Diana1 72 Department of Occupational Medicine, Medical Faculty, Trisakti University Correspondence adr. Diana Samara, MKK Department of Occupational Medicine, Medical Faculty, Trisakti University Jl. Kyai Tapa 260 - Grogol Jakarta 11440 Telp 021-5672731 ext.2802 Email : davidwp@cbn.net.id Univ Med 2008; 27: 72-7. The association between shift work and body mass index among female nurses April-June 2008April-June 2008April-June 2008April-June 2008April-June 2008 Vol.27 - No.2 Vol.27 - No.2 Vol.27 - No.2 Vol.27 - No.2 Vol.27 - No.2 ABSTRACT UNIVERSA MEDICINA Diana Samaraa, Lie T. Merijanti, Reza Tandean, and Ridwan Harrianto Possibly due to a disturbance of biological rhythms, shift work is associated with several health problems, particularly an increased risk of coronary heart disease (CHD). Obesity is a well known independent cardiovascular risk factor and has been shown to be more prevalent among shift workers. The objective of this study was to examine the association between shift work and body mass index in nurses working in one hospital in Central Jakarta. A cross-sectional study was conducted among 152 female nurses, ranging from 22 to 55 years of age, with determination of body mass index (BMI), and systolic and diastolic blood pressure (SBP and DBP). The results show a mean age of 30.9 ± 7.2 years and mean job experience of 8.9 ± 7.6 years. There was no significant difference in the prevalence of gastrointestinal disorders between shift and day workers. Mean BMI (23.1 ± 3.6) and mean job experience (6.9 ± 5.9 years) in shift nurses were significantly different from those in day workers (BMI = 24.8 ± 3.8; job experience 15.4 ± 8.4 years). In shift working nurses the BMI increased significantly in proportion to job experience (p=0.014). In conclusion, the present study has proven that job experience significantly increased BMI in shift working nurses. Keywords : Shif work, body mass index, job experience, female nurses INTRODUCTION S h i f t w o r k c a n b e d e f i n e d a s w o r k performed outside the normal daylight hours. Shiftwork has been empirically linked to a variety of diseases, although evidence does not suggest an effect on all-cause mortality.(1) Three p a t h w a y s h a v e b e e n i m p l i c a t e d i n t h e relationship between shiftwork and disease: (i) disruption of circadian rhythms (leading to sleep/ wake disturbances, desynchronization of internal processes, and increased susceptibility to disease); (ii) disturbed socio-temporal patterns (resulting from atypical work hours leading to 73 Univ Med Vol.27 - No.2 family problems, reduced social support, and stress); and (iii) unfavorable changes in health behaviors (increased smoking, poor diet, and irregular meals).(2) Many workers complain of g a s t r o i n t e s t i n a l p r o b l e m s r e s u l t i n g f r o m irregularly timed meals and poor quality of food, as well as increased consumption of soft drinks and caffeine-containing beverages.(3,4) Circadian disturbances affecting the intake, digestion, and absorption of food are thought to play a major etiological role, but loss of sleep, fatigue, and the social stress of shiftwork may also be implicated. Typically, shift workers have h i g h e r l e v e l s o f g a s t r i c s y m p t o m s ( e . g . indigestion, heartburn, constipation, loss of appetite, and nausea) than day workers, even with control for demographic, job, and lifestyle variables.(5) Gastrointestinal disorders are more common in shift workers, who complain of abdominal pain and alteration in bowel habit. There is strong evidence linking shift work to peptic ulcer disease and in lesser degree to c o r o n a r y h e a r t d i s e a s e . ( 6 ) S h i f t w o r k i s associated with an increased risk of coronary heart disease (CHD), as reported in several studies performed on shift workers.(7) Obesity is a well known independent cardiovascular risk factor, and interestingly, it has been shown to be more prevalent among shift workers.(8) Similarly, a more marked weight gain has been reported in shift-working subjects.(9-11) Obesity suffer from a high risk of insulin resistance and its metabolic complications, such as type 2 diabetes mellitus, hypertriglyceridemia, low levels of high density lipoprotein cholesterol, and hypertension.(12) Shift work is the most widely used tool of working time organization, as it enables round-the-clock activities not only in relation to rigid technological conditioning (e.g. chemical and steel industries, power plants) and necessary social services (e.g. h e a l t h s e r v i c e s , t r a n s p o r t , e l e c t r i c i t y, telecommunications), but also to support of productive and economic choices (e.g. textile, paper, food, mechanical industry, banking). In the medical field, physicians, nurses and other ancillary staff are expected to be performing their jobs or to be on-call on a 24-hour basis. There have been few studies undertaken in Indonesia on the extent to which shift work is related to health problems among health care workers, and this has been a neglected area in o c c u p a t i o n a l h e a l t h a n d s a f e t y i s s u e s i n hospitals. The objective of the present study was to investigate the association between shift work schedules and health problems, particularly body mass index (BMI). METHODS Research design A cross-sectional study was conducted during Februari – April 2007. Study subjects T h e p a r t i c i p a n t s w e r e f e m a l e n u r s e s working in one hospital in Central Jakarta. From a total of 187 female nurses employed by the h o s p i t a l , 1 5 2 h e a l t h y n u r s e s ( f r e e o f gastrointestinal disorders) participated in this study. Thirty five nurses were excluded because of gastrointestinal disorders. Data collection The investigators explained the purpose of the research and requested cooperation from e a c h p a r t i c i p a n t . A n a n o n y m o u s s e l f - administrated questionnaire was used to collect the required data from each participant. The distribution and collection of questionnaires was performed through the head nurse. The items included in the questionnaire related to subject characteristics, e.g. age, gender, education, marital status, working unit, job experience, and working system (day worker/shift worker). In this study, shiftwork was defined as any regular 74 employment outside the usual working hours, defined arbitrarily to be between 08.00 hours and 16.00 hours. For gastrointestinal problems, several questions were combined into one, e.g. “Which one of the following problems have you experienced continuously?”, viz. decreased appetite, constipation, diarrhoea, nausea, peptic ulcer, indigestion and eructation. Measurements Systolic and diastolic blood pressure (SBP and DBP) readings were recorded to the nearest 5 m m o f m e r c u r y a s t h e m e a n o f t w o measurements with the subjects seated, using a m e r c u r y s p h y g m o m a n o m e t e r w i t h a n appropriate cuff size. Hypertension was defined according to WHO criteria.(13) Body weight was measured using the SEGA portable scale and recorded to the nearest 0.1 kg. Height was measured on barefooted subjects to the nearest c e n t i m e t e r u s i n g t h e m i c r o t o i s . B M I w a s calculated as weight in kilograms divided by the s q u a r e o f h e i g h t i n m e t e r s . F o r A s i a n populations, BMI is classified into the following categories: underweight (<18.5 kg/m2), normal (18.5–22.9 kg/m2), overweight (23.0–27.5 kg/ m2), and obese (≥ 27.6 kg/m2).(14) Statistical analysis Statistical analyses were performed using SPSS version 10.0 and Epi Info 2000. The chi- squared test was used to assess univariate associations between shift variables and reported problems, and Student’s t test for comparing continuous variables. Analysis of variance was applied for comparing BMI and duration of job experience. The level of statistical significance was set at 0.05. RESULTS Table 1 summarizes the characteristics of the participating nurses. The mean age was 30.9 ± 72.2 years, 91 nurses (59.9%) were married and mean job experience was 8.9 ± 7.6 years. Since only 2.6% of the nurses had a degree or higher qualification, the study population could not be regarded as being highly educated. Approximately 76.3% (116/152) of the nurses were engaged in a rotating shift schedule. Table 2 presents the reported prevalence of shiftwork-related gastrointestinal problems, in which the difference in prevalence between shift a n d d a y w o r k e r s d i d n o t r e a c h s t a t i s t i c a l significance (p > 0.05). Mean SBP and DBP were not significantly different between shift workers and day workers. The mean BMI in the group of shift workers was significantly lower (23.1 ± 3.6) compared with the group of day workers (24.8 ± 3.8) (p=0.012). Mean job experience among shift workers was significantly shorter duration (6.9 ± 5.9 years) in comparison with day workers (15.4 ± 8.4 years). (Table 3) Table 1. Characteristics and work pattern of nurses in the hospital under study (n = 152) Samara, Merijanti, Tandean, et al Shift work and body mass index 75 Univ Med Vol.27 - No.2 Table 2. Prevalence of shiftwork-related gastrointestinal problems reported among the nurses T h e s e d a t a w e r e s u b j e c t e d t o f u r t h e r analysis to determine the influence of job experience on BMI, by using one-way analysis o f v a r i a n c e a n d Tu c k e y H S D m u l t i p l e comparison. One-way analysis of variance determined the values of BMI distributed for classes of job experience in day workers and shift w o r k e r s . O n a v e r a g e t h e B M I i n c r e a s e d significantly with job experience in the shift workers (p=0.014), but not in the day workers (p=0.644). (Table 4) The Tuckey HSD multiple comparison showed that the mean difference (-3.2613) was statistically significant between nurses with job experience of less than 5 years and 16-30 years. (Table 5) Table 3. Comparison of the continuous variables age, job experience, BMI, SBP, and DBP between day and shift workers Table 4. Means and SD of BMI distributed for classes of job experience in day workers and shift workers (152 subjects) 76 DISCUSSION This study has demonstrated that mean BMI was lower in shift workers than in day workers. However, after adjustment for job experience, the BMI was significantly higher in shift workers compared with day workers. The results are in agreement with the study done by Karlssona et al,(8) indicating a significantly higher BMI in shift workers in comparison with non-shift workers. Obesity was also more common in shift workers than in day workers. A longitudinal observational study among 469 nurses aged 21- 58 years showed that exposure to night work can l e a d t o w e i g h t g a i n a n d o v e r w e i g h t . ( 11 ) Essentially identical results were obtained in offshore workers, viz. that continued exposure to day-night shift work gives rise to increased BMI. Another study on shift workers revealed the ocurrence of weight gain, where body weight in shift workers increased 4.3 kg as compared with 0.9 kg in day workers (p=0.02).(15) There was a tendency for shift workers to report eating more and taking more naps than did the day workers. A cohort study on 377 shiftworkers and non- s h i f t w o r k i n g c o n t r o l s s h o w e d a p o s i t i v e relationship between BMI and waist-to-hip ratio (WHR) in comparison to duration of shiftwork experience, with adjustment for age.(16) The study undertaken by Di Lorenzo et al. on 319 workers in Southern Italy indicated that shift work was responsible for excessive body mass index.(17) However, Nakamura et al(18) did not find any difference in body weight when comparing day workers and shift workers, although workers i n a t h r e e - s h i f t r o t a t i o n h a d a n i n c r e a s e d abdominal to hip ratio, indicating a higher proportion of central obesity among shift workers. A possible explanation for these findings could be insufficient adjustment for p o s s i b l e c o n f o u n d i n g v a r i a b l e s , s u c h a s socioeconomic factors. Another possibility is that the duration of follow-up could influence the change in body weight as suggested by Karlsson.(8) Shift workers commonly have a disturbed appetite dan tend to disregard food quality and quantity; they tend to consume “junk” food instead of complete nutritionally balanced meals.(19) The present study did not find any differences in prevalence of hypertension b e t w e e n s h i f t a n d d a y w o r k e r s , w h i c h i s consistent with previous studies.(20) The shift system in hospital X, where the nurses were employed, had work shifts of 6 hours duration rotated as follows: the first shift lasted from 08.00 to 14.00 local time, the second from 14.00 until 20.00, and the third w a s f r o m 2 0 . 0 0 t o 0 8 . 0 0 . E a c h s h i f t w a s maintained for 2 days, with one day off after 6 working days. There is still a difference of opinion as to which system is the better one: weekly or twice weekly shifts, as each has its strengths and weaknesses. CONCLUSIONS Shift nurses tend to have a gain in BMI proportional to job experience. However, no significant differences in SBP and DBP were found in shift workers as compared to day workers. Samara, Merijanti, Tandean, et al Shift work and body mass index Table 5. Multiple comparisons of BMI between the class job of experience in the shift workers 77 Univ Med Vol.27 - No.2 ACKNOWLEDGEMENTS This study was supported by the Medical Faculty of Trisakti University. We extend our gratitude to all nurses who participated in this s t u d y, a n d t o D r. M . F a d h i l R a s a d , E N T specialist, as Head of the Center of Education and Training at Tarakan Hospital, Jakarta. REFERENCES 1. Knutsson A. Health disorders of shift workers. 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