fit 24, 12, 8, and 6 h curves to mean BP as well as heart rate (HR) time series data derived from 24 h ambulatory blood pressure monitoring. Awake and sleep periods were defined according to individual sleep diaries. Awake‐time hypertension was defined as diurnal systolic (SBP) and/or diastolic BP (DBP) means ≥135/85 mmHg. Sleep‐time hypertension was defined as nocturnal SBP and/or DBP means ≥120/70 mmHg. The sample included 240 awake‐time normotensive subjects (180 sleep‐time normotensives and 60 sleep‐time hypertensives) and 138 untreated awake‐time hypertensive subjects (31 sleep‐time normotensives and 107 sleep‐time hypertensives). The amplitude and integrity (i.e., percent rhythm) of the 24 and 12 h BP rhythms were lower in the sleep‐time hypertensive subjects and higher in the awake‐time hypertensive subjects. However, no differences were detected when the integrity and amplitude of the 6 and 8 h mean BP rhythms were analyzed. The sleep‐time hypertensive group showed significantly higher 24 h BP rhythm acrophase variability. No differences could be found in any of the HR rhythm parameters. Altogether, the findings suggest a disorganization of the BP circadian rhythm in sleep‐time hypertensives that results in reduced 24 h rhythm amplitude and integrity that could be related to cardiovascular risk.

A Multicomponent Nonpharmacological Intervention Improves Activity Rhythms Among Nursing Home Residents With Disrupted Sleep/Wake Patterns

Sleep and circadian rhythms are disrupted among many nursing home (NH) residents. We examined the impact of a multicomponent nonpharmacological intervention on 24-hour rest/activity rhythms among long-stay NH residents. The study was a randomized controlled trial in which, following a 3-day baseline, participants received 5 days of either usual care (control condition) or the active intervention. The intervention combined increased exposure to outdoor bright light, efforts to keep residents out of bed during the day, structured physical activity, institution of a bedtime routine, and efforts to reduce nighttime noise and light in residents' rooms. For 100 residents with baseline and follow-up wrist actigraphy data (mean age = 87 years; 76% women), rest/activity rhythms were modeled to determine the rhythm acrophase (peak time), nadir (trough time), midline estimating statistic of rhythm (MESOR) (midpoint), amplitude (height of peak), slope, and the rest period/active period ratio (alpha). The intervention led to an increase in the duration of the "active" portion of the rhythm, which was primarily accounted for by a shift in the rest/activity rhythm rise to an earlier time. Findings persisted when analyses were adjusted for age, cognitive functioning, medical comorbidities, and behavioral disturbances. These findings suggest that the intervention may effectively improve the robustness of rest/activity rhythms in NH residents. Further research is needed to examine the impact of similar interventions on other measures of circadian rhythms (e.g., body temperature, melatonin) among NH residents.

Daytime Sleeping, Sleep Disturbance, and Circadian Rhythms in the Nursing Home

This study reports the frequency of abnormal daytime sleeping and identifies factors related to daytime sleeping, nighttime sleep disturbance, and circadian rhythm abnormalities among nursing home residents. The authors conducted secondary analysis of data collected under usual care conditions within a nonpharmacologic sleep intervention trial. All residents from four Los Angeles nursing homes were screened for daytime sleeping (asleep>or=15% of observations, 9:00 am-5:00 pm). Consenting residents with daytime sleeping had two nights of wrist actigraphy to assess nighttime sleep disturbance (asleep<80%, 10:00 pm-6:00 am). Residents with nighttime sleep disturbance completed an additional 72-hour wrist actigraphy recording to assess circadian activity rhythms and light exposure. Sixty-nine percent of 492 observed residents had daytime sleeping, of whom 60% also had disturbed nighttime sleep. Sleep disturbance and daytime sleeping were rarely documented in medical records. Residents spent one-third of the day in their rooms, typically in bed, and were seldom outdoors or exposed to bright light. More time in bed and less social activity were significant predictors of daytime sleepiness. Ninety-seven percent of residents assessed had abnormal circadian rhythms. More daytime sleeping and less nighttime sleep were associated with weaker circadian activity rhythms. Later circadian rhythm acrophase (peak) was associated with more bright light exposure. Daytime sleepiness, nighttime sleep disturbance, and abnormal circadian rhythms were common in nursing home residents. Modifiable factors (e.g., time in bed) are associated with sleep/wake abnormalities. Mental health specialists should consider the complexity of factors causing sleep problems in nursing home residents.

Effect of timed bright light treatment for rest-activity disruption in institutionalized patients with Alzheimer's disease

Disturbances in rest-activity rhythm are prominent and disabling symptoms in Alzheimer's disease (AD). Nighttime sleep is severely fragmented and daytime activity is disrupted by multiple napping episodes. In most institutional environments, light levels are very low and may not be sufficient to entrain the circadian clock to the 24-hour day. The purpose of this randomized clinical trial was to test the effectiveness of timed bright light therapy in reducing rest-activity (circadian) disruption in institutionalized patients with AD. The experimental groups received either morning (9.30-10.30 am) or afternoon (3.30-4.30 pm) bright light exposure ( > or = 2500 lux in gaze direction) Monday through Friday for 10 weeks. The control group received usual indoor light (150-200 lux). Nighttime sleep, daytime wake, and rest-activity parameters were determined by actigraphy. Repeated measures analysis of variance was employed to test the primary study hypotheses. Seventy institutionalized subjects with AD (mean age 84) completed the study. No significant differences in actigraphy-based measures of nighttime sleep or daytime wake were found between groups. Subjects in either experimental light condition evidenced a significantly (p < 0.01) more stable rest-activity rhythm acrophase over the 10-week treatment period compared to the control subjects whose rhythm phase delayed by over two hours. One hour of bright light, administered to subjects with AD either in the morning or afternoon, did not improve nighttime sleep or daytime wake compared to a control group of similar subjects. However, exposure to one-hour of bright light in either the morning or afternoon may provide sufficient additional input to the circadian pacemaker to facilitate entrainment to the 24-hour day.