Impact of nocturnal duty on cardiometabolic health: Insights across professions

Abstract

This editorial explores the significant cardiometabolic outcomes of nocturnal sentry duty and its broader implications for other professions with overnight work. Highlighting the paradox of essential nighttime labor and its adverse physiological effects, we discuss how occupations like healthcare, hospitality, and emergency services are similarly affected. The study by Lin et al provides critical insights into these dynamics and lays the groundwork for understanding nocturnal duty’s multifaceted impact on human health.

Key Words: Nocturnal duty; Cardiometabolic health; Night shifts; Armed forces; Healthcare workers; Shift work; Circadian rhythm disruption

Core Tip: Nocturnal sentry duty impacts cardiometabolic health by disrupting circadian rhythms, inducing hormonal imbalances, and increasing cardiovascular risk. These effects extend to various professions, including healthcare workers, pharmacists, and hospitality staff, emphasizing the need for targeted interventions and policies to mitigate health risks associated with night shifts.

INTRODUCTION

Increased societal pressure for productivity and the refinement of the division of labor have altered shift work dynamics in modern society. The 6^th European Working Conditions Survey reported that nearly 21% of the working population in 2021 engaged in shift work, characterized by irregular schedules outside traditional daytime hours and categorized into daily, night, rotating, and hybrid variants[1,2]. Nighttime work became an indispensable component of many professions, including the armed forces, healthcare, hospitality, and emergency services. Despite its critical nature, nocturnal duty presents unique challenges to human physiology, predominantly by disrupting the circadian rhythm-a natural regulator of bodily functions. In this context, the innovative study by Lin et al[3] marks a pivotal contribution by examining the cardiometabolic characteristics of armed forces personnel, an understudied population, performing nocturnal sentry duty. Their findings underscore the need to reevaluate occupational health strategies for individuals engaged in such demanding schedules[3].

Lin et al[3] conducted a cross-sectional study involving armed forces personnel, comparing those with nocturnal sentry duties to their counterparts with daytime roles. The study revealed significant differences in cardiometabolic profiles, including elevated blood pressure, altered lipid levels, and increased markers of insulin resistance among nighttime workers. Knowing there is a paucity of literature assessing the impact of shift work on cardiovascular and metabolic profiles in military personnel and recognizing that these findings reflect broader concerns about shift work in many populations, the potential impact on public health requires urgent attention.

UNDERSTANDING THE PHYSIOLOGICAL IMPACTS OF CIRCADIAN RHYTHM DISRUPTION AND NOCTURNAL WORK

Sleep health is a global health concern given that circadian rhythm disturbances and night shift work have an impact on many aspects of our physiology, including mood and cognitive impairment, increased substance use risk[4,5], and elevated cancer risk (e.g., breast, prostate, and chronic lymphocytic leukemia)[6,7]. This discussion will focus on its effects on the cardiovascular system.

Metabolic disturbances and hormonal imbalance

The circadian rhythm orchestrates vital processes, including hormone secretion, metabolism, feeding behavior, blood pressure, and cardiovascular function[8]. Nighttime work can disrupt this rhythm, leading to the suppression of melatonin due to artificial light exposure[9]. Elevated cortisol levels resulting from stress and irregular schedules contribute to insulin resistance and visceral fat deposition[10]. Furthermore, disruption of leptin and ghrelin, the hormones controlling hunger and satiety, can lead to increased caloric intake and weight gain[11].

For instance, van de Langenberg et al[12] reported that healthcare workers who worked in nightshift schedules exhibited significant alterations in lipid and metabolic profiles, including less favorable lipid profiles, like elevated lipoprotein levels when compared to day worker. Likewise, Bahinipati et al[13] documented that night shift healthcare workers exhibited higher levels of pro-inflammatory markers, specifically hypersensitive C-reactive protein, along with significantly elevated waist circumference, fasting blood sugar, and triglycerides. Irwin[14] further observed that chronic sleep deprivation can upregulate pro-inflammatory cytokines and increase the risk of metabolic disorders. Moreover, Spiegel et al[15] found that partial sleep debt (four hours of sleep for four consecutive nights) impairs glucose metabolism and alters endocrinologic function, thereby increasing risk of metabolic syndrome.

Uniquely, Lin et al[3] investigated a cohort of military personnel performing brief night sentry duties (2-4 hours per shift, up to 5 times per month) and observed that even this relatively mild form sleep deprivation was associated with reduced high-density lipoprotein cholesterol (HDL-C) levels and an increased likelihood of impaired fasting glucose. This finding highlights the possibility that even short-term, infrequent disruptions in the sleep-wake cycle can adversely affect metabolic and cardiovascular health[3].

Of note, alterations in circadian rhythms can also drive differential gene expression, disrupting key intestinal clock genes involved in lipid absorption. This dysregulation leads to a lipid profile that elevates the risk of atherosclerosis and predisposes individuals to obesity and metabolic syndrome[16]. Additionally, Wirth et al[17], through an analysis of the National Health and Nutrition Examination Survey, demonstrated that night shift workers are more likely to adopt proinflammatory and obesogenic dietary patterns, further compounding their risk of metabolic and cardiovascular diseases.

Cardiovascular risks

Chronic circadian misalignment has been associated with an elevated risk of cardiovascular disease[10]. Disrupted sleep patterns and heightened stress levels contribute to increased blood pressure and impaired endothelial function, thereby potentially exacerbating the risk of atherosclerotic cardiovascular disease[18]. Extensive epidemiological evidence indicates that nocturnal workers exhibit a higher prevalence of hypertension, arrhythmias, and ischemic heart disease[19].

Recent evidence underscores the cardiovascular implications of shift work. Wang et al[20], utilizing data from a large-scale United Kingdom Biobank study, demonstrated that both current and cumulative lifetime exposure to night shifts were associated with an increased risk of atrial fibrillation and coronary heart disease, although no significant associations were observed for stroke or heart failure. Similarly, Kader et al[21] reported that permanent and frequent night shift schedules significantly elevated the risk of ischemic heart disease. Interestingly, frequent quick returns to work following afternoon shifts (defined as less than 11 hours between the end of an afternoon shift and the start of the next shift) were also linked to a higher incidence of ischemic heart disease, although no significant association with atrial fibrillation was identified[21]. These findings suggest that even minor disruptions to inter-shift recovery periods and sleep schedules can substantially impact individual cardiovascular risk profiles.

Night shift work may contribute to increased nocturnal blood pressure, which is itself a significant cardiovascular risk factor. A cross-sectional study of healthcare workers who worked at least six-night shifts per month revealed that disrupted sleep patterns could significantly reduce systolic and diastolic nocturnal dipping. This suggests that individuals working night shifts are more prone to hypertension and related comorbidities[22]. Non-dipping blood pressure has been associated with adverse cardiovascular events and heart failure in both hypertensive and general populations[23,24].

Nevertheless, Lin et al[3] demonstrated that even partial sleep deprivation associated with night shift work was correlated with higher resting pulse rates compared to non-shift workers. While systolic and diastolic blood pressures were not significantly affected, a higher resting pulse rate may reflect heightened sympathetic tone, an independent predictor of adverse cardiovascular outcomes and a critical contributor to the pathophysiology of hypertension[25].

EFFECT OF PARTIAL SLEEP DEPRIVATION ACROSS GENDERS

Lin et al[3] found that increased nighttime sentry duty was positively correlated with a higher pulse rate and a lower HDL-C level, independent of gender, as well as several other possible confounders. However, the role of gender as a possible effect modifier remains obscure. Moreover, performing interaction analyses and stepwise regressions would have illustrated the effect of gender on all the associations that were assessed. Several studies have assessed the impact of gender on the relationship between sleep deprivation and cardiometabolic risk factors; however, the results have been conflicting. For instance, in a cross-sectional study performed by Sabanayagam and Shankar[26], stratified analyses showed that short sleep duration was associated with an increased cardiovascular risk in both sexes, with the strength of these associations being significantly greater in women. Also, Fan et al[27] showed that among women, short sleep (< 7 hours/day) was significantly associated with higher odds of general and visceral obesity, suggesting that insufficient sleep may more adversely affect adiposity in females, while similar associations were not found in males. Moreover, Silva-Costa et al[28] found that in women, both self-reported short sleep duration and insomnia symptoms were linked to elevated odds of obesity, hypertension, and increased glycated hemoglobin levels. In contrast, among men, long sleep duration and insomnia symptoms were predominantly associated with hypertriglyceridemia, with no significant associations observed for obesity, hypertension, or glycated hemoglobin[28]. On the other hand, in another cross-sectional study, Kim et al[29] showed that short sleep (< 6 hours) was linked to metabolic syndrome and increased waist circumference in men, whereas in women it was only associated with increased waist circumference and with a lower magnitude of association.

The literature remains conflicted regarding the gender-specific impact of sleep deprivation on cardiometabolic risk factors. Further large-scale observational studies and randomized controlled trials are required to specifically decipher the role of gender in mediating these associations.

IMPACT ON VARIED PROFESSIONS

While Lin et al[3] study focused on the armed forces, similar challenges are faced by professionals in healthcare, hospitality, emergency services, and even logistics. Though there are known direct effects on an individual’s health, attention must also be paid for the indirect toll on those that rely on night shift workers’ services-such as hospital patients. Similarly, hospitality workers and pharmacists operating 24-hour establishments are exposed to chronic sleep deprivation and metabolic stress. These examples underline the universality of night shift-induced health issues, necessitating cross-industry interventions.

CALL FOR ACTION

The mounting evidence from Lin et al[3] and similar studies underline the significant public health concern regarding the cardiovascular and metabolic risks associated with nocturnal work. As the prevalence of shift work and nocturnal duties increases across various industries, it is imperative that governments, policymakers, healthcare professionals, and employers collaborate to implement evidence-based interventions.

Policy development for shift work regulation

Policymakers must prioritize the creation and enforcement of comprehensive policies to address the unique health risks associated with shift work, particularly nocturnal work. Governments should implement regulations limiting the duration of continuous nocturnal shifts to reduce the risk of prolonged circadian disruption. These regulations should be based on research regarding safe sleep thresholds and the cumulative effects of sleep deprivation. Additionally, policies should ensure that workers are entitled to adequate rest periods between shifts. These rest periods should be long enough to allow workers to recover physically and mentally, with a focus on aligning rest periods with circadian rhythms to minimize further disruption of sleep patterns. To further reduce the risks, employers should be encouraged to adopt flexible scheduling options that accommodate individual differences in sleep patterns. This flexibility can minimize circadian disruption and provide opportunities for restorative sleep, reducing long-term cardiovascular risks. Lastly, governments should establish limits on the number of consecutive night shifts workers can undertake, ensuring ample recovery time through alternating shift schedules and sufficient time off between shifts.

Workplace adaptations and health infrastructure

Employers should implement workplace interventions that promote physical and mental well-being for nocturnal workers. First, workplaces should provide health-conscious meal options to counteract the negative effects of irregular eating schedules, which can exacerbate metabolic disturbances and cardiovascular risks. Nutritional counseling should also be available to shift workers to guide their dietary choices. Additionally, work environments should be ergonomically designed to support workers’ physical well-being, reducing the risk of musculoskeletal strain and fatigue. Adjustable chairs, standing desks, and appropriate lighting are important elements to help workers maintain comfort and alertness throughout their shifts. Furthermore, employers should integrate structured short breaks into shift schedules to prevent fatigue and stress accumulation. These breaks, such as 10-15 minutes every 2-3 hours, would allow workers to rest, hydrate, and stretch, reducing cardiovascular strain and promoting mental alertness. Lastly, wellness programs focusing on physical and mental health should be integrated into the workplace. These programs can offer mental health counseling, sleep hygiene education, and stress management workshops to provide workers with the tools needed to combat the physiological and psychological toll of nocturnal work.

Awareness campaigns and training

Raising awareness about the risks of nocturnal work and promoting healthier behaviors are crucial steps toward improving the health of affected workers. Public health campaigns targeting nocturnal workers should educate them about the risks of sleep deprivation and circadian disruption. These campaigns should emphasize the importance of healthy lifestyle choices, such as nutrition, exercise, and sleep hygiene. Workers engaged in nocturnal duties should also receive training on sleep hygiene techniques, such as creating a conducive sleep environment, managing sleep-wake cycles, and using light exposure to optimize circadian rhythms. This education is critical in helping workers protect themselves from the cardiovascular risks associated with irregular sleep patterns. Stress management training should also be provided, offering tools such as mindfulness techniques, relaxation exercises, and coping strategies to reduce the negative impact of stress on cardiovascular health.

Integrating regular health screenings

To monitor the health of nocturnal workers and intervene early in cases of adverse health effects, regular health screenings should be integrated into the workplace. These screenings should assess cardiovascular risk factors, including blood pressure, cholesterol levels, blood glucose, and body mass index. Regular assessments will allow for early intervention and lifestyle modifications to mitigate health risks. Additionally, health screenings should include evaluations of sleep quality and mental health status. Workers showing signs of sleep disorders, depression, or anxiety should be referred to healthcare professionals. Policymakers should also allocate funding for studies to identify biomarkers associated with cardiovascular disease and metabolic disorders caused by nocturnal work. These biomarkers would allow for the early detection of workers at risk, providing actionable insights into when an individual’s sleep deficit surpasses a safe level and warrants intervention.

Research on sleep deprivation, circadian disruption, and cardiovascular risk factors

Despite the increasing body of evidence showing the detrimental effects of nocturnal work on cardiovascular and metabolic health, significant gaps remain in understanding the full extent of these risks. To address this, research must be prioritized in the following areas. First, studies should focus on establishing the threshold of sleep deprivation beyond which cardiovascular risk significantly increases. This would help create more precise regulations and personalized health recommendations for shift workers. There is also an urgent need to identify biomarkers that accurately reflect the impact of sleep disruption on cardiovascular health and metabolism. Research should explore markers of sympathetic activation, inflammation, and metabolic abnormalities. Longitudinal studies should be conducted to assess the cumulative effects of nocturnal work on cardiovascular health, taking into account the effects of sleep deprivation, circadian disruption, and shift work history.

Collaborative efforts across stakeholders

To reduce the cardiovascular burden of shift work, collaboration between policymakers, employers, healthcare providers, and researchers is essential. By working together, these stakeholders can implement evidence-based interventions that protect the health of nocturnal workers and promote sustainable, healthier work environments. Policymakers should create regulatory frameworks and provide incentives for employers to adopt health-conscious work practices. Employers must prioritize worker well-being alongside productivity, integrating health initiatives and accommodations into their operational practices. Healthcare professionals should provide education and guidance to workers on managing cardiovascular risks associated with nocturnal duties. Researchers should focus on addressing the remaining gaps in the literature, particularly in establishing biomarkers and safe sleep thresholds for nocturnal workers.

ESSENTIAL SLEEP STRATEGIES FOR NIGHT SHIFT WORKERS

To optimize sleep and minimize the negative effects of night shifts, workers must prioritize sleep and avoid accumulating “sleep debt”. Instead of taking on additional chores or responsibilities after a shift, sleep should be the primary focus. Workers should head to bed early and allow enough time to rest, as it may take a few days to fully recover from sleep deprivation. It’s essential not to fall behind on sleep. Sleeping as long as possible after a shift is important since night shift workers often get less and poorer-quality rest than those working the day shift. Additionally, taking a quick nap 1.5 to 3 hours before a night shift can improve alertness and extend total sleep time[30].

Light exposure plays a critical role in regulating the circadian rhythm, so workers should spend time in brightly lit areas during the early part of the day to boost energy levels. As the shift nears its end, workers must reduce light exposure to help transition into sleep. Wearing blue-light-blocking glasses before heading home can also assist in adjusting the body’s internal clock. Once home, workers should go directly to bed to avoid disrupting their sleep cycle. A light snack, such as Greek yogurt or eggs with toast, rich in protein and carbs, should be consumed before sleep to enhance sleep quality[30].

To maximize daytime rest, workers must ensure that their bedroom is as dark as possible, blocking out any natural daylight. Family and friends should be asked to respect the sleep schedule and minimize disturbances. If sleep problems persist, melatonin supplements may be considered to help regulate the sleep-wake cycle, though it is important to consult with a doctor beforehand. By following these strategies, workers can improve both the quality and quantity of their sleep, reducing the risks associated with nocturnal work[30].

CONCLUSION

The critical insights provided by Lin et al[3] emphasize the substantial health risks associated with nocturnal sentry duty. While the study focused on armed forces personnel, its implications extend to other professions requiring overnight work, including healthcare workers, restaurant staff, and emergency responders. Addressing these challenges requires a collaborative effort among researchers, policymakers, and employers to safeguard the health and well-being of nocturnal workers. By prioritizing health equity in occupational settings, we can mitigate the cardiometabolic burden imposed by night shifts and improve long-term outcomes for affected populations.