High social jetlag is correlated with nocturnal inhibition of melatonin production among night workers.

Night work can lead to social jetlag (SJL), which can be briefly defined as the difference between social and biological time. In this sense, SJL has been viewed as a proxy for circadian misalignment. Studies have suggested that SJL may modify physiological processes, such as blood pressure, glucose metabolism, cortisol, and melatonin production. Therefore, we aimed to verify the correlation between SJL and nocturnal inhibition of melatonin production estimated by the concentration of its urinary metabolite (6-sulfatoximelatonin). The study included day workers (n = 9) and night workers (n = 13) from a public maternity hospital in the city of São Paulo. A questionnaire was used to obtain sociodemographic data, life habits, working conditions, and the Munich Chronotype Questionnaire (MCTQshift) was used to assess chronotype. Urine was collected on workdays and days off to estimate the concentration of 6-sulfatoximelatonin (aMT6s), quantified by the ELISA method. We found SJL 13 times higher for night workers (10.6 h) than day workers (0.8 h). The excretion of aMT6s in night workers was statistically different on workdays as opposed to days off, with the lowest excretion on workdays, as expected. SJL was correlated with the aMT6s's delta between the night off and night on among night workers, indicating that the higher is the SJL, the lower is the melatonin production. As expected, social jetlag was higher among night workers, compared to day workers. Moreover, our findings showed that melatonin concentration is directly correlated with SJL.

Shift work and endocrine disorders.

The objective of this review was to investigate the impact of shift and night work on metabolic processes and the role of alterations in the sleep-wake cycle and feeding times and environmental changes in the occurrence of metabolic disorders. The literature review was performed by searching three electronic databases for relevant studies published in the last 10 years. The methodological quality of each study was assessed, and best-evidence synthesis was applied to draw conclusions. The literature has shown changes in concentrations of melatonin, cortisol, ghrelin, and leptin among shift workers. Melatonin has been implicated for its role in the synthesis and action of insulin. The action of this hormone also regulates the expression of transporter glucose type 4 or triggers phosphorylation of the insulin receptor. Therefore, a reduction in melatonin can be associated with an increase in insulin resistance and a propensity for the development of diabetes. Moreover, shift work can negatively affect sleep and contribute to sedentarism, unhealthy eating habits, and stress. Recent studies on metabolic processes have increasingly revealed their complexity. Physiological changes induced in workers who invert their activity-rest cycle to fulfill work hours include disruptions in metabolic processes.

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.