Volume 3, Issue 2 (May 2018)                   JNFS 2018, 3(2): 94-100 | Back to browse issues page

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Rezaei Hachesu V, Naderyan Feli S. Association between Shift Working and Markers of Obesity: A Cross Sectional Study on Taxi Drivers in Yazd, Iran. JNFS. 2018; 3 (2) :94-100
URL: http://jnfs.ssu.ac.ir/article-1-162-en.html
Department of Biostatistics and Epidemiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
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Association between Shift Working and Markers of Obesity: A Cross Sectional Study on Taxi Drivers in Yazd, Iran
 
Vida Rezaei Hachesu; MSc1 & Shadi Naderyan Feli; MSc*2
 
1 Department of Occupational Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
2Department of Biostatistics and Epidemiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
 
ARTICLE INFO   ABSTRACT
ORIGINAL ARTICLE Background: Obesity is one of the most important health problems, so it is very important to identify its causes. Shift work is one of the factors that causes people to become obese. The aim of this study was to examine the relationship between shift work and obesity in taxi drivers. Methods: In this cross sectional study conducted in 2016, 120 male taxi drivers from Yazd were studied for demographic characteristics and some anthropometric indices. To describe the data, descriptive statistics were used; to compare the prevalence of overweight, general and abdominal obesity, chi-square test was used and to compare quantitative variables, independent t-test and Mann-Whitney test were used. Results: The results showed that the mean weight, waist circumference, body mass index and waist to hip ratio (WHR) were significantly higher in shift workers (P < 0.05). In this study, the prevalence of overweight in shift and day workers was 41.4 and 46% (P = 0.61), general obesity was 34.3 and 20% (P = 0.08), and abdominal obesity was 82.9 and 82% (P = 0.90), respectively. Spearman correlation coefficient showed a positive and significant correlation between age and WHR as well as work experience and WHR in shift workers (r = 0.34 and r = 0.31, respectively). Also, a positive and significant correlation was found between age and WHR in day workers (r = 0.35). Conclusions: The results of this study showed that shift work in taxi drivers is associated with an increased probability of overweight, general and abdominal obesity.
Keywords: Taxi drivers; Shift work; Obesity
Article history:
Received: 29 Jul 2017
Revised: 7 Sep 2017
Accepted: 4 Nov 2017
*Corresponding author:
Naderyan67@yahoo.com
Department of Biostatistics and Epidemiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
 
Postal code: 8915173160
Tel: +983538209114
 
Introduction
Any work done out of the usual daily working hours (contracted from 7 a.m. to 6 p.m.) is considered shift work. Shift work is one of the stressful occupational factors and has adverse effects on the human health (Wang et al., 2011). Shift work in terms of various aspects can have devastating effects on the physical and mental health, safety, efficiency, family and social status (Bøggild and Knutsson, 1999, Knutsson, 2003). Shift work-related diseases mentioned in some studies can be cardiovascular diseases, digestive disorders, diabetes, cancer, and metabolic disorders (Kim et al., 2013, Tada et al., 2014). The mechanisms that link shift work to health problems are not entirely clear, but changes in circadian rhythm, sleep problems, stress, inappropriate lifestyle like unbalanced diets and smoking are potential causes (Knutsson, 2003). Weight gain in shift workers can be attributed to several factors such as genetic factors, glucose and lipid hemostasis, thrombogenic responses, nutritional patterns at night, and hormonal neurological factors such as leptin and ghrelin (Antunes et al., 2010).
Obesity is a risk factor for many chronic diseases. Many studies have demonstrated that the prevalence of overweight and obesity among shift workers is higher than that of day workers (Di Lorenzo et al., 2003, Macagnan et al., 2012). Some studies also have pointed to the relationship between obesity and shift work (Manenschijn et al., 2011, Samara et al., 2016, Van Drongelen et al., 2011). In the study conducted by Kim et al. among female nurses, the prevalence of overweight and obesity was significantly higher in shift work nurses (18.6 and 7.4%, respectively) (Kim et al., 2013). In addition, the results of the 14-year retrospective cohort study of 7,254 male workers from Japan steel industries between 1991 and 2005 by Suwazon et al. showed that rotational shift work is an independent risk factor for obesity (Suwazono et al., 2008).
Today, obesity is a major health concern and drivers, especially those who have shift working, are among the most at risk groups. Despite that, association between shift work and obesity has not been well known (Kim et al., 2013, Peplonska et al., 2015, Tada et al., 2014) and the status of obesity in shift work taxi drivers has been less frequently studied. Therefore, the present study was conducted to examine the relationship between shift work and obesity of urban taxi drivers in Yazd city in Iran.
Materials and Methods
Study design: The present study is a cross sectional study that was conducted in the spring of 2016 among 120 taxi drivers of Yazd in two groups of shift workers (n = 70) and day workers (n = 50). Sampling was done by a simple random sampling method and using a sampling frame; so that the list of drivers' names was taken from the taxi :union: and then numbered, after that, the names were removed and 120 numbers (drivers) were selected randomly from the numbers. The number of samples required for the study was calculated by taking into consideration p = 0.22 of similar studies and d = 0.07 using the sample size formula for estimating the proportion. The inclusion criterion was working at least one year in Yazd taxi and having a second job was the exclusion criterion. In this study, shift work was defined as working hours out of 7 a.m. to 6 p.m. when drivers work rotationally in day-to-day taxi.
Data collection: Age, work experience and work system (shift work/day work) were recorded based on verbal interview of the subjects. The weight was measured by a calibrated digital scale (Omron, Japan) and the height was measured by placing the heel, hip and head in a direction by the fixed tape meter on the wall. The waist circumference was measured in the interspaced area between the last rib and the iliac crest (WHO, 2011) and the hip circumference was measured in the area of the largest pelvic circumference area using a non-elastic strip meter. The above measurements were performed with minimum coverage and no shoes.
 Body mass index (BMI) was calculated based on the weight in kilograms divided by height squared in meters. According to WHO recommendation for Asian populations, the range of this index from 18.5-24.9 kg/m² was normal weight, 25-29.9 kg/m² was overweight and equal or greater than 30 kg/m² was general obesity (WHO, 2004). By dividing the waist circumference by the hip circumference the waist to hip ratio (WHR) was obtained. According to WHO criteria, if this value is greater than or equal to 0.90 in men, it is considered as abdominal obesity (WHO, 2011).
Data analysis: The data were analyzed using SPSS 16 software. The descriptive statistics
(mean, standard deviation, and frequency distribution table) were used to describe the data.
To compare the grouping variables, chi-square test was used and for the comparison of quantitative variables, independent t-test and Mann-Whitney U test were used. The significance level of statistical tests was considered as P < 0.05.
Ethical considerations: This study was conducted after obtaining the approval of the Ethics Committee of Shahid Sadoughi University of Medical Sciences in Yazd, and the informed consent of all participants in the research was taken.
Results
All subjects were male in this study. A total of 41.7% of them were day drivers and 58.3% of them were shift drivers. In Table 1, the mean and standard deviation of the demographic and anthropometric variables of the subjects are presented in terms of the shift work status. According to this table, the mean weight, waist circumference, BMI and WHR in shift drivers was significantly higher than that of day drivers (P < 0.05). No significant difference was found between the mean age, work experience, height and hip circumference in the two groups.
The prevalence of general and abdominal obesity in shift drivers was higher than that of day drivers, but the prevalence of overweight is higher in day drivers (Table 2).
The prevalence of overweight in those who worked 8 hours and less per day was higher than those who worked more than 8 hours. The prevalence of general and abdominal obesity among those who worked more than 8 hours per day was higher than those who worked 8 hours and less (Table 3).
Based on the correlation coefficients presented in Table 4, a positive and highly-significant correlation was found between age and WHR as well as work experience and WHR among shift drivers (P = 0.004 and P = 0.008, respectively). Also, a positive and significant correlation was seen between age and WHR among day drivers (P = 0.011).
Table 1. The demographic and anthropometric variables of the participants
 
Variables Mean SD P-value
Age (year)
    Shift work
    Day work
 
48.60 12.67
44.08 10.54
 
0.08a
 
Work experience (year)
    Shift work
    Day work
 
11.24 7.11
11.40 9.32
 
0.55
 
Weight (kg)
    Shift work
    Day work
 
84.52 14.35
78.27 10.62
 
0.01a
Height (cm)
    Shift work
    Day work
 
172.65 6.47
171.58 7.02
 
0.39b
 
Waist circumference (cm)
    Shift work
    Day work
 
100.43 15.70
96.86  7.59
 
0.04a
Hip circumference (cm)
    Shift work
    Day work
 
105.31 12.35
103.48  5.49
 
0.12a
 
Body mass index (kg/m2)
    Shift work
    Day work
 
28.33 4.31
26.59 3.27
 
0.01 b
 
Waist to hip ratio
    Shift work
    Day work
 
0.96 0.16
0.94 0.04
 
0.04a
a: Mann-Whitney U test; b:Student t-test    
 
Table 2. Comparison of shift and day drivers' anthropometric status
 
Variables N (%) P-valuea
Normal body mass index
    Shift work
    Day work
 
14 (20.0)
16 (32.0)
 
0.13
 
Overweight
    Shift work
    Day work
 
29 (41.4)
23 (46.0)
 
0.61
 
General obesity
    Shift work
    Day work
 
24 (34.3)
10 (20.0)
 
0.08
Abdominal obesity
    Shift work
    Day work
 
58 (82.9)
41 (82.0)
 
0.90
a: Chi-square test
 
Table 3. Comparison of the participants' anthropometric status according to working hours
 
Variables Working hours N (%) P-valuea
Normal body mass index 8 hours and less 16 (32.0) 0.13
more than 8 hours 14 (20.0)
Overweight 8 hours and less 23 (46.0) 0.61
more than 8 hours 29 (41.4)
General obesity 8 hours and less 10 (20.0) 0.08
more than 8 hours 24 (34.3)
Abdominal obesity 8 hours and less 41 (82.0) 0.90
more than 8 hours 58 (82.9)
a: Chi-square test
 
Table 4. Correlation coefficient between studied variables
 
Variables Spearman correlation coefficient P-value
Age & Body mass index
    Shift work
    Day work
 
0.009
0.121
 
0.941
0.402
Work experience & Body mass index
    Shift work
    Day work
 
0.141
0.008
 
0.246
0.956
Age & Waist to hip ratio
    Shift work
    Day work
 
0.344
0.357
 
0.004
0.011
Work experience & Waist to hip ratio
    Shift work
    Day work
 
0.313
0.130
 
0.008
0.367

 
Discussion
In our study, the mean weight, waist circumference, BMI and WHR were significantly higher among shift workers. In Uki Tada study on female nurses, the mean BMI was significantly higher in shift workers than in day workers (Tada et al., 2014). In Ishizaki study on workers of a metal melting plant, the mean BMI and WHR were significantly higher in shift workers than in day workers (Choi et al., 2017). Moreover, in the study conducted by Marqueze et al. on truck drivers, the mean BMI was significantly higher in shift workers than in day workers (Marqueze et al., 2013), which is in line with our study results. The results of our study indicated the high prevalence of overweight and general obesity, as well as very high prevalence of abdominal obesity among all the studied drivers (shift and day workers). In addition, general and abdominal obesity was more frequent among shift workers than day workers. These results are consistent with the results of several studies (Chen et al., 2010, Kim et al., 2013, Peplonska et al., 2015). The mechanism of the relationship between shift work and weight gain has not been fully explained. Despite this, several factors such as unhealthy food habits, sleep deprivation, circadian rhythm disorder and low level of physical activity have been suggested as potential causes (Lowden et al., 2010). Sleep deprivation and circadian rhythm disorder affect the mechanisms of metabolism and hunger, leading to unhealthy nutritional behaviors, which include irregular meals, high caloric and low fiber food consumption, along with frequent sweets during the night. On the other hand, studies have shown that lack of sleep leads to a reduction in the concentration of leptin and an increase in the concentration of ghrelin, which likely leads to an increase in appetite and overweight (Chen et al., 2010, Lemke et al., 2015). Furthermore,
shift working may lead to stress. Chronic activation of stress system including secretion of glucocorticoids and catecholamine from the adrenal gland may result in abdominal adiposity and other metabolic disorders (Wang et al., 2011).
Several studies have reported that workers with more working hours have higher BMI (Bray and Young, 2007, Magee et al., 2011), confirming our study results; where the prevalence of general and abdominal obesity in those who worked more than 8 hours per day was higher, compared with drivers who worked 8 hours and less. Long working hours can lead to sleep and circadian rhythms disorders, both of which play an important role in metabolic problems such as obesity (Scott et al., 2008). Studies have shown that those who have long working hours are less likely to exercise, eat faster and spend more time watching television, which can lead to weight gain (Basner et al., 2007, Lemke et al., 2015). Driving is one of the most stressful occupations (Scott et al., 2008). Moreover, since stress can lead to some undesired behaviors, it plays an important role in the relationship between working hours and obesity. On the other hand, those who have long working hours are more likely to be exposed to stress and exhibit undesired behaviors such as smoking, alcohol consumption as well as overeating as a way to manage their stress (Ishizaki et al., 2004). Stress also causes cortisol secretion, which leads to weight gain (Gu et al., 2012).
In this study, a positive and significant correlation was seen between age and WHR and between work experience and WHR. Also, this can be justified given the fact that those with higher work experience will have a cumulative effect of disorders in the body's circadian rhythm, inappropriate nutrition, inactivity, and other factors. Also, aging can justify a positive correlation with abdominal obesity by this mechanism.
Given that the present study is a cross-sectional study, it is impossible to establish a causal relationship between shift work and overweight or obesity. Other limitations of this study include lack of control group, non-participation of female drivers and the lack of control of some confounding variables, for example, it has not been determined whether the subjects were overweight and obese after entering the job, or were also obese before entering. Furthermore, individuals with certain obesity related diseases, such as depression, Hypothyroidism, were not excluded. Studies on examining the relationship between shift work and obesity of taxi drivers in our country are a handful. For this reason, conducting the present study is one of its strengths; in addition, it is suggested to conduct more comprehensive studies with a larger sample size and considering female drivers as well as the control group.
Conclusion
According to the results of this study, shift work can be considered as an effective factor on overweight and obesity. Regular measurement of anthropometric indices such as body mass index, modification of individual habits such as following a balanced nutrition program and having sufficient physical activity among drivers, especially shift work drivers, is strongly recommended.
Acknowledgment
The authors are grateful to the honorable staff of Yazd taxi :union: that helped in carrying out this research.
Author's contribution
The study was designed by Rezaei Hachesu  V and statistical analysis was performed by Naderyan Feli S. Data collection and writing manuscript were performed by both authors. Both authors reviewed the paper and confirmed it.
Conflict of interest
The authors have no conflicts of interest to report.
 
References
Antunes L, Levandovski R, Dantas G, Caumo W & Hidalgo M 2010. Obesity and shift work: chronobiological aspects. Nutrition research reviews. 23 (1): 155-168.
Basner M, et al. 2007. American time use survey: sleep time and its relationship to waking activities. Sleep. 30 (9): 1085-1095.
Bøggild H & Knutsson A 1999. Shift work, risk factors and cardiovascular disease. Scandinavian journal of work, environment & health. 25 (2): 85-99.
Bray M & Young M 2007. Circadian rhythms in the development of obesity: potential role for the circadian clock within the adipocyte. Obesity reviews. 8 (2): 169-181.
Chen C-C, et al. 2010. Shift Work and Arteriosclerosis Risk in Professional Bus Drivers. Annals of epidemiology. 20 (1): 60-66.
Choi B, et al. 2017. A socioecological framework for research on work and obesity in diverse urban transit operators based on gender, race, and ethnicity. Annals of occupational and environmental medicine. 29 (1): 15.
Di Lorenzo L, et al. 2003. 1283801. Effect of shift work on body mass index: results of a study performed in 319 glucose-tolerant men working in a Southern Italian industry. International journal of obesity. 27 (11): 1353-1358.
Gu MJK, et al. 2012. Long work hours and adiposity among police officers in a US northeast city. Journal of occupational and environmental medicine. 54 (11): 1374.
Ishizaki M, et al. 2004. The influence of work characteristics on body mass index and waist to hip ratio in Japanese employees. Industrial health. 42 (1): 41-49.
Kim M-J, et al. 2013. Association between shift work and obesity among female nurses: Korean Nurses’ Survey. BMC public health. 13 (1): 1204.
Knutsson A 2003. Health disorders of shift workers. Occupational medicine. 53 (2): 103-108.
Lemke MK, Hege A, Perko M, Sönmez S & Apostolopoulos Y 2015. Work patterns, sleeping hours and excess weight in commercial drivers. Occupational medicine. 65 (9): 725-731.
Lowden A, Moreno C, Holmbäck U, Lennernäs M & Tucker P 2010. Eating and shift work—effects on habits, metabolism, and performance. Scandinavian journal of work, environment & health. 36 (2): 150-162.
Macagnan J, et al. 2012. Impact of nightshift work on overweight and abdominal obesity among workers of a poultry processing plant in southern Brazil. Chronobiology international. 29 (3): 336-343.
Magee CA, Caputi P & Iverson DC 2011. Short sleep mediates the association between
long work hours and increased body mass index. Journal of behavioral medicine. 34 (2): 83-91.

Manenschijn L, van Kruysbergen RG, de Jong FH, Koper JW & van Rossum EF 2011. Shift work at young age is associated with elevated long-term cortisol levels and body mass index. Journal of clinical endocrinology & metabolism. 96 (11): E1862-E1865.
Marqueze EC, Ulhôa MA & Moreno CRdC 2013. Effects of irregular-shift work and physical activity on cardiovascular risk factors in truck drivers. Revista de saude publica. 47 (3): 497-505.
Peplonska B, Bukowska A & Sobala W 2015. Association of rotating night shift work with BMI and abdominal obesity among nurses and midwives. PLoS One. 10 (7): e0133761.
Samara D, Merijanti LT, Tandean R & Harrianto R 2016. The association between shift work and body mass index among female nurses. Universa medicina. 27 (2): 72-77.
Scott E, Carter A & Grant P 2008. Association between polymorphisms in the Clock gene, obesity and the metabolic syndrome in man. International journal of obesity. 32 (4): 658.
Suwazono Y, et al. 2008. A longitudinal study on the effect of shift work on weight gain in male Japanese workers. Obesity. 16 (8): 1887-1893.
Tada Y, et al. 2014. Association of body mass index with lifestyle and rotating shift work in Japanese female nurses. Obesity. 22 (12): 2489-2493.
Van Drongelen A, Boot CR, Merkus SL, Smid T & Van Der Beek AJ 2011. The effects of shift work on body weight change—a systematic review of longitudinal studies. Scandinavian journal of work, environment & health. 37 (4): 263-275.
Wang X, Armstrong M, Cairns B, Key T & Travis R 2011. Shift work and chronic disease: the epidemiological evidence. Occupational medicine. 61 (2): 78-89.
World Health Organization 2004. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 363 (9403): 157-163.
World Health Organization 2011. Waist circumference and waist-hip ratio: Report of a WHO expert consultation, Geneva, 8-11 December 2008.

 
Type of article: orginal article | Subject: public specific
Received: 2018/05/1 | Accepted: 2018/05/1 | Published: 2018/05/1

References
1. Antunes L, Levandovski R, Dantas G, Caumo W & Hidalgo M 2010. Obesity and shift work: chronobiological aspects. Nutrition research reviews. 23 (1): 155-168.
2. Basner M, et al. 2007. American time use survey: sleep time and its relationship to waking activities. Sleep. 30 (9): 1085-1095.
3. Bøggild H & Knutsson A 1999. Shift work, risk factors and cardiovascular disease. Scandinavian journal of work, environment & health. 25 (2): 85-99.
4. Bray M & Young M 2007. Circadian rhythms in the development of obesity: potential role for the circadian clock within the adipocyte. Obesity reviews. 8 (2): 169-181.
5. Chen C-C, et al. 2010. Shift Work and Arteriosclerosis Risk in Professional Bus Drivers. Annals of epidemiology. 20 (1): 60-66.
6. Choi B, et al. 2017. A socioecological framework for research on work and obesity in diverse urban transit operators based on gender, race, and ethnicity. Annals of occupational and environmental medicine. 29 (1): 15.
7. Di Lorenzo L, et al. 2003. 1283801. Effect of shift work on body mass index: results of a study performed in 319 glucose-tolerant men working in a Southern Italian industry. International journal of obesity. 27 (11): 1353-1358.
8. Gu MJK, et al. 2012. Long work hours and adiposity among police officers in a US northeast city. Journal of occupational and environmental medicine. 54 (11): 1374.
9. Ishizaki M, et al. 2004. The influence of work characteristics on body mass index and waist to hip ratio in Japanese employees. Industrial health. 42 (1): 41-49.
10. Kim M-J, et al. 2013. Association between shift work and obesity among female nurses: Korean Nurses’ Survey. BMC public health. 13 (1): 1204.
11. Knutsson A 2003. Health disorders of shift workers. Occupational medicine. 53 (2): 103-108.
12. Lemke MK, Hege A, Perko M, Sönmez S & Apostolopoulos Y 2015. Work patterns, sleeping hours and excess weight in commercial drivers. Occupational medicine. 65 (9): 725-731.
13. Lowden A, Moreno C, Holmbäck U, Lennernäs M & Tucker P 2010. Eating and shift work—effects on habits, metabolism, and performance. Scandinavian journal of work, environment & health. 36 (2): 150-162.
14. Macagnan J, et al. 2012. Impact of nightshift work on overweight and abdominal obesity among workers of a poultry processing plant in southern Brazil. Chronobiology international. 29 (3): 336-343.
15. Magee CA, Caputi P & Iverson DC 2011. Short sleep mediates the association between long work hours and increased body mass index. Journal of behavioral medicine. 34 (2): 83-91.
16. Manenschijn L, van Kruysbergen RG, de Jong FH, Koper JW & van Rossum EF 2011. Shift work at young age is associated with elevated long-term cortisol levels and body mass index. Journal of clinical endocrinology & metabolism. 96 (11): E1862-E1865.
17. Marqueze EC, Ulhôa MA & Moreno CRdC 2013. Effects of irregular-shift work and physical activity on cardiovascular risk factors in truck drivers. Revista de saude publica. 47 (3): 497-505.
18. Peplonska B, Bukowska A & Sobala W 2015. Association of rotating night shift work with BMI and abdominal obesity among nurses and midwives. PLoS One. 10 (7): e0133761.
19. Samara D, Merijanti LT, Tandean R & Harrianto R 2016. The association between shift work and body mass index among female nurses. Universa medicina. 27 (2): 72-77.
20. Scott E, Carter A & Grant P 2008. Association between polymorphisms in the Clock gene, obesity and the metabolic syndrome in man. International journal of obesity. 32 (4): 658.
21. Suwazono Y, et al. 2008. A longitudinal study on the effect of shift work on weight gain in male Japanese workers. Obesity. 16 (8): 1887-1893.
22. Tada Y, et al. 2014. Association of body mass index with lifestyle and rotating shift work in Japanese female nurses. Obesity. 22 (12): 2489-2493.
23. Van Drongelen A, Boot CR, Merkus SL, Smid T & Van Der Beek AJ 2011. The effects of shift work on body weight change—a systematic review of longitudinal studies. Scandinavian journal of work, environment & health. 37 (4): 263-275.
24. Wang X, Armstrong M, Cairns B, Key T & Travis R 2011. Shift work and chronic disease: the epidemiological evidence. Occupational medicine. 61 (2): 78-89.
25. World Health Organization 2004. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 363 (9403): 157-163.
26. World Health Organization 2011. Waist circumference and waist-hip ratio: Report of a WHO expert consultation, Geneva, 8-11 December 2008.

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