Showing papers on "Morning published in 1995"

Correlation between volatile sulphur compounds and certain oral health measurements in the general population.

Abstract: Oral malodor was measured using a portable sulphide monitor in 2,672 individuals aged 18 to 64 years. In addition, dental (DMFT) and periodontal conditions (CPITN and attachment loss), dental plaque, and tongue coating status were assessed. Before clinical examination, subjects were interviewed about their oral health habits, smoking habits, and medical history. Data on volatile sulphur compounds (VSC) were analyzed by gender, age group, and time of measurement. There were no significant differences observed in the VSC between males and females in any age group. In each age group, the measured values of oral malodor were highest in the late morning group (58.6 ppb in average), followed by the late afternoon group (52.1 ppb), while lowest values were shown in the early afternoon group (39.4 ppb). Significant correlation was observed only between the VSC value and periodontal conditions and tongue coating status. The results also suggest that oral malodor might be caused mainly by tongue coating in the youn...

Cortisol in Saliva - Reference Ranges and Relation to Cortisol in Serum

Abstract: The aim of this study was to establish morning and evening reference ranges for cortisol in saliva. Another objective was to compare the concentrations of the mainly free cortisol in saliva to thos ...

Budesonide treatment of moderate and severe asthma in children: A dose-response study

Abstract: Objective: The purpose of the study was to evaluate the dose-response relationships of the inhaled corticosteroid budesonide in a double blind crossover study in 19 children with moderate and severe asthma. Methods: A 2-week placebo treatment period (run-in) was followed by three 4-week treatment periods during which 100, 200, and 400 μg of budesonide were given per day in randomized order. Urinary cortisol excretion, lung functions, and provection against exercise-induced asthma were assessed at the end of run-in and each treatment period. Furthermore, morning and evening peak expiratory flow rates, day and night symptoms, and use of rescue β 2 -agonists were recorded throughout the study. Results: One hundred micrograms of budesonide per day markedly improved symptoms, morning and evening peak expiratory flow rates, and use of rescue β 2 -agonists ( p p p Conclusions: Low doses of budesonide, which are not associated with any systemic side effects, have a marked antiasthma effect in children. Protection against exercise-induced asthma requires higher doses than achievement of symptom control. (J ALLERGY CLIN IMMUNOL 1995;95:29-33.)

Great Tit fat reserves: effects of changing and unpredictable feeding day length

Abstract: In two experiments, we tested the hypothesis that Great Tits (Parus major) adjust their fat reserves in response to feeding conditions. Experiment 1 tested the effect of a change in mean time at which food became available in the morning. Experiment 2 tested the effect of unpredictability in the onset of feeding time. In experiment 1, Great Tits increased their morning mass after the start of feeding was delayed by 3 h and decreased their mass when original conditions were restored. The response to shortened feeding day was more rapid than the response to lengthened day. On shortened feeding days, birds gained mass while eating less, suggesting that they reduced their expenditures. In experiment 2, birds gained more mass per day during the unpredictable than during the constant treatment. The performance of individuals was correlated across the two experiments, suggesting that the birds reacted to the mean and unpredictability in feeding conditions using the same mechanism. This mechanism might involve a more rapid response to worsening than to improving conditions.

Circadian Variation in the Efficacy of Tissue-Type Plasminogen Activator

Abstract: Background The frequency of onset of acute myocardial infarction follows a circadian pattern, with a peak incidence between 6:00 am and noon. Circadian variations have been defined for platelet aggregation, plasminogen-activator inhibitor, and a number of hemostatic and physiological factors, all of which might predispose toward clotting in the late morning and thrombolysis in the evening. Thus, the hypothesis for this retrospective analysis was that tissue-type plasminogen activator (TPA) has greater efficacy when administered between noon and midnight, as measured by coronary patency 90 minutes after initiation of treatment. Methods and Results Seven hundred twenty-eight patients were enrolled in either of two studies in which TPA was administered under a uniform protocol for the treatment of acute myocardial infarction. Of these, 692 patients had qualifying arteriograms that allowed standardized assessment by a core angiographic laboratory of the primary end point of 90-minute patency. TPA has a circadian pattern of efficacy, with greater TIMI grade 3 patency when administered between noon and midnight ( P P =.055) toward the greatest magnitude difference occurring between am and pm patency. The onset of myocardial infarction was confirmed to have a marked circadian variation with a peak incidence about 10:00 am. The peak efficacy of TPA was about 8:00 pm, representing a phase difference of about 10 hours after peak infarction incidence. Conclusions There is a circadian variation in the ability of TPA to rapidly open coronary arteries, with highest efficacy between noon and midnight. This complements clinical and in vitro knowledge of increased morning thrombosis and is concordant with knowledge of a fibrinolytic profile that is more favorable for evening lysis. This finding has implications for understanding the circadian pathophysiology of myocardial infarction and for its chronotherapy.

Salmeterol xinafoate in children on high dose inhaled steroids.

Abstract: BACKGROUND Current UK and international guidelines on asthma management recommend that, in pediatric patients still symptomatic on treatment with high-dose inhaled corticosteroids, consideration should be given to the introduction of regular twice daily long-acting beta 2-agonists. OBJECTIVE The purpose of this study was to assess the efficacy and safety of inhaled salmeterol xinafoate 50 micrograms bid via the Diskhaler when added to the existing treatment of children with moderate to severe asthma. METHODS A 12-week multicenter, double-blind, placebo-controlled, parallel group study was conducted at 78 hospital centers throughout the United Kingdom, involving 210 asthmatic children aged between 4 and 16 years of age. Morning peak expiratory flow (PEF), evening PEF, night-time and daytime symptoms and relief medication usage were recorded daily by the patient or parent over a 12-week treatment period. RESULTS Compared with placebo, the addition of salmeterol xinafoate to existing high dose inhaled corticosteroid treatment significantly improved mean morning PEF expressed as percent predicted (PEF-PP) during the first 4 weeks of treatment (median increase 6.5 percentage points P < .001). This effect persisted throughout the 12-week treatment period (P < .05). Both groups demonstrated an overall improvement in mean morning PEF-PP, 7.5 percentage points for salmeterol xinafoate and 4 percentage points for placebo. The mean evening PEF-PP followed a similar although less pronounced trend which was significant only during the first 4 weeks of treatment (P = .014). Daytime relief medication and recorded symptoms were reduced significantly in both groups. There was a greater improvement in the number of symptom-free days during the first 4 weeks (P < .01) and the last 4 weeks (P < .05) of treatment for salmeterol xinafoate. The overall incidence and nature of minor adverse events was similar in both groups. CONCLUSIONS This study demonstrates that the addition of salmeterol xinafoate to inhaled corticosteroid therapy in symptomatic asthmatic children significantly improves morning PEF-PP, and reduces their symptoms and use of relief medication.

Relationships between time of day, day of the week, and positive mood: exploring the role of the mood measure

Abstract: This study examined the relationship between time of day, day of the week, and two measures of positive affect (PA). According to previous research and the circumplex model of affect, one scale was designed to assess the activation component of PA, and the other one measured the pleasantness aspect. Subjects rated their mood three times a day for 7 consecutive days. Consistent with our hypotheses, PA-Pleasantness showed a peak on the weekend, whereas PA-Activation remained stable throughout the week. Regarding time of day, maximum PA-Activation was reached in the afternoon. In contrast, the Pleasantness component of PA increased from morning to evening. Implications of these results as well as other findings concerning the differential content of “PA” measures are discussed regarding the fact that a certain scale is most appropriate and maximally valid for representing certain aspects of affective experience.

Circadian rhythm of cortisol confounds cortisol responses to exercise: implications for future research

Abstract: To investigate whether measurements of cortisol responses to exercise are confounded by neglect of the hormone's circadian rhythm, we measured the serum and salivary cortisol responses of eight women to 40 min of 70% maximal oxygen consumption treadmill exercise beginning at 0800 and 2000. Responses were calculated relative to the usually employed preexercise concentrations and also to concentrations at the same times of another day while subjects were at rest. Compared with areas under response curves (AUCs) calculated relative to their circadian baselines, AUCs for serum and salivary cortisol calculated by reference to preexercise concentrations were underestimated (serum, P < 0.001; salivary, P < 0.01) by 93 and 84% in the morning and by 37 and 35% in the evening, respectively. Calculated by the usual preexercise baseline method, rises in serum and salivary cortisol were similarly underestimated. More accurately calculated relative to their circadian baselines, serum and salivary cortisol AUCs were similar (P = 0.63 and P = 0.37, respectively) in the morning and evening, as were their rises (P = 0.23 and P = 0.70, respectively). In future investigations of the existence and magnitude of cortisol responses, those responses must be calculated relative to the hormone's circadian baseline.

Comparative effect of night and daytime sleep on the 24-hour cortisol secretory profile.

Abstract: To determine whether cortisol secretion interacts with daytime sleep in a similar manner to that reported for night sleep, 14 healthy young men were studied during two 24-hour cycles. During one cycle they slept during the night, during the other the sleep period was delayed by 8 hours. Secretory rates were calculated by a deconvolution procedure from plasma cortisol, measured at 10-minute intervals. The amount of cortisol secreted during night sleep was lower than during the corresponding period of sleep deprivation (12.7 +/- 1.1 vs. 16.3 +/- 1.6 mg; p < 0.05), but daytime sleep beginning at the habitual time of morning awakening failed to inhibit cortisol secretion significantly. There was no difference between the amount of cortisol secreted from 0700 to 1500 hours in sleeping subjects and in subjects who were awake during the same period of time (24.2 +/- 1.5 vs. 22.5 +/- 1.4 mg). Even if the comparison between sleeping and waking subjects was restricted to the period 0700-1100 hours or 0700-0900 hours, no significant difference was found. Neither secretory pulse amplitude nor frequency differed significantly in either period. However, detailed analysis of the secretory rates in day sleepers demonstrated a transient decrease in cortisol secretion at about the time of sleep onset, which began 10 minutes before and lasted 20 minutes after falling asleep. Spontaneous or provoked awakenings had a determining influence on the secretory profiles. Ten to 20 minutes after awakening from either night or day sleep cortisol secretion increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of timing of shifts on sleepiness and sleep duration.

Abstract: SUMMARY This review summarizes the effects on sleep duration and sleepiness of (1) the timing of shifts (start and finishing times) and (2) the scheduling of free time between shifts. The results from the few studies available show that sleep duration is clearly determined by the change over time between the night and the morning shift—no more than 5 or 6 hours of sleep is obtained before the morning shift if the shift starts at 06.00 hours or earlier. Therefore, it is suggested that the morning shift should not start before 07.00 hours. A late start of the morning shift will however, increase the sleepiness at the end of the night shift, as well as decrease the duration of the daysleep after the night shift. On the other hand, one may argue that the short daysleep after a night shift may be compensated for by an evening nap, whereas a short night sleep before a morning shift cannot (no time for nap). The review of studies concerning free time between shifts suggests that at least 16 hours is needed and that quick change-overs should be avoided. The free time after a spell of night shifts should be at least 48 hours since the shiftworker needs two main sleep episodes to recover from night work.

Light treatment in seasonal and nonseasonal depression

Abstract: Ninety patients with major depressive disorder were classified according to seasonal (n = 68, 50 women) or nonseasonal (n = 22, 17 women) pattern according to DSM-III-R. They were also clinically evaluated and rated before and after morning (0600-0800) or evening (1800-2000) light treatment for 10 days in a room with a luminance of 350 cd/m2 (approximately 1500 lx) at eye level. Mood ratings were performed using both the Comprehensive Psychopathological Rating Scale and the Hamilton Depression Rating Scale. Depressed patients with seasonal pattern improved significantly more than those with a nonseasonal pattern suggesting a specific nonplacebo effect of light treatment in depressed patients with seasonal pattern. There were no significant differences in outcome when light treatment was given in the morning or in the evening, and not between patients with and without atypical symptoms such as carbohydrate craving or increased appetite.

Diurnal Cycle of Oceanic Precipitation from SSM/I Data

Abstract: Four and a half years of the global monthly oceanic rain rates derived from the DMSP (Defense Meteorological Satellite Program) F-8 SSM/I (Special Sensor Microwave/Imager) data are used to study the diurnal cycles. Annual mean rainfall maps based on the SSM/I morning and evening observations are presented, and their differences are examined using a paired t test. The morning estimates are larger than the afternoon estimates by about 20% over the oceanic region between 50°S and 50°N, with significant differences located mainly along the intertropical convergence zone region. Using the measurements from two satellites, either DMSP F-8 and F-10 or DMSP F-10 and F-11, amplitudes and phases of the 24-h harmonic are estimated. The diurnal cycle shows a nocturnal or early morning maximum in 35%–40% of the oceanic regions. Monte Carlo simulations show that the rms errors associated with the estimated amplitude and phase are about 100% and 2 h, respectively, mainly due to the large random errors (50%) ass...

Feasibility Study of N-of-1 Trials With Blood Pressure Self-Monitoring in Hypertension

Abstract: The objective of this study was to assess individual responses to antihypertensive treatment by N-of-1 trials using blood pressure self-monitoring in 79 patients of both sexes referred to a hypertension clinic. Thirty-five patients who remained untreated (study 1) and 44 N-of-1 trial participants (study 2) were consecutively selected if their clinic blood pressure was between 160/95 and 220/115 mm Hg and there were no hypertensive complications. Blood pressure was measured daily at home for 21 days (three consecutive measures, morning and evening). Each N-of-1 trial was a single-blind treatment consisting of two successive 10-day treatment pairs, each pair comprising 5 days of placebo followed by 5 days of 20 mg enalapril once daily in the morning. Study 1 showed no significant blood pressure regression toward the mean over 20 days and justified the choice of 5-day treatment periods in study 2. In study 2, blood pressure fell significantly 12 hours after the first administration of enalapril and rose within 24 hours of the end of the 5-day active treatment period. Using evening blood pressure values (12 hours after enalapril intake) from the first treatment pair, 33 patients were classified as responders (diastolic blood pressure fall > or = mm Hg). In 16 of these 33 patients, the fall in blood pressure above 6 mm Hg was not maintained in the morning, 24 hours after drug intake. Response reproducibility was tested by comparison with the second treatment pair: the observed agreement was only 0.71 (chance-corrected agreement: 0.34) when defined according to both evening and morning values.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin Marks Circadian Phase Position and Resets the Endogenous Circadian Pacemaker in Humans

Abstract: Measuring the dim light melatonin onset (DLMO) is a useful and practical way to assess circadian phase position in humans. As a marker for the phase and period of the endogenous circadian pacemaker, the DLMO has been shown to advance with exposure to bright light in the morning and to delay with exposure to bright light in the evening. This 'phase response curve' (PRC) to light has been applied in the treatment of winter depression, jet lag and shift work, as well as circadian phase sleep disorders. Exogenous melatonin has phase-shifting effects described by a PRC that is about 12 h out of phase with the PRC to light. That is, melatonin administration in the morning causes phase delays and in the afternoon causes phase advances. All of the circadian phase disorders that have been successfully treated with appropriately timed exposure to bright light can be treated with appropriately scheduled melatonin administration. Melatonin administration is more convenient and therefore may be the preferred treatment.

Seasonal differences in diurnal blood pressure of hypertensive patients living in a stable environmental temperature.

Abstract: Objective : To determine whether there is a seasonal variation in blood pressure in hypertensive patients whose daily lifestyle is similar in summer and in winter, and who live almost entirely indoors in a stable environmental temperature. Subjects and methods : During summer and winter, blood pressure was measured by ambulatory blood pressure monitoring in outpatients with essential hypertension, and environmental temperature was measured by electrothermometer while the patients were awake. The 24-h blood pressure data were analysed after being divided into four groups : morning, afternoon, night-time and sleeping periods. Results : We studied 25 outpatients (mean ± SD age 57 ± 12 years) who spend virtually the entire day indoors in both summer and winter. Measurements of systolic and diastolic blood pressure in the morning and night-time periods were significantly higher in winter than in summer (differences of 7.5 ± 14.7 and 4.1 ± 8.8 mmHg and 8.2 ± 14.8 and 4.5 ± 18.1 mmHg, respectively). Blood pressure measured in the afternoon and during sleeping periods did not differ significantly. No correlation was observed between the seasonal change in blood pressure in the morning and that at night. Environmental temperatures were significantly higher in the morning, afternoon and night-time periods during summer than those during winter. The differences among these periods were not statistically significant. Conclusions : There is a seasonal variation in blood pressure in the morning and night-time periods during winter in hypertensive patients who live essentially indoors in a relatively stable environmental temperature. Pressor factor(s) may differ between morning and night-time periods during winter.

Morning Sympathetic Nerve Activity Is Not Increased in Humans Implications for Mechanisms Underlying the Circadian Pattern of Cardiac Risk

Abstract: Background The sympathetic nervous system has been implicated in the circadian pattern of myocardial infarction and sudden death. It has been postulated that sympathetic nerve activity is higher in the morning than at other times of the day and that this increase reflects an endogenous circadian pattern or is triggered by changes in posture and the onset of morning activities. Methods and Results To test these two concepts, we made microneurographic recordings of muscle sympathetic nerve activity in the morning (6:30 to 8:30 am) and afternoon (2:00 to 4:00 pm) in eight healthy subjects (mean age, 42±4 years), and intraindividual comparisons (paired t tests) were made during (1) supine rest, (2) postural changes simulated by lower body negative pressure (LBNP), and (3) activity produced by sustained handgrip. Plasma cortisol, known to follow a circadian pattern, was measured to assess whether normal circadian patterns were present under experimental conditions. Plasma cortisol exhibited a robust circadian variability (plasma cortisol [mean±SEM], am versus pm: 17±1 versus 9±1 μg/dL, P =.008). In contrast, basal muscle sympathetic nerve activity was not higher in the morning compared with the afternoon (group mean sympathetic nerve activity, am versus pm: 38±6 versus 38±6 bursts per minute, P =NS). Similarly, plasma norepinephrine levels were not higher in the morning compared with the afternoon (plasma norepinephrine, am versus pm: 157±17 versus 173±14 pg/mL, P =NS). During postural stress simulated by LBNP, the magnitude of change in sympathetic nerve activity was not higher in the morning compared with the afternoon (LBNP −20 mm Hg, am versus pm: 103±34% versus 157±31%, P =NS). Finally, the magnitude of change in muscle sympathetic nerve activity during the first minute of handgrip exercise (am versus pm: 11±17% versus 8±11%, P =NS) or the second minute of handgrip exercise (am versus pm: 59±34% versus 60±15%, P =NS) was not higher in the morning compared with the afternoon. Conclusions These findings challenge the concept that sympathetic nerve activity is higher in the morning either during supine rest or during postural changes and activity. We speculate that if the sympathetic nervous system is involved in the circadian pattern of sudden death, this involvement must reflect exaggerated morning end-organ responsiveness to norepinephrine, not enhanced morning sympathetic outflow.

Chronobiology and chronotherapy in medicine

Abstract: There is a fascinating and exceedingly important area of medicine that most of us have not been exposed to at any level of our medical training. This relatively new area is termed chronobiology; that is, how time-related events shape our daily biologic responses and apply to any aspect of medicine with regard to altering pathophysiology and treatment response. For example, normally occurring circadian (daily cycles, approximately 24 hours) events, such as nadirs in epinephrine and cortisol levels that occur in the body around 10 PM to 4 AM and elevated histamine and other mediator levels that occur between midnight and 4 AM, play a major role in the worsening of asthma during the night. In fact, this nocturnal exacerbation occurs in the majority of asthmatic patients. Because all biologic functions, including those of cells, organs, and the entire body, have circadian, ultradian (less than 22 hours), or infradian (greater than 26 hours) rhythms, understanding the pathophysiology and treatment of disease needs to be viewed with these changes in mind. Biologic rhythms are ingrained, and although they can be changed over time by changing the wake-sleep cycle, these alterations occur over days. However, sleep itself can adversely affect the pathophysiology of disease. The non-light/dark influence of biologic rhythms was first described in 1729 by the French astronomer Jean-Jacques de Mairan. Previously, it was presumed that the small red flowers of the plant Kalanchoe bloss feldiuna opened in the day because of the sunlight and closed at night because of the darkness. When de Mairan placed the plant in total darkness, the opening and closing of the flowers still occurred on its intrinsic circadian basis. It is intriguing to think about how the time of day governs the pathophysiology of disease. On awakening in the morning, heart rate and blood pressure briskly increase, as do platelet aggregability and other clotting factors. This can be linked to the acrophase (peak event) of heart attacks. During the afternoon we hit our best mental and physical performance, which explains why most of us state that "I am not a morning person." Even the tolerance for alcohol varies over the 24-hour cycle, with best tolerance around 5 pm (i.e. "Doctor, I only have a couple of highballs before dinner"). Thus, all biologic functions, from those of the cell, the tissue, the organs, and the entire body, run on a cycle of altering activity and function.(ABSTRACT TRUNCATED AT 400 WORDS)

Light therapy for seasonal affective disorder. The effects of timing.

Abstract: BACKGROUND Sixty-eight patients with seasonal affective disorder participated in a 10,000-lux light treatment study in which two questions were addressed: do response rates differ when the light is applied at different times of the day and does short-term rank ordering of morning and evening light influence response rates? METHOD Three groups of patients received a 4-day light treatment: (I) in the morning (8.00-8.30 a.m., n = 14), (II) in the afternoon (1.00-1.30 p.m., n = 15) or (III) in the evening (8.00-8.30 p.m., n = 12). Two additional groups of patients received two days of morning light treatment followed by two days of evening light (IV, n = 13) or vice versa (V, n = 14). RESULTS Response rates for groups I, II and III were 69, 57 and 80% respectively, with no significant differences between them. Response rates for groups IV and V were 67 and 50% respectively; this difference was not significant and these percentages did not differ significantly from those of groups I and III. CONCLUSIONS The results indicate that the timing of light treatment is not critical and that short-term rank ordering of morning and evening light does not influence therapeutic outcome.

Sympathetic Activity as the Cause of the Morning Increase in Cardiac Events: A Likely Culprit, but the Evidence Remains Circumstantial

Abstract: The well-documented morning increase in myocardial infarction, sudden cardiac death, and other cardiovascular disorders provides a new opportunity to identify the causes of disease onset. In this issue of Circulation , Middlekauff and Sontz1 report on efforts to determine whether the sympathetic nervous system is responsible for the increase in disease onset in the morning. They have picked a prime candidate for a causal role, because (1) events associated with increased sympathetic discharge, such as heavy exertion, have been shown to trigger infarction onset2 ; (2) morning is a time associated with a transition from low to high sympathetic activity3 ; and (3) both observational and randomized studies have demonstrated elimination of the morning peak of disease onset in individuals receiving β-adrenergic blocking agents.4 5 Middlekauff and Sontz directly measured firing rates of sympathetic nerves to skeletal muscle at rest and during stress in the morning and afternoon. The study was conducted in eight healthy subjects who had spent the previous night in the Clinical Research Center. The morning measurements (obtained between 6:30 and 8:30 am) were compared with afternoon measurements (obtained between 2 and 4 pm). After basal levels were recorded, lower-body negative pressure was applied (to simulate the stress of assuming the upright …

The Hypothalamic-Pituitary-Adrenal Axis in Obesity

Abstract: The hypothalamic-pituitary-adrenal (HPA) axis normally maintains the concentration of Cortisol within a narrow range with a diurnal variation characterized by higher Cortisol concentrations in the morning and reduced levels in the evening. Excessive or deficient secretion of Cortisol is associated with pathologic changes. Obesity has been linked with age, sex and racial alterations in the functioning of the HP A axis which are reviewed. The possible relationship of altered HPA axis activity with the long-term complications of obesity are considered.

Reconstructions of populations of luteinizing hormone releasing hormone neurons in young and middle-aged rats reveal progressive increases in subgroups expressing Fos protein on proestrus and age-related deficits.

Abstract: Fos expression has been used as a marker of activation of neuroendocrine cells including LHRH neurons. In this study, Fos protein was localized within LHRH neurons in young and middle-aged rats to trace the temporal and spatial pattern of LHRH neuronal activation associated with the preovulatory LH surge. Animals were killed during the late morning, afternoon, and evening of proestrus. Dual immunocytochemical protocols localized LHRH and LHRH/Fos neurons, and computer-assisted methods were used to reconstruct forebrain populations of single- and double-labeled LHRH neurons. Although a significant increase in the number of LHRH/Fos neurons was noted by evening in both age groups, a greater increase was observed in young (12% in morning, 28% in afternoon, and 62% by evening) compared with aging females (5% in morning, 10% in afternoon, and 40% by evening). Reconstructions of LHRH and LHRH/Fos neurons revealed time- and age-dependent differences in Fos expression within LHRH neurons. In young females, LHRH/F...

Sleep propensity and sleep architecture after bright light exposure at three different times of day

Abstract: SUMMARY The aim of this work was to study the effects of bright light-induced circadian phase shifts on sleep propensity and sleep architecture while the timing of the sleep/wake cycle is kept constant. Twenty-three normal subjects underwent an 11-day study including: (i) baseline sleep and vigilance evaluation; (ii) baseline evaluation of the circadian temperature rhythm with a 40-h constant routine; (iii) five hours of bright light exposure on each of three days; (iv) post-treatment sleep and vigilance evaluation; (v) post-treatment circadian rhythm evaluation with a second 40-h constant routine. Subjects were divided into three groups: eight subjects were exposed to bright light in the morning (‘Morning group’), eight subjects were exposed in the evening (‘Evening group’), and seven subjects were exposed in the afternoon (‘Afternoon group’). After light exposure, the Morning group showed an advance of 1.23 h in the phase of the temperature rhythm, the Evening group showed a delay of 1.62 h, and the Afternoon group showed a non-significant advance of 0.5 h. In support of expectations, early-night sleep propensity was decreased by evening bright light, was increased in almost all subjects exposed to morning bright light, and was not changed by afternoon bright light exposure. The phase shift created by bright light exposure did not seem to be large enough to have a systematic effect on sleep consolidation or on REM sleep parameters in any of the three groups, suggesting that these variables are less sensitive to alterations in phase of the circadian oscillator than early-night sleep propensity.