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The response to a zeitgeber, particularly the light/dark cycle, may vary phenotypically. Phenotypic plasticity can be defined as the ability of one genome to express different phenotypes in response to environmental variation. In this opinion paper, we present some evidence that one of the most prominent effects of the introduction of electric light to the everyday life of humans is a significant increase in phenotypic plasticity and differences in interindividual phases of entrainment. We propose that the healthy limits of phenotypic plasticity have been surpassed in contemporary society.

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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.

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BACKGROUND: Fibromyalgia is characterized by chronic widespread pain and sleep disturbances. Overweight and obesity, which lead to metabolic changes, are additional comorbidities that are rarely explored, although they are highly prevalent in patients with fibromyalgia. METHODS: We compared the plasma levels of leptin and acylated ghrelin in 17 women with fibromyalgia (patients) and 16 healthy women (controls) with similar age, anthropometric measurements and levels of physical activity. We also investigated the relationships between these two neuropeptides and sleep and various pain characteristics in patients with fibromyalgia. Anthropometric measurements were recorded, and physical activity levels were assessed using a questionnaire. Pain intensity was measured using visual analogue scales (weekly general and mean pain scores). Sleep was assessed using an accelerometry technique. RESULTS: Compared to the control group, the patient group had increased leptin levels (patients: 22.4 ± 10.6 vs. controls: 13.3 ± 17.9 ng/mL; p < 0.01) and decreased acylated ghrelin levels (patients: 126.7 ± 47.8 vs. controls: 183.3 ± 102.2 pg/mL; p = 0.048). The leptin level was not significantly correlated with any of the variables. Acylated ghrelin level was inversely correlated with the weekly mean pain score (r = -0.67, p < 0.01) and the weekly general pain score (r = -0.67, p < 0.01). Multiple regression analysis revealed that the variations in acylated ghrelin levels accounted for 35% of the weekly general pain and 29% of the weekly mean pain variability. CONCLUSIONS: These findings indicate that the decreased acylated ghrelin levels in women with fibromyalgia are related to pain intensity.

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Inter-individual differences in the phase of the endogenous circadian rhythms have been established. Individuals with early circadian phase are called morning types; those with late circadian phase are evening types. The Horne and Ostberg Morningness-Eveningness Questionnaire (MEQ) is the most frequently used to assess individual chronotype. The distribution of MEQ scores is likely to be biased by several fact, ors, such as gender, age, genetic background, latitude, and social habits. The objective of the present study was to determine the effect of different social synchronizers on the sleep/wake cycle of persons with different chronotypes. Volunteers were selected from a total of 1232 UFPR undergraduate students who completed the MEQ. Thirty-two subjects completed the study, including 8 morning types, 8 evening types and 16 intermediate types. Sleep schedules were recorded by actigraphy for 1 week on two occasions: during the school term and during vacation. Sleep onset and offset times, sleep duration, and mid-sleep time for each chronotype group were compared by the Mann-Whitney U-test separately for school term and vacation. School term and vacation data were compared by the Wilcoxon matched-pair test. Morning types showed earlier sleep times and longer sleep duration compared with evening types (23:00 +/- 44 and 508.9 +/- 50.27 vs 01:08 +/- 61.95 and 456.44 +/- 59.08, for the weekdays during vacation). During vacation, the subjects showed later sleep times, except for the morning types, who did not exhibit differences for sleep onset times. The results support the idea that social schedules have an impact on the expression of circadian rhythmicity but this impact depends on the individual chronotype.

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Inter-individual differences in the phase of the endogenous circadian rhythms have been established. Individuals with early circadian phase are called morning types; those with late circadian phase are evening types. The Horne and Östberg Morningness-Eveningness Questionnaire (MEQ) is the most frequently used to assess individual chronotype. The distribution of MEQ scores is likely to be biased by several fact, ors, such as gender, age, genetic background, latitude, and social habits. The objective of the present study was to determine the effect of different social synchronizers on the sleep/wake cycle of persons with different chronotypes. Volunteers were selected from a total of 1232 UFPR undergraduate students who completed the MEQ. Thirty-two subjects completed the study, including 8 morning types, 8 evening types and 16 intermediate types. Sleep schedules were recorded by actigraphy for 1 week on two occasions: during the school term and during vacation. Sleep onset and offset times, sleep duration, and mid-sleep time for each chronotype group were compared by the Mann-Whitney U-test separately for school term and vacation. School term and vacation data were compared by the Wilcoxon matched-pair test. Morning types showed earlier sleep times and longer sleep duration compared with evening types (23:00 ± 44 and 508.9 ± 50.27 vs 01:08 ± 61.95 and 456.44 ± 59.08, for the weekdays during vacation). During vacation, the subjects showed later sleep times, except for the morning types, who did not exhibit differences for sleep onset times. The results support the idea that social schedules have an impact on the expression of circadian rhythmicity but this impact depends on the individual chronotype.

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During adolescence, the sleep phase delay associated with early school times increases daytime sleepiness and reduces psychomotor performance. Some studies have shown an effect of gender on psychomotor performance in adults and children. Males present faster reaction times (RT) compared with females. The aim of the present study was to evaluate the influence of gender on Palm psychomotor vigilance task (PVT) performance in adolescents. Thirty-four adolescents (19 girls, 13 to 16 years old) attending morning school classes of a public school in Curitiba, PR, Brazil, participated in the study. Sleep patterns were measured using actigraphy and sleepiness data were accessed with the Karolinska Sleepiness Scale (KSS). KSS and PVT measurements were collected at two times in the morning (8:00 and 11:00 h). The data were compared using one-way ANOVA, considering gender as a factor. ANOVA indicated that gender did not affect sleep patterns and subjective somnolence; however, a statistically significant effect of gender was detected for PVT performance. Boys presented faster RT (RT-PVT1: 345.51 ms, F = 6.08, P < 0.05; RT-PVT2: 343.30 ms, F = 6.35, P < 0.05) and fewer lapses (lapses-PVT1: 8.71, F = 4.45, P < 0.05; lapses-PVT2: 7.82, F = 7.06, P < 0.05) compared with girls (RT-PVT1: 402.96; RT-PVT2: 415.70; lapses-PVT1: 16.33; lapses-PVT2: 17.80). These results showed that this effect of gender, already reported in adults and children, is also observed in adolescents. The influence of gender should be taken into account in studies that use Palm PVT to evaluate psychomotor performance in this age range.

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During adolescence, the sleep phase delay associated with early school times increases daytime sleepiness and reduces psychomotor performance. Some studies have shown an effect of gender on psychomotor performance in adults and children. Males present faster reaction times (RT) compared with females. The aim of the present study was to evaluate the influence of gender on Palm psychomotor vigilance task (PVT) performance in adolescents. Thirty-four adolescents (19 girls, 13 to 16 years old) attending morning school classes of a public school in Curitiba, PR, Brazil, participated in the study. Sleep patterns were measured using actigraphy and sleepiness data were accessed with the Karolinska Sleepiness Scale (KSS). KSS and PVT measurements were collected at two times in the morning (8:00 and 11:00 h). The data were compared using one-way ANOVA, considering gender as a factor. ANOVA indicated that gender did not affect sleep patterns and subjective somnolence; however, a statistically significant effect of gender was detected for PVT performance. Boys presented faster RT (RT-PVT1: 345.51 ms, F = 6.08, P < 0.05; RT-PVT2: 343.30 ms, F = 6.35, P < 0.05) and fewer lapses (lapses-PVT1: 8.71, F = 4.45, P < 0.05; lapses-PVT2: 7.82, F = 7.06, P < 0.05) compared with girls (RT-PVT1: 402.96; RT-PVT2: 415.70; lapses-PVT1: 16.33; lapses-PVT2: 17.80). These results showed that this effect of gender, already reported in adults and children, is also observed in adolescents. The influence of gender should be taken into account in studies that use Palm PVT to evaluate psychomotor performance in this age range.

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Recent studies suggest that short-sleep duration is independently associated with obesity in the general population. The population of truck drivers is of particular interest, because they frequently work irregular shifts that in turn are associated with short-sleep duration. In addition, truck drivers have a high prevalence of sedentary habits, poor diet, and obesity. The present study aimed at verifying the association between sleep patterns and factors associated with obesity in this population. The study sample consisted in 4,878 truck drivers who participated in a campaign promoted by a highway company in the State of São Paulo, Brazil. This campaign offered highway truck drivers a medical and laboratorial evaluation. The truck drivers completed a questionnaire concerning demographic data, sleep duration, consumption of medications, and medical problems, such as diabetes, cardiopathy, and hypertension; as well as the Berlin questionnaire, which is able to discriminate low and high risk for obstructive sleep apnea. Blood samples were collected to measure glucose and cholesterol levels. Also, body weight and height were registered to calculate the body mass index (BMI). The mean age (+/-SD) of the truck drivers studied was 40+/-10 years. Out of the truck drivers analyzed, 28.3% (n = 1,379) had a BMI > or =30.0 Kg/m2 (obesity). Among the 4,878 drivers included in the study, 1,199 (24.6%) were on medications and 334 (6.8%) were diabetic. Drivers (26.9%) with the greater BMI had a short sleep length. The independent factors associated with obesity were sleep duration <8 h/day (OR = 1.24), age >40 years (OR = 1.20), glucose levels >200 (OR = 2.02), cholesterol levels >240 (OR = 1.57), snoring (OR = 1.74), and hypertension (OR = 2.14). Smoking was not associated with obesity (OR = 0.69), and diabetes was considered a control variable. In conclusion, this study supports the hypothesis that short sleep duration as well as age >40 years are independently associated with obesity. This particular combination (short-sleep duration and obesity) is independently associated with several healthcare problems, including high levels of cholesterol, glucose, snoring, and hypertension. However, due to the cross-sectional nature of this study, no cause-effect relationship can be drawn from these results.

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The health issues that attract our attention when analyzing the truck driver population are the high prevalence of sedentary habits, inadequate diet, obesity, and proportion of hypertensive. All these are either considered risk factors for or a consequence of Obstructive Sleep Apnea (OSA). The objective of this study was to investigate the risk for OSA among 10,101 truck drivers and to correlate it with potentially related factors, such as serum glucose and cholesterol levels, smoking habits, alcohol and drug consumption, and self-reported physical activity. The drivers were invited to participate in the campaign "Saúde na Boléia" (Health Behind the Wheel) promoted by a Brazilian company responsible for the maintenance of approximately 360km of roads in the country. Drivers who spontaneously stopped at the campaign booths placed along the roads were invited to answer a questionnaire covering sociodemographic data such as age, alcohol, and drug consumption. All participants completed a Berlin Questionnaire and were classified as low- or high-risk subjects for OSA based on questions about snoring, tiredness during the day, and the presence of hypertension or obesity. Blood collection was accomplished at the same site by nurses and/or nursing students collaborating with the campaign for subsequent laboratory studies. Approximately 26% of the truck drivers were found to be at high-risk group for OSA. An adjusted multiple logistic model found the independent risk factors of smoking (OR=1.16; p=0.014) and drug use (OR= 1.32; p < 0.0001) were associated with high risk for OSA. The presence of self-reported occasional (OR=0.62; p<0.0001) and regular (OR=0.53; p < 0.0001) physical activity was found to be an independent factor protective of OSA. Educational programs, including ones aimed at improving one's health habits, such as engagement in physical exercise, should be considered in the development of initiatives to reduce the risk for OSA among the truck driver population.

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A recent worldwide trend in chemical and petrochemical industries is to extend the duration of shifts. Optimization of the labor force to reduce costs is one reason to increase the length of working time in a shift. Implementation of 12h shifts is a controversial decision for managers and scientists. Literature reviews show alertness is lower during the nighttime hours, and sleep duration is reduced and worse during the daytime. The main objective of this study was to evaluate the impacts of 12h shifts on alertness and sleep. To evaluate the duration and quality of sleep and alertness during work, 22 male shift workers on a continuous rotating schedule at a petrochemical plant completed activity logs and estimated alertness using analog 10-cm scales for 30 consecutive days, three times (at 2h, 6h, and 10h of the shift) every work shift. Statistical tests (analysis of variance [ANOVA] and Tukey) were performed to detect differences between workdays and off days. The shift schedule was 2 days/3 nights/4 off days, followed by 3 days/2 nights/5 off days, followed by 2 days/2 nights/5 off days. Sleep duration varied significantly (p < .001) among the work shifts and off days. Comparing work nights, the shortest mean sleep occurred after the second night (mean = 311.4 minutes, SD = 101.7 minutes), followed by the third night (mean = 335.3 minutes, SD = 151.2 minutes). All but one shift (sleep after the first work night) were significantly different from sleep after the first 2 workdays (p < .002). Tukey tests showed no significant differences in sleep quality between workdays and nights, with the exception of sleep after the third day compared to sleep after night shifts. However, significant differences were detected between off days and work nights (p < .01). ANOVA analysis showed borderline differences among perceived alertness during day shifts (p = .073) and significant differences among the hours of the shifts (p = .0005), especially when comparing the 2nd hour of the first day with the 10th hour of all the day shifts. There were no significant differences in perceived alertness during night work among the first, second, and third nights (p = .573), but there were significant differences comparing the times (2nd, 6th, 10th hour) of the night shifts (p < .001). The evaluation of sleep (duration and quality) and level of alertness have been extensively used in the literature as indicators of possible performance decrements at work. The results of this study show poorer sleep after and significantly decreased alertness during night work. Shifts of 12h are usually implemented for technical and economic reasons. These results point out the necessity of a careful trade-off between the financial and technical gains longer shifts might bring and the possible losses due to incidents or accidents from performance decrements during work.

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