BackgroundCircadian system time cues (zeitgebers) acting synergistically at the right times can foster chronobiological homeostasis and ultimately health. Modern 24/7 societies are challenging chronobiological homeostasis and public health. Exercise has been discussed as a potential zeitgeber for the human circadian system. Thus, if timed correctly, exercise may help in maintenance of chronobiological homeostasis and foster public health amidst increasingly challenging 24/7 lifestyles.ObjectiveTo test, using a systematic review of the literature, the following hypothesis: exercise is a zeitgeber for the human circadian system.Data sourcesThe PubMed database was systematically searched on 19 October 2017 for relevant scientific studies and reports concerning chronobiology and exercise. Eligibility criteria were defined to include articles considering exercise as a potential zeitgeber for human circadian rhythmicity or chronobiological effects of exercise on health and/or physical performance. Cognitive effects and effects on children were excluded from the synthesis.ResultsOur systematic literature search and synthesis is compatible with the validity of the hypothesis. We report that potential exercise-zeitgeber properties may be used to improve health and performance.ConclusionsInformed timing of exercise, specific to the circadian rhythm phase and zeitgeber exposure of the individual, must be advocated in performance and disease contexts as an adjunct therapeutic or preventative strategy and physical enhancer.

ObjectiveThe COVID-19 pandemic is demanding for occupational medicine and for public health. As healthcare workers (HCWs) fight impacts of SARS-CoV-2 on front lines, we must create safe work environments through comprehensive risk assessments, evaluation and effective implementation of counter-measures. We ask: ‘What does current literature report on health risks at workplaces regarding COVID-19?’ and ‘What do current studies report on the effectiveness of enacted preventative recommendations?’MethodsAs a snapshot of early HCW research, on 26 April 2020, we conducted a rapid systematic literature search in three databases (PubMed, Web of Science and PsycInfo) for COVID-19-related health outcomes and preventive measures in healthcare-associated workplaces.Results27 studies were identified as relevant for exploring the risk of infection, 11 studies evaluated preventive measures. The studies described that SARS-CoV-2 impacts significantly on HCW’s health and well-being, not only through infections (n=6), but also from a mental health perspective (n=16). 4 studies reported indirect risks such as skin injuries, one study described headaches to result from the use of personal protective equipment. Few studies provided information on the effectiveness of prevention strategies. Overall, most studies on health risks as well as on the effectiveness of preventive measures were of a moderate-to-low quality; this was mainly due to limitations in study design, imprecise exposure and outcome assessments.ConclusionsDue to widespread exposure of HCW to SARS-CoV-2, workplaces in healthcare must be as safe as possible. Information from HCW can provide valuable insights into how infections spread, into direct and indirect health effects and into how effectively counter-measures mitigate adverse health outcomes. However, available research disallows to judge which counter-measure(s) of a current ‘mix’ should be prioritised for HCW. To arrive at evidence-based cost-effective prevention strategies, more well-conceived studies on the effectiveness of counter-measures are needed.

Analysis 2.1. Comparison 2 Bright light alone at night versus normal light (300 lux) plus placebo capsule, Outcome 1 Sleepiness during the night shift (5-min. Reaction Time Test -milliseconds). . . . . . . . . . . . . Analysis 2.2. Comparison 2 Bright light alone at night versus normal light (300 lux) plus placebo capsule, Outcome 2 Total sleep time, next day

not accurately reflect what constitutes satisfying sex in this population, yielding falsely low scores. Women who reported greater importance of sex had higher maintenance of sexual activity. In contrast, we found that sexual function, as measured by the FSFI, is not associated with maintenance of sexual activity. This suggests that the "quality" of sex does not affect whether a woman will continue to have sex over time. Midlife women have many reasons for engaging in sex that go beyond "quality." These findings challenge prior assumptions about female sexual function in midlife. As we study and care for these women, a more nuanced understanding of female sexuality is essential.

Sleep and its impact on physiology and pathophysiology are researched at an accelerating pace and from many different angles. Experiments provide evidence for chronobiologically plausible links between chronodisruption and sleep and circadian rhythm disruption (SCRD), on the one hand, and the development of cancer, on the other. Epidemiological evidence from cancer incidence among some 1 500 000 study individuals in 13 countries regarding associations with sleep duration, napping or "poor sleep" is variable and inconclusive. Combined adjusted relative risks (meta-RRs) for female breast cancer, based on heterogeneous data, were 1.01 (95% CI: 0.97-1.06). Meta-RRs for cancers of the colorectum and of the lung in women and men and for prostate cancer were 1.08 (95% CI: 1.03-1.13), 1.11 (95% CI: 1.00-1.22) and 1.05 (95% CI: 0.83-1.33), respectively. The significantly increased meta-RRs for colorectal cancer, based on homogeneous data, warrant targeted study. However, the paramount epidemiological problem inhibiting valid conclusions about the associations between sleep and cancer is the probable misclassification of the exposures to facets of sleep over time. Regarding the inevitable conclusion that more research is needed to answer How are sleep and cancer linked in humans? we offer eight sets of recommendations for future studies which must take note of the complexity of multidirectional relationships.