Occupational Medicine Advance Access originally published online on November 2, 2005
Occupational Medicine 2006 56(2):83-88; doi:10.1093/occmed/kqi178
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A longitudinal study of the influence of shift work on serum uric acid levels in workers at a telecommunications company
Department of Occupational and Environmental Medicine, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuohku, Chiba 260-8670, Japan
Correspondence to: Mirei Uetani, Department of Occupational and Environmental Medicine, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuohku, Chiba 260-8670, Japan. e-mail: muetani{at}faculty.chiba-u.jp
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Abstract |
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Background Hyperuricemia is a lifestyle-related disease. Although there have been many previous reports about the association of serum uric acid (UA) levels with lifestyle, including eating habits and alcohol intake, there has been no report of a longitudinal study of the relationship between serum UA levels and shift work.
Aims To clarify the influence of shift work on serum UA levels in Japanese workers.
Methods This was a 4-year cohort study of 15 871 workers at a telecommunications company. Pooled logistic regression analyses by sex were performed, with job schedule type, age, body mass index (BMI), lifestyle and the results of blood chemistries as covariates.
Results In males, shift work, part-time work, BMI, consumption of alcohol (less than twice per week, two to five times per week or more than five times per week) and little preference for vegetables were positively associated with the development of increased serum UA (
8 mg/dl in males, 6 mg/dl in females). In females, age, BMI and a history of smoking were positively associated with the development of increased serum UA.
Conclusion This study revealed that shift work is independently related to increased serum UA in males.
Keywords Lifestyle; longitudinal study; occupational health; pooled logistic regression analysis; shift work, uric acid; working conditions
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Introduction |
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Several recent studies have indicated that shift work, including night work, is associated with an increased risk of cerebrovascular disease and coronary artery disease [1–8]. On the other hand, lifestyle-related diseases, which are affected by changes in lifestyle, excessive stress and an increase in consumption of a high-fat diet, are creating serious problems, mainly in developed nations. Hyperuricemia is a lifestyle-related disease that is also thought to be related to metabolic syndrome and insulin-resistance syndrome, which are considered to be risk factors for coronary artery disease [9,10]. Fang and Alderman [11] reported that hyperuricemia is independently and significantly associated with the risk of cardiovascular mortality, and Tomita et al. [12] reported that hyperuricemia has a strong and independent association with relative risks of death from all causes, including coronary heart disease and cancer. Although there have been many previous reports about the association of serum uric acid (UA) levels with lifestyle, including eating habits and alcohol intake, there has been no report of a longitudinal study of the relationship between serum UA levels and shift work. Working conditions may be difficult for an individual to control. The aim of our study was to investigate the association between hyperuricemia and shift work.
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Methods |
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The study was conducted at nine offices of a telecommunications company in the Kanto district of Japan. All workers at this company undergo a legally required health examination once a year. Workers who are 40 years of age or older have an annual blood test. At the same time, a self-administered questionnaire was administered to obtain information about sex, age, past history of disease, present illness, working conditions and lifestyle. Between 1992 and 1996, 50 421 workers aged 40–54 years received annual health check-ups. Workers with a past history or present case of malignant neoplasm, cardiovascular, liver, kidney, respiratory, or collagen disease, metabolic disorder or other disease, or missing body mass index (BMI) and those who did not answer all the questions in an appropriate manner were excluded from the analysis. Metabolic disorders consisted of thyroid disease, diabetes mellitus, hyperlipidemia and gout. Based on the above criteria, 34 550 workers were excluded. The study subjects were 12 246 male and 3625 female workers. The study protocol was approved by the ethical review boards of the Graduate School of Medicine, Chiba University.
Items on the questionnaire regarding working conditions included shift pattern, daily working hours, monthly holidays and one-way commuting time. Items regarding lifestyle included consumption of alcohol, smoking habits, daily sleeping hours, physical exercise, eating three meals a day, eating within 1 h before sleep and preferences for salty meals, fatty meals or vegetables. These items were selected by referring to previous studies and they were categorized as in those studies [13,14]. The shift pattern was categorized into four groups: day workers, shift workers, part-time workers and others. ‘Others’ refers to night workers and other shift patterns that did not correspond to the other three categories. The categories were chosen in consideration of general Japanese working conditions and general lifestyle.
The period of observation continued only as long as the subjects received annual health check-ups. Serum UA was measured with the uricase–peroxidase reaction.
Internal quality control was performed during every measurement period. Increased serum UA was defined as 8 mg/dl in males and 6 mg/dl in females. These cut- off values corresponded to 95% upper limit values of the subjects at entry year. Pooled logistic regression analyses by sex were performed with age, BMI, working conditions and lifestyle as independent variables and the development of increased serum UA as a dependent variable adjusted for the time period. Each examination interval of 1 year was treated as a mini follow-up study. When the subject developed increased serum UA during follow-up, subsequent data were excluded from the analyses. When there were missing data, subsequent data were similarly excluded. The analyses were performed with SPSS 10.0J software (SPSS Japan Inc.). P-values <0.05 were considered to be statistically significant.
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Results |
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Table 1 shows the number of subjects and person-years observed. The mean observed years per person were 2.22 in males and 2.11 in females. The total person-years of observation amounted to 27 146 in males and 7654 in females. In the first observed year, 584 male subjects and 111 female subjects developed increased serum UA.
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Table 2 shows the numbers and percentages of each item in the entry year. Table 3 shows the odds ratios (ORs) and 95% confidence intervals (95% CIs) of the OR in the pooled logistic regression analyses.
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In males, the ORs for shift workers, part-time workers, BMI, drinking alcohol (less than twice per week, two to five times per week or more than five times per week) and little preference for vegetables were significantly higher than those of the respective reference categories. The ORs for age, sleeping <5 h and moderate preference for salty meals were significantly lower than those of the respective reference categories. In males, we tested whether the interaction terms between preference for shift work and other significant factors (age, BMI, consumption of alcohol, sleeping hours, preference for salty meals, preference for vegetables) could be included in the model by forward stepwise selection methods using the Wald statistic and likelihood ratio. As a result, none of these interaction terms was selected to improve the logistic regression model by either method. Thus, we believe that these interactions did not need to be taken into consideration.
In females, the ORs for age, BMI and history of smoking were significantly higher than those of the respective reference categories. The OR for a 60- to 90-min one-way commute was significantly lower than that of the reference category.
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Discussion |
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Our study found that shift pattern, both working shifts and part-time work, was associated with the onset of hyperuricemia, both independently and significantly, in males. We did not find an association between shift pattern and UA levels in females, and smoking did not predict the onset of hyperuricemia.
The average observation period of 
2 years in our study was short. While this could be a weakness of our study, overall this was a large longitudinal study that enrolled 15 871 subjects and therefore should be large enough to obtain meaningful results.
Other studies have investigated the association between shift work and serum UA. Theorell and Akerstedt [15] measured changes in serum UA in two groups of railway workers (n = 16 and n = 17) during a 3-week period of shifts between day and night work. In the group that shifted from day work to night work, serum UA increased significantly after 3 weeks compared to their values before they began night work. In the group that shifted from night work to day work, serum UA decreased significantly in 3 weeks compared to their values right after they stopped working at night. Orth-Gomer [16] observed changes in serum UA in two groups of 23 policemen before and after two different kinds of shift work for 4 weeks each. The customary schedule of rotation was called counter-clockwise rotation. In the new schedule, the rotation of shifts was reversed from counter-clockwise to clockwise, which was theoretically better adapted to spontaneous circadian rhythm but they did not have significant changes in serum UA levels.
It has been thought that shift work has various influences on the human body by interfering with the circadian rhythm [17]. In two other studies night workers were found to have higher levels of catecholamine, a stress hormone, than day workers [15], and the other showed that stress increased serum UA [18]. Therefore a possible mechanism for alterations in serum UA could be that shift work, including night work, elevates serum UA due to a stress increase. However, it is unclear how shift work is associated with the onset of hyperuricemia and further study, including a pathophysiological approach, is needed.
We found a significantly high OR for hyperuricemia in male part-time workers, although the number of subjects was small (n = 11). This might be a healthy worker effect and may not be seen in women if they change their work patterns for social rather than health reasons. We did not find a relationship between shift work and hyperuricemia in females, which suggests that the influence of work style on serum UA is different between males and females. This may be because serum UA in males is more changeable than it is in females. Large epidemiological studies have shown that serum UA is lower in females than in males by 1.0 mg/dl [19–21], and there is a report that patients with gout excrete low levels of dehydroepiandrosterone (DHA) [22]. DHA is a precursor of androgen and it suppresses activity of glucose-6-phosphate dehydrogenase (G-6-PD). There is a presumption that a lack of DHA increases G-6-PD activity and that asthenia of biosynthesis of UA occurs [22]. Also, there are reports that serum UA levels decrease during pregnancy [23] and that long-term administration of synthetic estrogen to transsexual males increases UA clearance in the kidney [24]. Based on these reports, it is suggested that estrogen increases UA excretion and decreases serum UA levels; the difference in the amount of UA production and excretion by gonadal hormones influences differences in serum UA levels between males and females, and it is thought that this influence is the major contributing factor to sexual differences in the association between work style and UA level.
There have been several reports about the relationship between smoking and serum UA. Lellouch et al. [25] and Nakanishi et al. [26] performed longitudinal studies, and Goldbourt and Medalie [27] and Slater et al. [28] performed cross-sectional studies. Each of them showed that there was a negative association between smoking and serum UA level. However, our longitudinal study with a pooled logistic regression analysis did not reveal such an association but previous longitudinal studies have not considered changes in lifestyle during the observation period as we did.
In general, eating and exercise habits are thought to be important to an individual's lifestyle. However, the results of the present study suggest that it is necessary to consider working conditions as a part of lifestyle to prevent the onset of hyperuricemia. It may be difficult for workers to control their working conditions. Occupational health professionals may need to actively consider this in the management of lifestyle-related diseases.
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Conflicts of interest |
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None declared.
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References |
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- Alfredsson L, Karasek R, Theorell T. Myocardial infarction risk and psychosocial work environment: an analysis of the male Swedish working force. Soc Sci Med 1982;16:463–467.
- Alfredsson L, Spetz CL, Theorell T. Type of occupation and near-future hospitalization for myocardial infarction and some other diagnoses. Int J Epidemiol 1985;14:378–388.
[Abstract/Free Full Text] - Knutsson A, Akerstedt T, Jonsson BG et al. Increased risk of ischemic heart disease in shift workers. Lancet 1986;2:89–92.[CrossRef][ISI][Medline]
- Frese M, Semmer N. Shift work, stress and psychosomatic complaints: a comparison between workers in different shift work schedules, non-shift workers and former shift workers. Ergonomics 1986;29:99–114.[Medline]
- Knutsson A, Akerstedt T, Jonsson BG. Prevalence of risk factors for coronary artery disease among day and shift workers. Scand J Work Environ Health 1988;14:317–321.[ISI][Medline]
- Tenkanen L, Sjoblom T, Harma M. Joint effect of shift work and adverse life-style factors on the risk of coronary heart disease. Scand J Work Environ Health 1998;24:351–357.[ISI][Medline]
- Knutsson A, Hallquist J, Reuterwall C et al. Shift work and myocardial infarction: a case-control study. Occup Environ Med 1999;56:46–50.[Abstract]
- Sakata K, Suwazono Y, Harada H et al. The relationship between shift work and the onset of hypertension in male Japanese workers. J Occup Environ Med 2003;45:1002–1006.[ISI][Medline]
- Rathmann W, Funkhouser E, Dyer AR et al. Relations if hyperuricemia with the various components of the insulin resistance syndrome in young black and white adults: the CARDIA study. Coronary Artery Risk Development in Young Adults. Ann Epidemiol 1998;8:250–261.[CrossRef][ISI][Medline]
- Bonora E, Targher G, Zenere MB et al. Relationship of uric acid concentration to cardiovascular risk factors in young men. Role of obesity and central fat distribution. Int J Obes Relat Metab Disord 1996;20:975–980.[ISI][Medline]
- Fang J, Alderman MH. Serum uric acid and cardiovascular mortality the NHANES I epidemiologic follow-up study, 1971–1992. J Am Med Assoc 2000;283:2404–2410.
[Abstract/Free Full Text] - Tomita M, Mizuno S, Yamanaka H et al. Does hyperuricemia affect mortality? A prospective cohort study of Japanese male workers. J Epidemiol 2000;10:403–409.[ISI][Medline]
- Belloc NB, Breslow L. Relationships of physical health status and health practices. Prev Med 1972;1:409–421.[CrossRef][Medline]
- Hagihara A, Morimoto K. Personal health practices and attitudes toward nonsmokers' legal rights in Japan. Soc Sci Med 1991;33:717–721.
- Theorell T, Akerstedt T. Day and night work: changes in cholesterol, uric acid, glucose and potassium in serum and in circadian patterns of urinary catecholamine excretion. A longitudinal cross-over study of railway workers. Acta Med Scand 1976;200:47–53.[ISI][Medline]
- Orth-Gomer K. Intervention on coronary risk factors by adapting a shift work schedule to biologic rhythmicity. Psychosom Med 1983;45:407–415.
[Abstract/Free Full Text] - Halberg F. Biological rhythms. In: Hedlund LW, Franz JM, Kenny AD, eds. Biological rhythms and endocrine function. Advances in Experimental Medicine and Biology. Vol. 4. New York: Plenum Press; 1975.
- Clark DA, Arnold EL, Foulds EL Jr. Serum urate and cholesterol levels in Air Force Academy cadets. Aviat Space Environ Med 1975;46:1044–1048.[Medline]
- Mikkelsen WM, Dodge HJ, Valkenburg H. The distribution of serum uric acid values in a population unselected as to gout or hyperuricemia: Tecumseh, Michigan, 1959–1960. Am J Med 1965;39:242–251.[CrossRef][ISI][Medline]
- Nhonoli AM, Kihama F. Serum uric acid values in Tanzanian rural communities. Trop Geogr Med 1974;26:283–288.[ISI][Medline]
- Akizuki S. Serum uric acid levels among thirty-four thousand people in Japan. Ann Rheum Dis 1982;41:272–274.
[Abstract/Free Full Text] - Sparagana M, Phillips G. Dehydroepiandrosterone (3-hydroxy-5-androsterone-17-one) metabolism in gout. Steroids 1972;19:477–492.[CrossRef][ISI][Medline]
- Doyle JA, Camphell S, Duncan AM. Serum uric acid levels in normal pregnancy with observations on the renal excretions of urate in pregnancy. J Clin Pathol 1966;19:501–503.
[Abstract/Free Full Text] - Nicholls A, Snaith ML, Yablonsly H. Effect of stilboesterol on levels of uric acid in plasma and urine. Ann Rheum Dis 1973;32:386–387.
[Free Full Text] - Lellouch J, Schwartz D, Tran MH. The relationship between smoking and levels of serum urea and uric acid. Results of epidemiological survey. J Chronic Dis 1969;22:9–15.[CrossRef][ISI][Medline]
- Nakanishi N, Tatara K, Nakamura K et al. Risk factors for the incidence of hyperuricemia: a 6-year longitudinal study of middle-aged Japanese men. Int J Epidemiol 1999;28:888–893.
[Abstract/Free Full Text] - Goldbourt U, Medalie JH. Characteristics of smokers, non-smokers and ex-smokers among 10,000 adult males in Israel II. Physiologic, biochemical and genetic characteristics. Am J Epidemiol 1977;105:75–86.
[Abstract/Free Full Text] - Slater PE, Kaufmann NA, Friedlander Y et al. Effects of smoking and physical activity on serum uric acid in a Jerusalem population sample. Ann Hum Biol 1985;12:179–184.[CrossRef][ISI][Medline]
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