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Background: Older men often experience nocturnal urination difficulties, reflected by diurnal differences in maximum urine flow (Qmax). Since lower urinary tract symptoms and pathological comorbidities are frequent in older men, it remains unclear whether this diurnal variation is a physiological or pathological phenomenon. Our aim was to quantify the diurnal variability of Qmax in healthy young participants under varying daylight conditions in a stable environment to discern potential underlying causes of nocturnal urination difficulties., Methods: Twenty-one healthy young men were recruited in a 4-day study utilizing daytime (08:00-18:00) exposure with two light conditions in randomized order: dim (< 50 lx) or bright (~2500 lx). Day 1 was for acclimation, and urine flow was assessed from day 2. The participants urinated ad libitum during day 2 and then at fixed 3-4-h intervals thereafter (days 3-4). Regular urination Qmax at late night (04:00) on day 4 was compared with the nearest voided volume during daytime of day 3 (mDay)., Results: Morning Qmax scores (after bed-11:00) on day 2 were significantly lower than evening (17:00-before pre-sleep) in bright conditions and those of daytime (11:00-17:00), evening (17:00-before pre-sleep), and pre-sleep in dim conditions. Pre-sleep Qmax during the ad libitum period was significantly higher in dim than bright conditions. Late-night Qmax values (04:00) on day 4 were significantly lower than Qmax scores of mDay on day 3 in both light conditions., Conclusions: Healthy young men had a clear diurnal Qmax difference that decreased during late night and morning. In addition, the pre-sleep Qmax values in dim daylight were significantly higher than in bright daylight. Taken together, we conclude that late-night and morning decreases in Qmax are an instinctive physiological phenomenon in humans, and the diurnal difference of Qmax can be influenced by daylight conditions., (© 2023. The Author(s).)

In humans, most renal functions, including urine volume and electrolyte excretions, have a circadian rhythm. Light is a strong circadian entrainment factor and daytime-light exposure is known to affect the circadian rhythm of rectal temperature (RT). The effects of daytime-light exposure on the diurnal rhythm of urinary excretion have yet to be clarified. The aim of this study was to clarify whether and how daytime exposure to bright-light affects urinary excretions. Twenty-one healthy men (21-27 years old) participated in a 4-day study involving daytime (08:00-18:00 h) exposure to two light conditions, Dim (< 50 lx) and Bright (~ 2500 lx), in a random order. During the experiment, RT was measured continuously. Urine samples were collected every 3 ~ 4 h. Compared to the Dim condition, under the Bright condition, the RT nadir time was 45 min earlier (p = 0.017) and sodium (Na), chloride (Cl), and uric acid (UA) excretion and urine volumes were greater (all p < 0.001), from 11:00 h to 13:00 h without a difference in total daily urine volume. The present results suggest that daytime bright light exposure can induce a phase shift advance in urine volume and urinary Na, Cl, and UA excretion rhythms.

Background: The aim of this study is to clarify associations between orthostatic blood pressure (BP) change, as well as possible physiological factors, and day-to-day home BP variability, a promising risk factor for cardiovascular outcomes., Methods: Study participants were 6,465 community residents (age 58.3 years). Home BP was measured every morning and evening for 7 days. Orthostatic BP was calculated as the maximum difference between BP measured while sitting and remeasured after 1 and 3 minutes standing., Results: Frequency of individuals who showed orthostatic BP decline was as follows: systolic BP (SBP) change ≥-20 mm Hg: 2.6%, ≥-10 mm Hg: 14.1%. These subgroups showed larger home SBP variability (average real variability: 11.3 ± 5.3, 8.7 ± 3.9 mm Hg) when compared with orthostatic normotensives (7.6 ± 3.7 mm Hg) (all P < 0.001). Multiple linear regression analysis adjusted for major covariates, including seated BP, identified orthostatic BP drop as an independent determinant for morning BP variability (≥-20 mm Hg: β = 0.037, P = 0.003; ≥-10 mm Hg: β = 0.026, P = 0.036) but not for evening BP variability. Carotid hypertrophy was significantly associated with home BP variability (morning: β = 0.052, P = 0.001; evening: β = 0.065, P < 0.001) and showed a U-shaped association with orthostatic BP change. Plasma B-type natriuretic peptide level, a previously suggested factor for BP variability, did not show significant association with morning and evening BP variability., Conclusion: Orthostatic BP decline was significantly associated with morning BP variability. Large artery atherosclerosis was a common risk factor.

Objective: Abnormalities in circadian blood pressure (BP) variation, particularly increase in nocturnal BP, have been reported to be risk factors for cardiovascular disease, although the factors associated with BP abnormalities are not fully understood. This study aimed to clarify possible associations of sleep characteristics, including sleep fragmentation, sleep disordered breathing, and nocturia, with sleep BP by simultaneous multiday measurements., Methods: A cross-sectional study evaluated 5959 community participants having home-measured data on nocturnal BP change (sleep BP - awaking BP), sleep characteristics, and sleep disordered breathing. Sleep characteristics including the fragmentation index were assessed using wrist-wearable actigraphy, whereas sleep disordered breathing was assessed by 3% oxygen desaturation index obtained using a finger-type monitor. The number of nocturnal urinations was recorded in a sleep diary., Results: Mean nocturnal SBP change was -8.5 ± 7.9%. A 3% oxygen desaturation index was associated with the BP change independently of the basic covariates (β = 0.051, P = 0.001), although the association became insignificant (P = 0.196) after adjusting the fragmentation index (β = 0.105, P < 0.001). The association of the fragmentation index was also insignificant (P = 0.153) after adjusting measurement season (middle season: β = 0.163, P < 0.001; summer season: β = 0.249, P < 0.001). In contrast, the frequency of urination showed strong and independent association (β = 0.140, P < 0.001), with smaller nocturnal BP drop in participants with frequent urination., Conclusion: Subjective sleep estimates and frequent nocturnal urination may represent a potential risk for circadian BP abnormalities.

The guidelines for night and shift workers recommend that after night work, they should sleep in a dark environment during the daytime. However, staying in a dark environment during the daytime reduces nocturnal melatonin secretion and delays its onset. Daytime bright-light exposure after night work is important for melatonin synthesis the subsequent night and for maintaining the circadian rhythms. However, it is not clear whether daytime sleeping after night work should be in a dim- or a bright-light environment for maintaining melatonin secretion. The aim of this study, therefore, was to evaluate the effect of bright-light exposure during daytime sleeping on nocturnal melatonin secretion after simulated night work. Twelve healthy male subjects, aged 24.8 ± 4.6 (mean ± SD), participated in 3-day sessions under two experimental conditions, bright light or dim light, in a random order. On the first day, the subjects entered the experimental room at 16:00 and saliva samples were collected every hour between 18:00 and 00:00 under dim-light conditions. Between 00:00 and 08:00, they participated in tasks that simulated night work. At 10:00 the next morning, they slept for 6 hours under either a bright-light condition (>3000 lx) or a dim-light condition (<50 lx). In the evening, saliva samples were collected as on the first day. The saliva samples were analyzed for melatonin concentration. Activity and sleep times were recorded by a wrist device worn throughout the experiment. In the statistical analysis, the time courses of melatonin concentration were compared between the two conditions by three-way repeated measurements ANOVA (light condition, day and time of day). The change in dim light melatonin onset (ΔDLMO) between the first and second days, and daytime and nocturnal sleep parameters after the simulated night work were compared between the light conditions using paired t-tests. The ANOVA results indicated a significant interaction (light condition and3 day) (p = .006). Post hoc tests indicated that in the dim-light condition, the melatonin concentration was significantly lower on the second day than on the first day (p = .046); however, in the bright-light condition, there was no significant difference in the melatonin concentration between the days (p = .560). There was a significant difference in ΔDLMO between the conditions (p = .015): DLMO after sleeping was advanced by 11.1 ± 17.4 min under bright-light conditions but delayed for 7.2 ± 13.6 min after sleeping under dim-light conditions. No significant differences were found in any sleep parameter. Our study demonstrated that daytime sleeping under bright-light conditions after night work could not reduce late evening melatonin secretion until midnight or delay the phase of melatonin secretion without decreasing the quality of the daytime sleeping. Thus, these results suggested that, to enhance melatonin secretion and to maintain their conventional sleep-wake cycle, after night work, shift workers should sleep during the daytime under bright-light conditions rather than dim-light conditions.

Background: The purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality (by using actigraphy and the OSA sleep inventory) and melatonin secretion at night., Methods: Thirty three male University students (mean ± SD age: 22 ± 3.1 years) completed the experiments lasting 5 days and 4 nights. The subjects were randomly divided into four groups: Poor*Dim (n = 10), meaning a tryptophan-poor breakfast (55 mg/meal) in the morning and dim light environment (<50 lx) during the daytime; Rich*Dim (n = 7), tryptophan-rich breakfast (476 mg/meal) and dim light environment; Poor*Bright (n = 9), tryptophan-poor breakfast and bright light environment (>5,000 lx); and Rich*Bright (n = 7), tryptophan-rich breakfast and bright light., Results: Saliva melatonin concentrations on the fourth day were significantly lower than on the first day in the Poor*Dim group, whereas they were higher on the fourth day in the Rich*Bright group. Creatinine-adjusted melatonin in urine showed the same direction as saliva melatonin concentrations. These results indicate that the combination of a tryptophan-rich breakfast and bright light exposure during the daytime could promote melatonin secretion at night; further, the observations that the Rich*Bright group had higher melatonin concentrations than the Rich*Dim group, despite no significant differences being observed between the Poor*Dim and Rich*Dim groups nor the Poor*Bright and Rich*Bright groups, suggest that bright light exposure in the daytime is an important contributor to raised melatonin levels in the evening., Conclusions: This study is the first to report the quantitative effects of changed tryptophan intake at breakfast combined with daytime light exposure on melatonin secretion and sleep quality. Evening saliva melatonin secretion changed significantly and indicated that a tryptophan-rich breakfast and bright light exposure during the daytime promoted melatonin secretion at this time.

This study aimed at elucidating the physiological significance of dusk and dawn in the circadian rhythm of core temperature (T(core)) and urinary 6-hydroxymelatonin sulfate in humans during sleep and the waking sensation just after rising. Seven female and four male students served as participants. Participants retired at 2300 h and rose at 0700 h. They were requested to sit on a chair and spend time as quietly as possible during wakefulness, reading a book or listening to recorded light music. Two lighting conditions were provided for each participant: 1) Light-Dark (LD)-rectangular light change with abrupt decrease from 3,000 lx to 100 lx at 1800 h, abrupt increase from 0 lx to 3,000 lx at 0700 h. 2) LD-twilight light change with gradual decrease from 3,000 lx to 100 lx starting at 1700 h (twilight period about 2 h), with gradual increase from 0 lx to 3,000 lx starting at 0500 h (twilight period about 2 h). The periods of 0 lx at night were from 2300 h to 0700 h on the first day and from 2300 to 0500 h on the second day. Nadir time advanced significantly under the influence of the LD-twilight condition. The amount of 6-hydroxymelatonin sulfate in urine collected at 0200 h was significantly higher under LD-twilight in comparison with LD-rectangular light. Morning drowsiness tended to be lower under LD-twilight. Our results suggest that in architectural design of indoor illumination it is important to provide LD-twilight in the evening and early morning for sleep promotion in healthy normal people and/or light treatment in elderly patients with advanced dementia.

The present experiment aimed at knowing how a gradual changes of room temperature (T(a)) and light in the evening and early morning could influence circadian rhythms of core temperature (T(core)), skin temperatures, urinary 6-hydroxymelatonin sulfate and waking sensation just after rising in humans. Two kinds of room environment were provided for each participant: 1) Constant room temperature (T(a)) of 27 degrees C over the 24 h and LD-rectangular light change with abrupt decreasing from 3,000 lx to 100 lx at 1800, abrupt increasing from 0 lx to 3,000 lx at 0700. 2) Cyclic changes of T(a) and with gradual decrease from 3,000 lx to 100 lx onset at 1700 (twilight period about 2 h), with gradual increasing from 0 lx to 3,000 lx onset at 0500 (about 2 h). Main results are summarized as follows: 1) Circadian rhythms of nadir in the core temperature (T(core)) significantly advanced earlier under the influence of gradual changes of T(a) and light than no gradual changes of T(a) and light. 2) Nocturnal fall of T(core) and morning rise of T(core) were greater and quicker, respectively, under the influence of gradual changes of T(a) and light than no gradual changes of T(a) and light. 3) Urinary 6-hydroxymelatonin sulfate during nocturnal sleep was significantly greater under the influence of gradual changes of T(a) and light. 4) Waking sensation just after rising was significantly better under the influence of gradual changes of T(a) and light. We discussed these findings in terms of circadian and thermoregulatory physiology.

The present study investigated whether room temperature (T(a)) cycles around dusk and dawn could influence the circadian rhythm of rectal temperature (T(core)), urinary 6-hydroxymelatonin sulfate during nocturnal sleep, and subjective assessments of sleep in humans. Six female and two male students served as participants. Two different T(a) conditions, cyclic and constant, were established. Two kinds of room temperature were provided to subjects: cyclic T(a) (gradual decrease from 27 degrees C to 24 degrees C between 1800 and 2200 h and gradual increase from 24 degrees C to 27 degrees C between 0300 and 0700 h) and constant T(a) (27 degrees C over 24 h). At cyclic T(a), the circadian nadir of T(core) rhythm was significantly advanced, while T(core) was significantly lower from 2300 to 0200 h and significantly higher from 0600 to 1000 h. The nocturnal concentration of 6-hydroxymelatonin sulfate in the urine during sleep was significantly higher during cyclic T(a). Waking sensation just after rising was significantly better with cyclic T(a). (Skin temperatures in the extremities-T(a)) were significantly higher with cyclic T(a) especially during the evening and night. Our results suggest that gradual change of room temperature in the evening and early morning is important in terms of sleep promotion and fresh awakening. It seems probable that mankind has been evolved to have deeper sleep under the influence of cyclic T(a) around dusk and dawn.

Following the previous studies on the influence of light with different wavelengths on human biological rhythms during nighttime, present experiments were conducted to investigate the influence of morning light on the behavior of the core temperature and melatonin in humans. The experiments were carried out in four subjects with normal color vision. The subjects were exposed between 4:00 h to 9:00 h to red, green and blue light of 1,000 lux and 2,500 lux, and with an incandescent light of 50 lux as control. The main results were as follows: No differences in the behavior of core temperature and melatonin were found under the influences of red, green and blue light of 1,000 lux and the control light of 50 lux. On the other hand, a tendency to promote the increase of core temperature and the fall of melatonin secretion was found after exposure to green light of 2,500 lux, compared with control and red light. These results indicate that the behavior of core temperature and melatonin differs according to the wavelength of light, and that the phenomenon arises with morning as well as nocturnal irradiation. However, the intensity of light required to bring about the phenomenon seems to be different between morning and evening; an irradiation of 1,000 lux x 5h at night in the previous report, and one of 2,500 lux x 5h in the morning in the present experiments, were found to be necessary for green light to cause the effects.