Sleep and circadian rhythms are closely interconnected physiological processes that regulate metabolic, endocrine, cardiovascular, and behavioural functions. The human circadian system promotes wakefulness and metabolic activity during the biological day and sleep during the biological night. Healthcare professionals working night and rotating duties are frequently required to reverse this normal pattern, remaining awake during the biological night and attempting to sleep during the daytime.[1,2]. Such occupational schedules may produce two related but distinct problems: sleep deprivation and circadian misalignment. Sleep deprivation occurs when individuals obtain insufficient total sleep, whereas circadian misalignment arises when sleep, wakefulness, activity, or food intake occurs at a biological time that conflicts with the endogenous circadian system.[2,3] Shift workers frequently experience both conditions simultaneously. Daytime sleep following a night duty may be shorter and more fragmented because environmental light, noise, family responsibilities, and social activities favour wakefulness. Night workers may therefore experience chronic reductions in total sleep time, frequent awakenings, non-restorative sleep, and excessive daytime sleepiness. These disturbances may persist or become more severe with repeated night duties and rotating schedules. Sleep restriction has important metabolic consequences. Experimental studies have demonstrated that insufficient sleep can reduce insulin sensitivity, impair glucose tolerance, alter appetite-regulating hormones, increase sympathetic activity, and influence energy balance.[1-3] Circadian misalignment itself can further impair metabolic regulation even when sleep duration is partly controlled. The association between sleep disturbance and metabolic syndrome is particularly relevant because metabolic syndrome comprises a cluster of central obesity, abnormal glucose metabolism, elevated blood pressure, hypertriglyceridaemia, and reduced high-density lipoprotein cholesterol. Each of these abnormalities may potentially be influenced by sleep loss or circadian disruption. Healthcare workers constitute a vulnerable occupational group. Hospitals require continuous staffing and therefore depend on night duties and rotating schedules among doctors, residents, nurses, technicians, laboratory personnel, pharmacists, emergency staff, and other employees. In addition to altered sleep schedules, healthcare professionals may experience prolonged duties, emergency workloads, occupational stress, irregular meals, high caffeine intake, and limited opportunities for physical activity. The type of shift schedule may also influence circadian disruption. Fixed night workers may partially adapt to a repeated schedule, whereas rotating shift workers repeatedly alternate between day and night duties. Such changes can prevent stable circadian adaptation and may produce recurrent internal desynchronization. Duration of shift-work exposure is another potentially important factor. Repeated circadian disruption over several years may contribute to cumulative metabolic risk through persistent abnormalities in sleep, appetite, glucose regulation, adiposity, blood pressure, and lipid metabolism. Recent systematic-review evidence has emphasized the relationship between shift work, disturbed sleep, and metabolic syndrome. The available evidence suggests that reduced sleep quantity may be particularly important and that longer night-shift exposure may be associated with increasing metabolic risk. The present study was therefore designed to assess sleep disturbances among healthcare professionals working different occupational schedules and to evaluate their relationship with metabolic syndrome. Particular attention was given to sleep duration, sleep quality, type of shift, duration of shift-work exposure, and cumulative occupational characteristics. Aim: To evaluate the relationship between sleep disturbances, shift-work exposure, and metabolic syndrome among healthcare professionals employed at a tertiary care teaching centre.

Study Design The study was designed as an observational analytical investigation of sleep, occupational shift exposure, and metabolic health among healthcare workers at a tertiary care teaching centre. Study Setting The study setting was a tertiary care teaching hospital providing continuous 24-hour healthcare services. The workforce included employees performing conventional daytime duties as well as fixed night and rotating shift schedules. Study Participants A total of 200 healthcare workers were represented in the illustrative analysis. Participants were classified as: • Daytime workers: 100 • Shift workers: 100 Among the 100 shift workers: • Fixed night-shift workers: 35 • Rotating shift workers: 65 The mean duration of shift-work exposure among shift workers was 5.6±3.2 years, and the mean frequency of night duties was 7.4±2.8 per month. Occupational Assessment Information regarding work schedules included: • Current occupational category • Type of work schedule • Duration of employment • Duration of shift-work exposure • Number of night duties per month • Consecutive night duties • Frequency of rotation • Total years of night-shift exposure Where feasible, occupational schedules were intended to be verified using departmental duty rosters. Sleep Assessment Participants were assessed for average sleep duration on work and non-work days. Information was also collected regarding: • Short sleep duration • Subjective sleep quality • Difficulty initiating or maintaining sleep • Frequent night awakening • Non-restorative sleep • Excessive daytime sleepiness • Sleep medication use • Variability between work-day and non-work-day sleep timing A validated instrument such as the Pittsburgh Sleep Quality Index could be used according to the final approved protocol. The source protocol defines a PSQI global score >5 as poor sleep quality. Metabolic Assessment Anthropometric measurements included body weight, height, BMI, and waist circumference. Blood pressure was assessed after adequate rest using standardized measurement procedures. Fasting biochemical investigations included: • Fasting plasma glucose • HbA1c • Total cholesterol • Triglycerides • HDL cholesterol • LDL cholesterol Metabolic Syndrome Metabolic syndrome was defined using predefined internationally recognized criteria based on the presence of at least three relevant abnormalities. The protocol specified the following components: • Waist circumference ≥90 cm in men or ≥80 cm in women • Triglycerides ≥150 mg/dL • HDL cholesterol <40 mg/dL in men or <50 mg/dL in women • Blood pressure ≥130/85 mmHg • Fasting glucose ≥100 mg/dL Statistical Analysis Continuous variables were expressed as mean±standard deviation or other appropriate descriptive statistics. Categorical variables were presented as frequency and percentage. Sleep characteristics were compared between daytime and shift workers. Metabolic-syndrome prevalence was evaluated according to work schedule, type of shift, duration of shift exposure, and sleep duration. Correlation analysis was planned for cumulative shift exposure and metabolic parameters. Multivariable logistic regression could be used to assess independent predictors of metabolic syndrome after adjustment for age, sex, BMI, physical activity, dietary pattern, smoking, and sleep duration. A p-value <0.05 was considered statistically significant. Ethical Considerations Institutional Ethics Committee approval and written informed consent were required before participant recruitment. Participant information was to be coded and maintained confidentially.

A total of 200 healthcare workers were represented, including equal numbers of daytime and shift workers. Among shift workers, 65% followed rotating schedules and 35% fixed night schedules. Table 1. Sleep characteristics among daytime and shift workers Sleep parameter Day workers (n=100) Shift workers (n=100) Mean sleep duration (hours) 7.0 ± 0.8 5.9 ± 1.0 Sleep duration <6 hours 14 (14.0%) 42 (42.0%) Poor sleep quality 27 (27.0%) 58 (58.0%) Frequent night awakening 18 (18.0%) 39 (39.0%) Excessive daytime sleepiness 21 (21.0%) 47 (47.0%) Shift workers exhibited considerably greater sleep disturbance than daytime workers. Average sleep duration was approximately 1.1 hours shorter among shift workers. Short sleep, poor subjective sleep quality, frequent awakening, and daytime sleepiness were all more common in the shift-work group. Table 2. Metabolic syndrome according to type and duration of shift work Shift characteristic Metabolic syndrome present n (%) Metabolic syndrome absent n (%) Fixed night shift 10 (28.6) 25 (71.4) Rotating shift 28 (43.1) 37 (56.9) <3 years shift exposure 5 (16.7) 25 (83.3) 3–5 years 9 (31.0) 20 (69.0) 6–10 years 14 (42.4) 19 (57.6) >10 years 10 (45.5) 12 (54.5) Metabolic syndrome appeared more common among rotating shift workers than fixed night workers. A progressive increase was also observed with duration of shift exposure, from 16.7% among those with less than three years of exposure to 45.5% among those exposed for more than ten years. Table 3. Association between sleep duration and metabolic syndrome Average sleep duration Metabolic syndrome n (%) No metabolic syndrome n (%) <6 hours 28 (45.2) 34 (54.8) 6–<7 hours 20 (32.3) 42 (67.7) ≥7 hours 8 (18.8) 34 (81.2) A clear gradient was observed in the illustrative data. Metabolic syndrome was most frequent among individuals sleeping less than six hours and least frequent among those reporting at least seven hours of sleep. Table 4. Illustrative predictors of metabolic syndrome Predictor Adjusted OR 95% CI p-value Shift work 2.41 1.35–4.31 0.003 Age 1.04 1.01–1.07 0.011 BMI 1.16 1.08–1.25 <0.001 Sleep duration <6 hours 1.72 1.01–2.94 0.046 Low physical activity 1.48 0.89–2.46 0.128 Unhealthy dietary pattern 1.63 0.97–2.75 0.065 In the illustrative regression model, both shift work and short sleep duration remained associated with metabolic syndrome after accounting for selected covariates. BMI and age were also independently associated with metabolic syndrome.

The present study evaluated sleep disturbance and occupational shift exposure in relation to metabolic syndrome among healthcare professionals. The illustrative findings showed substantial differences in sleep characteristics between daytime and shift workers and suggested that shorter sleep duration, rotating schedules, and longer cumulative shift exposure may be associated with increased metabolic risk. Shift workers reported an average sleep duration of 5.9 hours compared with 7.0 hours among daytime workers. Furthermore, 42% of shift workers slept for less than six hours, compared with 14% of daytime workers. This difference is clinically important because insufficient sleep has been associated with disturbances in glucose metabolism, appetite regulation, sympathetic activity, and energy balance.[1-3] The prevalence of poor sleep quality was also markedly higher among shift workers. More than half of shift workers reported poor subjective sleep quality compared with approximately one-quarter of daytime workers. Frequent awakening and excessive daytime sleepiness showed similar patterns. These differences are physiologically plausible. Night workers are required to remain awake during the biological night, when endogenous melatonin secretion and circadian sleep propensity are high. They subsequently attempt to sleep during daytime hours, when environmental light and the endogenous circadian alerting signal favour wakefulness. Daytime noise, social obligations, and domestic responsibilities may further fragment sleep.[2] Recent evidence has emphasized the relationship between sleep disturbance and metabolic health among shift workers. The systematic review cited in the source protocol by Park and Wegener examined 15 studies involving 37,147 participants and reported a consistent relationship between shift work, sleep disturbances, and metabolic syndrome. Importantly, the review suggested that reduced sleep quantity might demonstrate a stronger relationship with metabolic syndrome than subjective sleep quality. This observation is consistent with the illustrative findings of the present study. Metabolic syndrome occurred in 45.2% of participants sleeping less than six hours, compared with 18.8% of those sleeping seven hours or more. Participants sleeping between six and seven hours demonstrated an intermediate prevalence of 32.3%, suggesting a possible graded relationship between sleep duration and metabolic risk. Several mechanisms may explain this association. Experimental sleep restriction can impair insulin sensitivity and glucose tolerance and may alter leptin and ghrelin signalling, increasing hunger and energy intake. Short sleep may also increase sympathetic nervous-system activity, influence cortisol secretion, and reduce opportunities for physical recovery.[2,3] Sleep restriction may operate both independently and as a mediator of the relationship between shift work and metabolic syndrome. Night workers frequently obtain insufficient sleep because of biologically inappropriate sleep timing, while the circadian misalignment generated by the work schedule may independently influence metabolic regulation. The illustrative regression analysis supports this interpretation. Shift work remained associated with metabolic syndrome after adjustment for selected factors, while sleep duration below six hours also demonstrated an independent association. Although these values cannot be treated as definitive until verified using actual study data, the pattern suggests that both occupational schedule and insufficient sleep warrant consideration. Type of shift work may also influence metabolic health. In the illustrative results, metabolic syndrome was present in 43.1% of rotating shift workers compared with 28.6% of fixed night workers. Rotating shift schedules require repeated transitions between daytime and nighttime activity and may therefore prevent stable circadian adaptation. The central and peripheral circadian clocks respond to different environmental and behavioural cues. The central pacemaker is particularly sensitive to light, while peripheral clocks in the liver, pancreas, skeletal muscle, and adipose tissue respond strongly to feeding and activity. Repeated changes in sleeping and eating schedules may therefore generate internal desynchronization among physiological systems. However, the observation that rotating schedules appeared more adverse should be interpreted cautiously. Different rotating schedules may vary greatly in rotation speed, direction, number of consecutive nights, recovery intervals, and workload. Fixed night workers may also experience substantial circadian disruption, particularly when they return to daytime schedules during days off. Another important finding was the apparent relationship between duration of shift-work exposure and metabolic syndrome. In the illustrative dataset, metabolic-syndrome prevalence increased progressively from 16.7% among participants exposed for less than three years to 45.5% among those working shifts for more than ten years. This pattern suggests that cumulative exposure may be relevant. Repeated night work over many years could produce recurrent sleep restriction, altered food timing, chronic circadian misalignment, reduced physical activity, and progressive changes in body composition and glucose metabolism. The source protocol further demonstrated positive correlations between duration of shift work and BMI, waist circumference, fasting glucose, triglycerides, and systolic blood pressure. The strongest correlation was with waist circumference. Such findings suggest that prolonged occupational exposure might contribute to a gradual accumulation of metabolic abnormalities. Central adiposity may represent an especially important link. Sleep restriction and circadian disruption can influence appetite and energy balance, while visceral adiposity itself promotes insulin resistance and dyslipidaemia. Over time, these processes may contribute to the clustering of metabolic abnormalities characteristic of metabolic syndrome. Healthcare workers deserve particular attention because night work cannot simply be eliminated. Twenty-four-hour patient care requires continuous staffing. Therefore, interventions should focus on reducing unnecessary circadian disruption while preserving safe clinical services. Possible strategies include limiting excessive consecutive night shifts, providing adequate recovery periods between duties, considering more predictable rotation schedules, protecting opportunities for sleep, and educating staff regarding sleep hygiene. Dietary and behavioural factors should also be addressed. Night workers may have limited access to healthy meals and may depend on refined carbohydrates, processed foods, caffeinated beverages, and snacks during night duty. Appropriate access to nutritious food and advice regarding meal timing may therefore complement sleep interventions. Periodic occupational-health screening could be particularly valuable for long-term shift workers. Monitoring body weight, waist circumference, blood pressure, fasting glucose, HbA1c, and lipid profile may identify metabolic abnormalities before progression to overt diabetes or cardiovascular disease.

Shift-working healthcare professionals demonstrated substantially greater sleep disturbance than daytime workers in the illustrative analysis. Short sleep duration, poor sleep quality, frequent awakening, and excessive daytime sleepiness were all more common among shift workers. Metabolic syndrome appeared more frequent among rotating shift workers, participants with longer cumulative shift-work exposure, and those obtaining less than six hours of sleep. The illustrative multivariable analysis further suggested that both shift work and short sleep duration may contribute independently to metabolic risk. These findings support the inclusion of sleep and circadian health within occupational-health programmes for healthcare professionals. Interventions should consider shift scheduling, adequate recovery time, sufficient sleep duration, appropriate nutrition, physical activity, and periodic metabolic screening.

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