Circadian hygiene, a concept not to be confused with the notion of public or social hygiene, should be discussed among experts and society. Light–dark cycles and other possible synchronizers of the human circadian timing system affect ways of life, including sleeping, eating, working and physical activity. Some of these behaviors have also been investigated individually as synchronizers (e.g., eating times). Therefore, the knowledge held today about circadian rhythms, and their implications for health, allows future perspectives in this field to be mapped. The present article summarizes the latest knowledge on factors influencing circadian rhythms to discuss a perspective for the future of health promotion based on circadian hygiene. However, it is important to highlight that circadian hygiene is the product of an imbrication of individual and societal involvement. First, it is important to adopt practices and devise public health policies in line with circadian hygiene. Second, individual healthy habits require internal rhythms to be examined. Last, the research agenda on circadian hygiene can be developed on a public as well as individual level, raising the question as to how much society is willing to embrace this change.

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 (MCTQ_shift) 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.

Poor sleep quality is associated with unhealthy dietary choices and worse body composition among night-shift workers and women during the climacteric period. This study aimed to evaluate the effect of exogenous melatonin administration on the dietary intake and body composition in healthcare workers exposed to fixed-shift work during the climacteric period. A phase II randomized, double-blind, placebo-controlled clinical trial of climacteric women working fixed morning, afternoon, or night shifts was conducted. Baseline data collection included sociodemographic information, sleep parameters, dietary intake, and body composition using bioelectrical impedance. Participants received either 0.3 mg of melatonin or a placebo for three months. Baseline total caloric and carbohydrate intake was higher among night-shift workers than afternoon-shift workers, though afternoon-shift workers a had higher body weight and fat percentage. Post-intervention, caloric intake differences dissipated due to reduced intake among night-shift workers and increased intake among afternoon-shift workers, independent of melatonin or placebo administration. However, differences in body composition persisted. Postmenopausal participants showed reduced fat mass, while premenopausal participants experienced an increase, regardless of intervention. The results suggest that physiological nighttime melatonin doses, administered on non-consecutive nights for three months, were ineffective for changing dietary intake or body composition.

Background: Shift work necessitates alterations in daily routines, which can be detrimental to workers’ health and may also influence the activity and rest patterns of their children. Aim: The aim of this study was to evaluate the concordance between activity and rest parameters of mothers and their children, according to the mothers’ work shift (day vs. night). Methods: Twelve mother–child dyads participated in this study, including six mothers working night shifts and six working day shifts. All mothers followed a 12/36 h rotating schedule (07:00–19:00 for day shifts; 19:00–07:00 for night shifts). Participants wore actigraphy devices for 10 consecutive days. Sleep and motor activity parameters were analyzed using the Bland–Altman method. Results: Analysis of the five least active hours (L5) revealed increased nocturnal activity among the night shift group. The period of the 10 most active hours (M10) suggested greater activity in the day shift group, with a smaller difference between mother and child in the day shift group. The relative amplitude (RA) in the night shift group was lower among mothers compared to the day group. Interdaily stability (IS) was lower, and intradaily variability (IV) was higher in the night shift group, suggesting more irregular activity patterns. Bedtime data showed greater variability in the night shift group, with night shift mothers typically going to bed later than their children—a pattern that was also observed for wake times. In the day shift group, total sleep time did not differ between mothers and children; however, in the night shift group, discrepancies increased proportionally with total sleep duration. Sleep efficiency was lower among mothers in both groups, but the difference between mother and child was more pronounced in the night shift group. Conclusions: Night shift work among mothers appears to negatively affect both their own and their children’s activity and sleep parameters when compared to those in the day shift group.