Chronotype is a reliable biomarker for studying the influence of external zeitgebers on circadian entrainment. Assessment of chronotype variation in participants exposed to extreme photoperiods may be useful to investigate how changes in light–dark cycle modulate the circadian system. This study aimed to examine chronotype and sleep changes during a winter campaign at the Argentine Antarctic station Belgrano II. A sample of 82 men who overwintered in Antarctica completed the Munich Chronotype Questionnaire during March (daylight length: 18.6 h), May (daylight length: 2.8 h), July (daylight length: 0 h), September (daylight length: 14.5 h), November (daylight length: 24 h). The main results showed a decrease in sleep duration and a delay in chronotype and social jetlag during the polar night, highlighting the influence of social cues and the impact of the lack of natural light on circadian rhythms.

Background: The main objective of this study was to describe the relationship between working conditions, sleep and psycho-affective variables and medical errors. Methods: This was an observational, analytical and cross-sectional study in which 661 medical residents answered questionnaires about working conditions, sleep and psycho-affective variables. Actigraphic sleep parameters and peripheral temperature circadian rhythm were measured in a subgroup of 38 subjects. Bivariate and multivariate predictors of medical errors were assessed. Results: Medical residents reported working 66.2 ± 21.9 weekly hours. The longest continuous shift was of 28.4 ± 10.9 h. They reported sleeping 6.1 ± 1.6 h per day, with a sleep debt of 94 ± 129 min in workdays. A high percentage of them reported symptoms related to psycho-affective disorders. The longest continuous shift duration (OR = 1.03 [95% CI, 1.00–1.05], p = 0.01), working more than six monthly on-call shifts (OR = 1.87 [95% CI, 1.16–3.02], p = 0.01) and sleeping less than six hours per working day (OR = 1.66 [95% CI, 1.10–2.51], p = 0.02) were independently associated with self-reported medical errors. The report of medical errors was associated with an increase in the percentage of diurnal sleep (2.2% [95% CI, 0.1–4.3] vs 14.5% [95% CI, 5.9–23.0]; p = 0.01) in the actigraphic recording. Conclusions: Medical residents have a high working hour load that affect their sleep opportunities, circadian rhythms and psycho-affective health, which are also related to the report of medical errors. These results highlight the importance of implementing multidimensional strategies to improve medical trainees’ sleep and wellbeing, increasing in turn their own and patients’ safety.

A circadian disruption, manifested by disturbed sleep and low-grade inflammation, is commonly seen in cardiovascular diseases (CVDs). The decline in plasma melatonin, which is a conserved phylogenetic molecule across all known aerobic creatures, is also a common feature in CVDs. The daily evening pineal melatonin surge synchronizes both the central pacemaker located in the hypothalamic suprachiasmatic nuclei and myriads of cellular clocks in the periphery (“chronobiotic effect”). Melatonin also has cytoprotective properties, acting primarily not only as an antioxidant by buffering free radicals but also by regulating inflammation. In CVDs, exogenous melatonin administration decreases nocturnal hypertension, improves systolic and diastolic blood pressure, reduces the pulsatility index in the internal carotid artery, decreases platelet aggregation, and reduces serum catecholamine levels. Melatonin evokes an increase in parasympathetic activity in the heart. Allometric calculations based on animal research show that melatonin’s cytoprotective benefits in CVDs may require high doses to be fully manifested (in the 100–200 mg/day range). If melatonin is expected to improve health in CVDs, the low doses currently used in clinical trials (i.e., 2–10 mg) are presumably insufficient.

Background. Although melatonin is widely used in Sleep Medicine for its chronobiological action, its potent antioxidant and mitochondrial regulatory effects, as well as its immunomodulatory and anti-inflammatory functions, make it of interest as a cytoprotective agent in several chronic pathologies. These actions are evident at doses higher than those used for sleep disorders. Even at high doses, melatonin’s adverse effects are few, mild, and self-limited or resolve quickly after discontinuation of treatment. Based on its safety profile, we treated melatonin for sleep disorders in the presence of comorbidities with doses ≥ 40 mg daily. Methods. This was a retrospective mixed observational analytical design comprising a retrospective uncontrolled cohort analysis and a cross-sectional study. Eighty-one patients (57 female) with sleep disorders ranging in age from 55 to 98 years (mean 74.4 years) were treated with melatonin 40 to 200 mg daily (mean 72.7 mg) were examined. Fifty-six percent of patients received treatment for more than 4 years. The control group for the cross-sectional analysis included 81 patients over 52 years of age, matched by age and sex and not receiving melatonin but having sleep disorders within the same period. Results. A significant decrease was observed in arterial hypertension, ischemic heart disease and diabetes mellitus after melatonin administration. Analysis of clinical laboratory variables indicated no changes in the treated group versus the untreated group, except for a lower alkaline phosphatase concentration in patients who received melatonin. Conclusions. These findings suggest a beneficial effect of cytoprotective doses of melatonin on the cardiovascular and metabolic profile in an aged population.

We compared three different work schedules in a large oil company: 1) two days of 12 h of daytime shifts followed by two consecutive 12 h night shifts, followed by four work-free days (“2 x 2 x 4”), 2) four consecutive 12 h daytime shifts and four consecutive 12 h night shifts, flanked by four work-free days (“4 x 4 x 4”), 3) a non-rotating schedule involving continuous 12 h daytime shifts during 40 days (“fixed 12 h”). We measured wrist-actigraphy, peripheral temperature rhythms, and subjective self-reports regarding fatigue, somnolence, and psycho-affective features. Sleep duration on the resting period was significantly less than the recommended 7 h. The “2 x 2 x 4” schedule resulted in decreased sleep regularity and increased circadian disruption, higher levels of insomnia, increased fatigue impact, lower alertness levels, and heightened symptoms of depression associated with more nocturnal sleep time after diurnal work. Our findings indicate that health and safety vary depending on the type of schedule employed.