Abstract: PURPOSE OF REVIEW: To delineate the current state of evidence on the impact of night shift work on age at natural menopause. RECENT FINDINGS: The only direct evidence is from a single observational study, which indicates that women who work night shifts are at moderately higher risk for earlier menopause and that this risk is more pronounced among younger women. Underlying biological mechanisms have yet to be sufficiently substantiated. A long-held line of inquiry, most strongly propagated by the observed link between night shift work and female breast cancer, is the 'Light at Night' hypothesis, which suggests melatonin-mediated circadian disruption as a potential regulator of reproductive signaling in women. Supporting evidence is found from observations of changes in endogenous melatonin production among night working women or in response to light exposure, and corresponding changes in endogenous ovarian hormone levels and modulated menstrual patterns, among other indications of altered central ovulation-governing processes. Susceptibility to night shift work may be modified by chronotype. SUMMARY: This review summarizes the literature related to night work and ovulatory regulation in humans, prioritizing population-based evidence to provide motivation for the study of circadian disruption and night shift work as a regulator of menopausal timing.
Keywords: Human Health; Review; shift work; Menopause; women
Abstract: INTRODUCTION: Shift work sleep disorder (SWSD), also known as shift work disorder (SWD), is a circadian rhythm sleep disorder characterized by insomnia and/or excessive sleepiness, associated with a recurring work schedule that overlaps the usual time designated for sleeping. PURPOSE: This article aims to provide a narrative review of the pharmacological trials conducted on SWD in the last 5 years, to better address safety and health issues inherent to this disorder. METHODS: An electronic literature search was conducted using PubMed. All eligible randomized controlled trials (RCTs) and cross-over RCTs with employees undertaking shift work (including night shifts) were considered, yielding three articles. RESULTS: All three studies showed the efficacy of armodafinil in improving subjective and objective sleepiness, clinical conditions, and global functioning regardless of shift duration. Both performance and driving simulator performance tests administered during the night shift bore better results following armodafinil administration than after placebo. However, armodafinil only reduced subjective disability in individuals working more than 9 h; furthermore, even after armodafinil, alertness was reduced but not normalized. CONCLUSION: These studies underscore the importance of preventing and/or minimizing disturbances due to shift work. This may be achieved through various strategies, such as the employer's commitment to adopt ergonomic criteria in shift design and to implement work-environment interventions like controlled bright light. Health personnel is of pivotal importance to detect potential factors of intolerance to shift work or early symptoms of SWD. Additional and improved studies are needed to further evaluate the effectiveness and safety of both pharmacological and non-pharmacological interventions.
Abstract: Several novel animal studies have shown that intrauterine metabolic programming can be modified in the event of reduced melatonin synthesis during pregnancy, leading to glucose intolerance and insulin resistance in the offspring. It is therefore postulated that female night workers when pregnant may expose the offspring to unwanted health threats. This may be explained by the fact that melatonin is essential for regulating energy metabolism and can influence reproductive activity. Moreover, the circadian misalignment caused by shift work affects fertility and the fetus, increasing the risk of miscarriage, premature birth and low birth weight, phenomena observed in night workers. Thus, we hypothesize that light-induced melatonin suppression as a result of night work may alter intrauterine metabolic programming in pregnant women, potentially leading to metabolic disorders in their offspring.
Keywords: Human Health; Pregnancy; Melatonin; Melatonin synthesis; Circadian disruption; shift work
Abstract: Background: Substantial evidence now indicates that exposure to visible light at night can be linked to a wide spectrum of disorders ranging from obesity to cancer. More specifically, it has been shown that exposure to short wavelengths in the blue region at night is associated with adverse health effects, such as sleep problems.
Objectives: This study aimed at investigating if exposure to blue light emitted from common smartphones in an environment with dim light at night alters human reaction time.
Methods: Visual reaction time (VRT) of 267 male and female university students were recorded using a simple blind computer-assisted VRT test, respectively. Volunteer university students, who provided their informed consent were randomly divided to two groups of control (N = 126 students) and intervention (N = 141 students). All participants were asked to go to bed at 23:00. Participants in the intervention group were asked to use their smartphones from 23:00 to 24:00 (watching a natural life documentary movie for 60 minutes), while the control group only stayed in bed under low lighting condition, i.e. dim light. Before starting the experiment and after 60 minutes of smartphone use, reaction time was recorded in both groups.
Results: The mean reaction times in the intervention and the control groups before the experiment (23:00) did not show a statistically difference (P = 0.449). The reaction time in the intervention group significantly increased from 412.64 ± 105.60 msec at 23:00 to 441.66 ± 125.78 msec at 24:00 (P = 0.0368) while in the control group, there was no statistically significant difference between the mean reaction times at 23:00 and 24:00.
Conclusions: To the best of the author’s knowledge, this is the first study, which showed that exposure to blue-rich visible light emitted from widely used smartphones increases visual reaction time, which would eventually result in a delay in human responses to different hazards. These findings indicate that people, such as night shift or on call workers, who need to react to stresses rapidly should avoid using their smartphones in a dim light at night.
Objectives: This study aimed at investigating if exposure to blue light emitted from common smartphones in an environment with dim light at night alters human reaction time.
Methods: Visual reaction time (VRT) of 267 male and female university students were recorded using a simple blind computer-assisted VRT test, respectively. Volunteer university students, who provided their informed consent were randomly divided to two groups of control (N = 126 students) and intervention (N = 141 students). All participants were asked to go to bed at 23:00. Participants in the intervention group were asked to use their smartphones from 23:00 to 24:00 (watching a natural life documentary movie for 60 minutes), while the control group only stayed in bed under low lighting condition, i.e. dim light. Before starting the experiment and after 60 minutes of smartphone use, reaction time was recorded in both groups.
Results: The mean reaction times in the intervention and the control groups before the experiment (23:00) did not show a statistically difference (P = 0.449). The reaction time in the intervention group significantly increased from 412.64 ± 105.60 msec at 23:00 to 441.66 ± 125.78 msec at 24:00 (P = 0.0368) while in the control group, there was no statistically significant difference between the mean reaction times at 23:00 and 24:00.
Conclusions: To the best of the author’s knowledge, this is the first study, which showed that exposure to blue-rich visible light emitted from widely used smartphones increases visual reaction time, which would eventually result in a delay in human responses to different hazards. These findings indicate that people, such as night shift or on call workers, who need to react to stresses rapidly should avoid using their smartphones in a dim light at night.
Keywords: Human Health; Blue light; smartphone; Reaction Time; shift work
Abstract: Shift work that involves circadian disruption has been classified as probably carcinogenic to humans by the International Agency for Research on Cancer, although more recent epidemiological evidence is not consistent. Several mechanisms have been postulated to explain an association between night work and female breast cancer, but the most likely is suppression of the hormone melatonin by light exposure at night. Three articles recently published in this journal describe aspects of exposure to light during night work. These articles and other evidence suggest that nighttime light levels may not always be sufficient to affect melatonin production, which could in part explain the inconsistencies in the epidemiological data. There is need to improve the specificity and reliability of exposure assessments in future epidemiological studies of night shift workers.
Keywords: Commentary; Human Health; Cancer; Breast cancer; shift work