Factors associated with the occurrence of functional dyspepsia and insomnia in shift-working nurses

Abstract

BACKGROUND: In South Korea, people are growing more and more interested in the early detection and prevention of health problems in shift workers.

OBJECTIVE: This study aims to investigate demographic, work-related and health-related factors relevant to functional dyspepsia and insomnia in shift-working nurses in South Korea.

METHODS: The sample was comprised of 1431 nurses who worked rotating shifts in three large hospitals in Seoul and Gyeonggi Province, South Korea. The questionnaire consisted of factors assessing demographic, work-related and health-related characteristics. Rome III criteria and the Insomnia Severity Index were applied to identify functional dyspepsia and insomnia, respectively. The survey was ongoing for approximately one month starting from 17 June 2013.

RESULTS: The results of this study indicated that gender, body mass index, the number of night shifts worked, work-related stress, and regular dietary patterns were related to functional dyspepsia and insomnia in shift-working nurses.

CONCLUSIONS: This study may help establish suitable working conditions and build workplace health promotion programs for shift-working nurses.

Keywords

Shift work occupational health sleep disorders digestive system diseases

1 Introduction

Shift work refers to all types of work done after normal daytime working hours (from 6 a.m. to 7 p.m.) [1]. Evening shifts, night shifts, early morning shifts, and rotating shifts all fall into this category. Since the advent of modern civilization, there has been a growing need for jobs to be performed after daytime working hours, which has increased the number of shift workers. According to the results of a survey conducted by the European Foundation in 2010, more than 17% of workers in the European Union (EU) engaged in shift work, including night work [2]. In South Korea, according to 2010 statistics, 11% of the employed population worked at night [3].

According to previous research, shift work is not in line with normal circadian rhythms, and it therefore interferes with the normal sleep/wake cycle [4]. It also increases stress by reducing opportunities to take part in social and family activities [4]. As a result, shift work leads to health problems by causing behavioral changes, such as smoking, drinking and irregular meal patterns [4]. Reported health problems mainly include sleep disorders like insomnia [5], digestive disorders, including loss of appetite and indigestion [6], damage caused by sleepiness and fatigue at work [7], cardiovascular diseases like stroke and myocardial infarction [8], and breast cancer [9].

Not every shift worker, however, complains of these health problems because workers have different levels of shift-work tolerance [1]. In 1979, Andlauer and colleagues introduced the concept of shift-work tolerance, which refers to a person’s ability to adapt to shift work without adverse consequences, such as sleep disorders, digestive disorders, fatigue, and depressed mood [10]. Shift-work tolerance varies according to gender, age, number of children, morningness/eveningness, stress, drinking habits, and the number of night shifts and weekly working hours [1, 11, 12].

The International Agency for Research on Cancer (IARC) classified shift work that included night shifts as a probable human carcinogen in 2007 [13], and since then, the interest in shift workers’ health has been growing exponentially in South Korea. Also, after labor unions of several medical institutions reported a high rate of spontaneous abortion and cancer among shift-working nurses [14], much of the population is now showing an interest in shift workers’ health. In response, the South Korean Ministry of Employment and Labor has developed a policy to make it mandatory for night-shift workers to receive regular occupational medical examinations beginning in 2014 in an effort to detect and treat their health problems early [15].

While check-ups are important in early detection of health problems caused by shift work, it is also a good strategy to establish proper working conditions and promote workers’ suitability for shift work. To that end, information regarding the factors that affect shift workers’ health needs to be collected. While most of the domestic research done so far has examined the relationship between shift work and stress, sleep, cardiovascular diseases, or work-related injuries [16], investigations and research on factors that influence shift workers’ health problems are insufficient. Even though various factors affecting shift-work tolerance have been studied since the 1990s [1, 11], it is inappropriate to apply the outcomes directly to South Korean workers as most of the studies targeted Caucasians in Western countries. South Korean workers have different working conditions and different demographic characteristics from workers in Western countries. For example, in general, South Korean workers work longer than Western workers (2012 average annual working hours per worker; South Korea 2163 vs. U.S. 1799) [17] and are younger than Western workers (2010 workers’ median age; South Korea 39.9 vs. U.S. 41.9) [18, 19]. Therefore, in order to identify the factors associated with South Korean shift workers’ health problems, this study compared the characteristics of shift workers according to whether they had experienced functional dyspepsia or insomnia, which are among the common health problems reported by shift workers [20]. The specific goals were as follows:

First, compare shift workers’ characteristics according to the occurrence of functional dyspepsia and insomnia.

Second, identify the factors that are associated with the occurrence of functional dyspepsia and insomnia in shift workers.

The outcomes of this study can be utilized as basic information in improving shift workers’ health and establishing a healthy work environment for shift workers. This study is especially critical at the moment as the South Korean government is beginning to make proactive efforts to protect shift workers’ health.

2 Methods

2.1 Study design

This study is a descriptive correlational study intended to identify factors that might be associated with functional dyspepsia and insomnia in shift workers. The study collected data by conducting a cross-sectional survey.

2.2 Sampling and data collection

The participants were nurses who worked rotating shifts in three general hospitals in Seoul and Gyoenggi Province. First, the study was approved by Institutional Review Board (IRB) of The Catholic University of Korea as well as by the directors of nursing of the three general hospitals. Interviewers visited every inpatient ward, outpatient department, and special department – operating rooms, intensive care units and delivery rooms – of the three hospitals to directly recruit participants, obtain informed consent, and carry out the survey. The survey took place for approximately a month beginning on 17 June 2013. In total, 1487 nurses participated in the survey. After incomplete questionnaires were excluded, the final analysis included replies from 1431 participants.

2.3 Instruments

The structured questionnaire developed for the study consisted of five categories: demographic characteristics, work-related characteristics, health-related characteristics, functional dyspepsia, and insomnia.

2.3.1 Demographic characteristics

Demographic characteristics included gender, age, marital status, and the number of children living with the participant.

2.3.2 Work-related characteristics

The participants’ department, position, weekly working hours, average number of night shifts worked per month, night shift experience, and work-related stress were all types of work-related characteristics. Work-related stress was measured using the Korean Occupational Stress Scale (KOSS) [21]. The KOSS consists of eight subcategories: job demand, job control, interpersonal conflicts, job insecurity, organizational system, lack of rewards, workplace culture, and physical environments. This inventory contains a total of 27 questions with a4-point scale. The higher the score, the higher the stress level. The reliability of the KOSS was validated in previous research [22], and its Cronbach’s alpha was 0.78 in this study.

2.3.3 Health-related characteristics

Health-related characteristics included height, weight, smoking status, frequency and amount of alcohol use, number of days the participant took part in physical activities, and meal regularity. Height and weight, collected through self-reports, were converted into body mass index (BMI). Based on the criteria for Asian adults developed by the World Health Organization (WHO), people with a BMI <18.5 were categorized as underweight; those from 18.5–23 were normal, 23–25 as overweight, and >25 as obese [23]. Excessive drinkers were distinguished by the frequency and amount of alcohol they used. Women who drank twice or more a week and consumed five glasses or more at a time, and men who drank twice or more a week, drinking seven glasses or more per use, were defined as excessive drinkers [24]. The study also researched the number of days participants engaged in moderate-intensity physical activities (swimming, doubles tennis, volleyball, badminton, table tennis, moving light-weight items, etc.) for more than 30 minutes. The regularity of meal patterns was surveyed using a single 5-point-scale question (1: very irregular-5: veryregular).

2.3.4 Functional dyspepsia

In order to assess shift workers’ functional dyspepsia, the Rome III criteria, suggested by the Rome Foundation, were applied [25]. For a diagnosis of functional dyspepsia, one or more of the symptoms of postprandial fullness, early satiety and epigastric burning should be present and last for three months, with the first symptom starting at least six months prior to the diagnosis [25]. Previous studies have validated the Rome III criteria to have reasonable test-retest reliability [26].

2.3.5 Insomnia

The Insomnia Severity Index (ISI) was used to measure the symptoms and consequences of insomnia [27]. The ISI consists of seven questions with a 5-point scale (0: not at all-4: very serious); participants who score eight points or higher are classified as having insomnia. The tool’s validity and reliability were proven in previous studies [28]. In this study, the ISI Cronbach’s alpha was 0.87.

2.4 Data analysis

The collected data were analyzed using the Statistical Package for the Social Sciences (SPSS), version 21 (IBM Corp., Armonk, NY, US). The demographic, work-related and health-related characteristics of the participants were evaluated using descriptive statistics. The t-test and χ²-test were conducted to compare shift workers’ characteristics according to the occurrence of functional dyspepsia and insomnia. Logistic regression analysis was used to determine the odds ratio (OR) of the main explanatory variables for such symptoms. Dependent variables were the occurrence of functional dyspepsia and insomnia, while independent variables included 14 factors: gender, age, marital status, the number of children, department, position, length of night-shift experience, working hours, the number of night shifts, work-related stress, BMI, excessive drinking, physical activities, and regularity of meal patterns.

3 Results

3.1 Characteristics of participants

The characteristics of the participants are represented in (Table 1). The average age was 28; 98% of the participants were female, and 80% were single. The married respondents had one child on average.

Of the total participants, 58% worked in inpatient wards and 97% were staff nurses. Their average length of night shift experience was four years. On average, they worked 47 hours a week and five nights a month. The mean KOSS score (work-related stress level) of the participants was 50 points. Of the total participants, 70% had a normal BMI, 1% were smokers and 7% were excessive drinkers. The participants engaged in moderate-intensity physical activities once a week on average. The score of their meal regularity was two points on average, which means they are eating at irregular times.

3.2 Comparison of shift workers’ characteristics according to functional dyspepsia

The differences in shift workers’ characteristics according to the occurrence of functional dyspepsia are shown in (Table 2). The proportion of females (99% vs. 98% p < 0.05 : 95% confidence interval, 0.20% to 2.84%) and single people (83% vs. 78%, p < 0.05) was higher among workers with functional dyspepsia than among those who did not suffer from dyspepsia.

The participants with functional dyspepsia included a higher proportion of nurses working in inpatient wards than those without functional dyspepsia (67% vs. 53%, p < 0.001). In addition, the shift workers with the disease had longer weekly working hours (49 hours/week vs. 47 hours/week, p < 0.001), more days of night shift work per month (5.3 days/month vs. 5.0 days/month, p < 0.05) and higher scores for work-related stress (53 points vs. 50 points, p < 0.001).

The shift workers with functional dyspepsia also showed a higher proportion of underweight people (23% vs. 18%, p < 0.05), a lower rate of obesity (2% vs. 5%, p < 0.05), a higher proportion of excessive drinking (9% vs. 6%, p < 0.05), and a lower score for meal regularity (1.9 points vs. 2.2 points, p < 0.001) compared to those without the condition.

3.3 Comparison of shift workers’ characteristics according to insomnia

The differences in shift workers’ characteristics according to the occurrence of insomnia are shown in (Table 2). In the participants who had insomnia, the proportion of singles was higher than it was in those who did not suffer from insomnia (82% vs. 74%, p < 0.01).

A large percentage of nurses working in inpatient wards reported insomnia (60% vs. 51%, p < 0.01). At the same time, respondents with insomnia also included a higher proportion of staff nurses (98% vs. 94%, p < 0.01), and they had more days of night shift work per month (5.2 days/month vs. 4.7 days/month, p < 0.001) and a higher score in work-related stress (51 points vs. 49 points, p < 0.001) than those without insomnia.

The participants with insomnia spent fewer days engaging in moderate-intensity physical activities (1.5 days/week vs. 1.8 days/week, p < 0.05) and ate meals more irregularly than those without the condition (2.0 points vs. 2.5 points, p < 0.001).

3.4 Factors associated with functional dyspepsia in shift workers

The results of a logistic regression to identify the associated factors of functional dyspepsia in shift workers are shown in (Table 3). According to the analysis, those working in special departments were less likely to experience functional dyspepsia than those who worked in inpatient wards (odds ratio [OR] = 0.62, 95% confidence interval [CI]: 0.49–0.78). The OR for the work-related stress coefficient was 1.37 with a 95% CI of [1.09, 1.73]. This suggested that shift workers who recorded higher-than average scores (average: 50.2 points) in work-related stress were almost 1.5 times more likely to experience functional dyspepsia than those with lower-than average scores. Obese people had lower odds of functional dyspepsia than those who were underweight (OR = 0.32, 95% CI: 0.15–0.67), and shift workers who drank excessively were more likely to experience functional dyspepsia (OR = 1.59, 95% CI: 1.02–2.46). Workers with higher-than-average (average: 2.01 points) scores for meal regularity (OR = 0.67, 95% CI: 0.50–0.91) had a lower chance of experiencing functional dyspepsia. The goodness of fit of this logistic regression model was found to be statistically meaningful (χ² = 424.31,p < 0.001).

3.5 Factors associated with insomnia in shift workers

As a result of the logistic regression to identify the factors influencing insomnia in shift workers, the associated factors were gender, the number of night shifts worked per month, work-related stress, and meal regularity (Table 3). According to the study’s results, female shift workers were more likely to experience insomnia than their male counterparts (OR = 5.88, 95% CI: 3.70–9.34), and shift workers who worked more than an average of 4.9 days of night shift work per month showed a higher tendency to experience insomnia than those working less than 4.9 days/month (OR = 1.39, 95% CI: 1.05–1.83). Shift workers recording average (50.2 points) or higher scores in work-related stress were more likely to suffer from insomnia than those with lower-than-average scores (OR = 1.51, 95% CI: 1.16–1.98). Also, the odds of developing insomnia were lower in shift workers with higher-than-average (average: 2.1 points) scores in meal regularity (OR = 0.71, 95% CI: 0.53–0.96). The goodness of fit of this logistic regression model was statistically meaningful (χ² = 546.36, p < 0.001).

4 Discussion

4.1 Demographic characteristics and functional dyspepsia and insomnia

This study’s findings revealed that there were statistically significant differences in the occurrence of functional dyspepsia according to gender and marital status. These findings are supported by other research. A study conducted by Chithra et al. [29] reported functional dyspepsia was more prevalent in females than in males, while another study concluded that single people were more likely to have functional dyspepsia than those who were married [30]. However, the reasons for these associations are unknown.

In this current study, gender was found to be a significant variable for predicting insomnia in shift workers. This result is in consistent with that of Admi and colleagues who found that female shift workers complained more about sleep disorders than male shift workers [31]. The reasons for such gender differences could be explained by hormonal fluctuations during the menstrual or estrous cycle, a factor that can be associated with sleep disturbances [32].

4.2 Work-related characteristics and functional dyspepsia and insomnia

According to our research, nurses working in inpatient wards were more likely to experience functional dyspepsia. This is likely due to their greater exposure to work-related and client-related stress since they have a higher chance of being involved in difficult psychosocial situations of their clients and have less autonomy in their work compared to nurses who work in special departments [33].

This study found that nurses working 5 or more nights a month were more likely to experience insomnia. Another study also identified the number of night shifts worked as a significant factor of increased insomnia [34].

As seen from the results of the current study, a high level of work-related stress increased the incidence of insomnia [12]. Work-related stress was also an important factor for digestive disorders [6, 35]. Previous studies have also demonstrated that working long hours has negative effects on shift workers’ health [11, 36].

4.3 Health-related characteristics and functional dyspepsia and insomnia

This research found that obese shift workers were less likely to experience functional dyspepsia than their underweight counterparts. This result is in contrast with that of most of the existing studies. Many other studies have reported the average BMI of patients with digestive disorders was higher than that of people without these diseases [37]. However, a study on South Korean adults using the Rome III criteria, which was the same tool used in this current study, found that people with BMIs that were 25 or higher showed the lowest frequency of functional dyspepsia [38]. As South Koreans have grown more interested in obesity and weight-control, it is common for them to control their diets to shed weight [39]. In particular, the symptoms of functional dyspepsia exacerbated after people tried to control their weight through fasting or skipping meals [40]. Excessive ways to lose weight such as fasting and skipping meals can increase the likelihood of developing functional dyspepsia [40].

This study observed there were many excessive drinkers among the shift workers who complained about functional dyspepsia. Shift workers often consume alcohol as a method to aid in sleeping [41]. However, since alcohol has been reported to disturb sleep instead of promoting it [42], it is better for shift workers to find a healthy sleep-improving method (e.g., keeping bedroom dark, establishing a bedtime routine, or avoiding caffeine) instead of relying on alcohol [43].

Shift workers tend to follow irregular meal patterns due to their working conditions [44], which can exacerbate digestive disorders [6, 45]. Additionally, diets imbalanced in fat, protein and carbohydrates can cause sleep disorders like insomnia [46]. In the current study as well, irregular meal schedules had an effect on functional dyspepsia and insomnia. Therefore, to treat shift workers’ digestive and sleep problems, workers should make efforts to eat healthily and workplaces should also provide nutrition interventions to improve workers’ diet since they spend most of their time at work.

According to this study, shift workers suffering from insomnia engaged in physical activities less frequently than workers who slept well. In general, shift workers have fewer opportunities to work out. However, good exercise habits are recommended for shift workers, since physical activities can help treat sleep problems [42]. About 20 minutes of aerobic exercise before going to work can help workers to wake up and also will improve their cardiopulmonary function [47]. Shift workers should avoid working out up to three hours before going to bed, since this activity can make it difficult for them to enter a deep, sound sleep [47].

5 Implications

This study found functional dyspepsia and insomnia among shift workers are associated with the number of night shifts, stress level, drinking habits, weight, and meal regularity. Even though this cross-sectional study has a limitation in demonstrating a clear causality, considering the results of this study and other existing ones, following suggestions can be a help in reducing functional dyspepsia and insomnia in shift workers: minimizing the number of night shifts, introducing stress-management programs or mental counseling services to help workers reduce stress, refraining from excessive use of alcohol, developing healthy eating habits.

6 Conclusions

This study found that shift workers with functional dyspepsia were more likely to be female, be underweight, work in inpatient wards, work longer hours, spend more nights at work, experience high levels of work-related stress, drink excessively, and have irregular meals. Shift workers with insomnia were more likely to be single, work in inpatient wards, be staff nurses, spend more nights at work, experience high levels of work-related stress, engage in fewer physical activities, and have irregular meals. The factors associated with functional dyspepsia and insomnia in shift workers were gender, department, drinking habits, BMI, the number of night shifts worked each month, work-related stress, and mealregularity.

The limitations of the study are as follows. First, workers who fail to adapt to shift work and develop health problems may quit or transfer to day shifts. These workers who drop out of shift work could act as an obstacle to an accurate understanding of the characteristics of shift workers with health problems as they were not surveyed. Second, since this study was based on a cross-sectional design, it is insufficient to determine a causal relationship; a well-designed longitudinal study will be needed to clearly identify the relevant factors of shift workers’ health problems. Third, as the study relied on convenience sampling, its results should be applied with caution to the entire nursing population in South Korea. In fact, the participants of this research study were younger than those who took part in the South Korean Nurses’ Survey, a large-scale study conducted in 2011 [48]. Since young workers tend to underreport their work-related injuries [49], the current study might not have identified all the workers with functional dyspepsia and insomnia accurately. Lastly, meal regularity was distinguished using a single-item measure that has not had its reliability and accuracy validated. To determine the validity and accuracy of this single-item measure for assessing meal regularity, tests on its psychometric properties should beperformed.

Conflict of interest

None to disclose.

Footnotes

Acknowledgments

This study was supported by the 2014 Research Fund from the University of Ulsan in South Korea (2014-0089).

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