Reduced melatonin synthesis in pregnant night workers: Metabolic implications for offspring.

Several novel animal studies have shown that intrauterine metabolic programming can be modified in the event of reduced melatonin synthesis during pregnancy, leading to glucose intolerance and insulin resistance in the offspring. It is therefore postulated that female night workers when pregnant may expose the offspring to unwanted health threats. This may be explained by the fact that melatonin is essential for regulating energy metabolism and can influence reproductive activity. Moreover, the circadian misalignment caused by shift work affects fertility and the fetus, increasing the risk of miscarriage, premature birth and low birth weight, phenomena observed in night workers. Thus, we hypothesize that light-induced melatonin suppression as a result of night work may alter intrauterine metabolic programming in pregnant women, potentially leading to metabolic disorders in their offspring.

Melatonin profiles during the third trimester of pregnancy and health status in the offspring among day and night workers: A case series.

Successful pregnancy requires adaptation in maternal physiology. During intrauterine life the mother's circadian timing system supports successful birth and postnatal development. Maternal melatonin is important to transmit circadian timing and day length to the fetus. This study aims to describe the third trimester of pregnancy among day (n = 5) and night (n = 3) workers by assessing their melatonin levels in a natural environment. Additionally, we describe the worker's metabolic profiles and compare the health status of the newborns between groups of day and night working mothers. Our results indicate an occurrence of assisted delivery (cesarean and forceps) among night workers. Moreover, the newborns of night workers showed lower Apgar index and breastfeeding difficulty indicating a worse condition to deal with the immediate outside the womb environment. Additionally, there was lower night-time melatonin production among pregnant night workers compared to day workers. These findings may be related to light-induced suppression of melatonin that occurs during night work. We conclude that night work and consequent exposure to light at unconventional times might compromise the success of pregnancy and the health of the newborn. Further studies need to be carried out to monitor pregnancy and newborn health in pregnant night workers.

Sleep patterns in Amazon rubber tappers with and without electric light at home.

Today's modern society is exposed to artificial electric lighting in addition to the natural light-dark cycle. Studies assessing the impact of electric light exposure on sleep and its relation to work hours are rare due to the ubiquitous presence of electricity. Here we report a unique study conducted in two phases in a homogenous group of rubber tappers living and working in a remote area of the Amazon forest, comparing those living without electric light (n = 243 in first phase; n = 25 in second phase) to those with electric light at home (n = 97 in first phase; n = 17 in second phase). Questionnaire data (Phase 1) revealed that rubber tappers with availability of electric light had significantly shorter sleep on work days (30 min/day less) than those without electric light. Analysis of the data from the Phase 2 sample showed a significant delay in the timing of melatonin onset in workers with electric light compared to those without electric light (p < 0.01). Electric lighting delayed sleep onset and reduced sleep duration during the work week and appears to interfere with alignment of the circadian timing system to the natural light/dark cycle.

Time of day type of food--relation to mood and hunger during 24 hours of constant conditions.

A six-day high-carbohydrate meal (HC; 65 E% (energy percent) carbohydrates, 20 E% fat and 15 E% protein) and a six-day high-fat meal (HF; 40 E% carbohydrates, 45 E% fat and 15 E% protein) were given to seven healthy subjects in a crossover design. On the last day subjects were kept awake for 24 hours in a metabolic laboratory while substrate utilisation and energy expenditure were measured by indirect calorimetry. The subjects were given isocaloric meals every four hours. Results showed that hunger decreased at night (F = 4.2, p < 0.05) and linearly increased after meal intake. Macronutrient composition (fat/carbohydrates) seemed to be of less importance for hunger. Hunger and thirst were found to be strongly associated with gastrointestinal substances, for hunger the strongest being a negative correlation with triacylglycerol (partial correlation = -0.39). It is suggested that it might not be necessary for shift workers to eat full portions at night but that satiation will occur with less food. Possibly lack of adjustment of nocturnal food intake might be one reason why overweight is common in shift work populations.

Eastward long distance flights, sleep and wake patterns in air crews in connection with a two-day layover.

The present study describes the spontaneous sleep/wake pattern in connection with an eastward (Stockholm to Tokyo, +8 h) transmeridian flight and short (51 h) layovers. To describe all sleep episodes and the recovery process across 4 days, and to relate adjustment to individual differences, 49 Scandinavian Airlines System (SAS) air crew were monitored for 9 days with activity monitors and sleep/wake diary before-during-after flight. The outbound flight involved a period of wakefulness extended to 21 h, frequently (87% of air crew) terminated by a long nap in Tokyo which was calm but difficult to wake up from. Then followed two night oriented sleep periods of normal length but of reduced efficiency, containing many and long awakenings. Napping was common during the extended periods of wakefulness, particularly during flights. During the recovery days, ease of rising from sleep in the mornings was difficult throughout, and feelings of not being refreshed returned to baseline levels on the third recovery sleep. Elevated daytime sleepiness (24% of the day) was observed on the first recovery day. No individual differences related to gender, age or position (cabin/pilot) was found in sleep strategy. Poor adjusters, subjects with a perceived lowered capacity on recovery days, showed more premature awakenings abroad and less refreshing sleep during the last 12 months, suggesting a decreased ability to cope with air crew scheduling. Comparisons with a westbound flight showed the eastbound flight layover sleep to be more problematic and containing more napping.

Retaining home-base sleep hours to prevent jet lag in connection with a westward flight across nine time zones.

The aim of this study was to test a possible countermeasure to jet lag: letting air crew retain their home-base sleep/wake pattern during layover. Instead of their usual adoption of local sleep hours, 19 flight attendants were scheduled to a westward layover (50 h) flight (Copenhagen-Los Angeles, -9 h) on two occasions. On one trip, crews adopted the local sleep pattern, and on the other trip, the crew retained home-base sleep hours. Subjects were monitored for 10 days before, during, and after the flight; they wore activity loggers and gave ratings through sleep/wake diaries and a questionnaire. Ratings of jet lag symptoms and sleepiness were greatly reduced during layover, but not at home, for the home-base condition. It was also found that jet lag feelings seemed to be related mainly to mean sleepiness ratings (multiple regression; 16%, beta = 0.46) and to the number of awakenings (6%, beta = 0.29) during sleep. It is concluded that retaining the home-base sleep pattern may reduce jet lag during layover.

Sleep and wake patterns in aircrew on a 2-day layover on westward long distance flights.

BACKGROUND: As part of a research program of sleep/wake disturbances in connection with irregular work hours and time zone transitions, the study aimed to describe the spontaneous sleep/wake pattern in connection with a westward (Stockholm to Los Angeles) transmeridian flight (-9 h) and short layover (50 h). HYPOTHESIS: To describe all sleep episodes and the recovery process across 4 d, and to relate adjustment to individual differences. METHODS: We monitored 42 SAS aircrew for 9 d with activity monitors and diary before, during, and after flight. RESULTS: During the outbound day the wake span was 21.7 h and 90% of the aircrew adopted local bed times on layover. The readaptation to normal sleep/wake patterns were rapid on the return. Napping was common (93%), especially on-board and before the return. Sleep efficiency dropped below 90% during layover, being felt to be too short and disturbed by awakenings, and gradually returned to normal across four recovery days. Recovery sleep was characterized by difficulties waking up and feelings of not being refreshed from sleep. Sleepiness symptoms increased during layover and gradually decreased across recovery days, still being elevated on day 4. CONCLUSIONS: In the present study we found that westward flights are associated with extended wake spans during layover, increased sleepiness, and slow recovery on return home. Strategic sleeping may counteract the effect somewhat, but individual differences are few.

Effects of alternating 8- and 12-hour shifts on sleep, sleepiness, physical effort and performance.

OBJECTIVES: The aim of the present study was to compare 12-hour shifts during weekends with 8-hour shifts during weekdays with respect to sleep, sleepiness, physical effort, and performance. METHODS: Thirty-one subjects at a power plant participated. Sleep, sleepiness, and physical effort were measured with a diary. About half of the subjects carried out a reaction-time test during both 8- and 12-hour morning and night shifts. The remaining subjects carried out a vigilance task. RESULTS: Sleepiness was higher and physical effort lower on the 12-hour night shift than on the 8-hour night shift. However, the subjects who had the same level of physical effort on 8- and 12-hour night shifts did not differ with respect to sleepiness. During the 12-hour morning shift, sleepiness was lower and the sleep length was longer than on the 8-h morning shift. The subjects who had the same amount of sleep for 8- and 12-hour morning shifts showed no difference in sleepiness. Sleep did not differ between 8- and 12-hour night shifts. There was no difference between 8- and 12-hour shifts with respect to performance. CONCLUSIONS: It was suggested that the difference in sleepiness between 8- and 12-hour shifts is related to differences in sleep length for the morning shift, and to differences in physical effort for the night shift, rather than to shift duration. Thus the most likely conclusion is that 12-hour shifts do not cause increased sleepiness or impaired performance or disturbed sleep.

Change from an 8-hour shift to a 12-hour shift, attitudes, sleep, sleepiness and performance.

OBJECTIVES: The present study sought to evaluate the effect of a change from a rotating 3-shift (8-hour) to a 2-shift shift (12 hour) schedule on sleep, sleepiness, performance, perceived health, and well-being. METHODS: Thirty-two shift workers at a chemical plant (control room operators) responded to a questionnaire a few months before a change was made in their shift schedule and 10 months after the change. Fourteen workers also filled out a diary, carried activity loggers, and carried out reaction-time tests (beginning and end of shift). Fourteen day workers served as a reference group for the questionnaires and 9 were intensively studied during a week with workdays and a free weekend. RESULTS: The questionnaire data showed that the shift change increased satisfaction with workhours, sleep, and time for social activities. Health, perceived accident risk, and reaction-time performance were not negatively affected. Alertness improved and subjective recovery time after night work decreased. The quick changes in the 8-hour schedule greatly increased sleep problems and fatigue. Sleepiness integrated across the entire shift cycle showed that the shift workers were less alert than the day workers, across workdays and days off (although alertness increased with the 12-hour shift). CONCLUSIONS: The change from 8-hour to 12-hour shifts was positive in most respects, possibly due to the shorter sequences of the workdays, the longer sequences of consecutive days off, the fewer types of shifts (easier planning), and the elimination of quick changes. The results may differ in groups with a higher work load.

Morning work: effects of early rising on sleep and alertness.

The aim of the present study is to investigate how early morning work affects sleep and alertness. Twenty-two females, employed as airline cabin crew members, participated in the study. The design included two sleep conditions (work day and free day) for an early group and for a control group. The results show that early morning work reduced sleep to 5 hours and 12 minutes and that the reduction of sleep consisted of less stage 2 and rapid eye movement (REM) sleep. However, when the analysis was restricted to the first 5 hours, no differences in sleep stages, arousals, or sleep continuity were obtained between groups or conditions. Analysis of electroencephalogram (EEG) power density for the 0.5-16.5 Hz bands across nonREM periods showed no differences. With respect to the subjective ratings, early morning work was associated with more apprehension of difficulties in awakening and insufficient sleep. Daytime alertness and ease of awakening did not differ between groups, but the early group had significantly more sleepiness and complained more of unrefreshing sleep in connection with the work day compared to the free day. Ratings of insufficient sleep and high daytime sleepiness were mainly predicted (multiple regression analyses) by short total sleep time (TST), whereas apprehension of an unpleasant awakening was predicted by an early wake-up time. It was concluded that early morning work causes a reduction of sleep time and an increase in apprehension stress.