Kumihiko Tanaka

A Longitudinal Study on the Effect of Shift Work on Weight Gain in Male Japanese Workers

Objective: This study compared the effect of alternating shift work and day work on weight gain in Japanese male workers.

Shift Work Is a Risk Factor for Increased Blood Pressure in Japanese Men. A 14-Year Historical Cohort Study

To clarify the effect of shift work on blood pressure in Japanese men, a 14-year historical cohort study was conducted in day workers (n=3963) and alternating shift workers (n=2748) who received annual health checkups between 1991 and 2005 in a Japanese steel company. The end points were a ≥10%, ≥15%, ≥20%, ≥25%, or ≥30% increase in systolic blood pressure or diastolic blood pressure from baseline during the period of observation. The association between shift work and an increase in blood pressure was investigated adjusting for age, body mass index, hemoglobin A1c, total serum cholesterol, creatinine, aspartate aminotransferase, &ggr;-glutamyl transpeptidase, uric acid, drinking habit, smoking habit, and habitual exercise by multivariate pooled logistic regression analyses. Shift work was significantly associated with the various end points. The odds ratios (and 95% CIs) were as follows: ≥10%, 1.15 (1.07 to 1.23); ≥15%, 1.21 (1.12 to 1.31); ≥20%, 1.15 (1.04 to 1.28); ≥25%, 1.20 (1.06 to 1.37); and ≥30%, 1.23 (1.03 to 1.47) for systolic blood pressure and ≥10%, 1.19 (1.11 to 1.28); ≥15%, 1.22 (1.13 to 1.33); ≥20%, 1.24 (1.13 to 1.37); and ≥25%, 1.16 (1.03 to 1.30) for diastolic blood pressure. Our study in male Japanese workers revealed that alternating shift work was a significant independent risk factor for an increase in blood pressure. Moreover, the effect of shift work on blood pressure was more pronounced than other well-established factors, such as age and body mass index.

SHIFTWORK AND IMPAIRED GLUCOSE METABOLISM: A 14-YEAR COHORT STUDY ON 7104 MALE WORKERS

The aim of this study was to assess the effect of shiftwork on hemoglobin A1c (HbA1c) level, as an index of glucose metabolism. A 14 yr prospective cohort study was conducted on day (n = 4219) and alternating shiftworkers (n = 2885) who received annual health checkups between 1991 and 2005 at a Japanese steel company. The endpoints were either a 10%, 15%, 20%, 25%, or 30% increase in HbA1c during the period of observation, compared to HbA1c at entry to the study. The association between the type of job schedule and increase in HbA1c was investigated after adjusting for age, body mass index, mean arterial pressure, total serum cholesterol, creatinine, alanine aminotransferase, γ-glutamyl transpeptidase, uric acid, drinking habit, smoking habit, and habitual exercise using multivariate pooled logistic regression analyses. Shiftwork was significantly associated with the various HbA1c endpoints (≥10% HbA1c increase, odds ratio 1.35 [95% confidence interval 1.26–1.44]; ≥15% HbA1c increase, odds ratio 1.29 [95% confidence interval, 1.19–1.40]; ≥20% HbA1c increase, odds ratio 1.23 [95% confidence interval 1.11–1.37]; and ≥25% HbA1c increase, odds ratio 1.19 [95% confidence interval 1.03–1.36]). Age, body mass index, alanine aminotransferase, and γ-glutamyl transpeptidase were associated positively with all five HbA1c endpoints. Uric acid was associated negatively with all five HbA1c endpoints. Our study on male Japanese workers revealed alternating shiftwork (in addition to other established factors, such as age and body mass index) was a consistent risk factor for impaired glucose metabolism.

Shift work is a risk factor for increased total cholesterol level: a 14-year prospective cohort study in 6886 male workers

Objectives: The widespread adoption of 24 h continuous operations in a number of industries has resulted in an increase in shift work, which may influence lipid metabolism because of disturbed circadian rhythms, broken sleep and lifestyle problems. The objective of the present study was to assess the effect of shift work on serum total cholesterol as an index of lipid metabolism. Methods: A 14-year prospective cohort study was conducted in day workers (n = 4079) and alternating shift workers (n = 2807) who received annual health check-ups between 1991 and 2005 in a Japanese steel company. The end-points were either a 20%, 25%, 30%, 35%, 40% or 45% increase in serum total cholesterol during the period of observation, compared with serum total cholesterol at entry to the study. The association between the job schedule type and increase in serum total cholesterol was investigated using multivariate pooled logistic regression analyses. The odds ratios for the effect of shift work were obtained after adjustment for a number of potential confounders. Results: The significant odds ratios of alternating shift work (and 95% confidence intervals) were: ⩾20%, 1.16 (1.07 to 1.26); ⩾25%, 1.16 (1.05 to 1.28); ⩾35%, 1.23 (1.05 to 1.43); ⩾40%, 1.30 (1.07 to 1.58); and ⩾45%, 1.28 (1.01 to 1.63) for serum total cholesterol. Conclusion: Generally the odds ratios of alternating shift work tended to be higher for stricter cut-points of relative increase in serum total cholesterol level. Our study in male Japanese workers revealed that alternating shift work adversely affected lipid metabolism.

ESTIMATION OF THE BENCHMARK DURATION OF SHIFTWORK ASSOCIATED WITH WEIGHT GAIN IN MALE JAPANESE WORKERS

The authors estimated the benchmark durations (BMDs) and their 95% lower confidence limit (BMDL) for the reference duration of shiftwork for weight gain. A 14-yr prospective cohort study was conducted in male workers at a Japanese steel company (n = 7254) who had received annual health check-ups between 1991 and 2005. The endpoints in the study were either a 5%, 7.5%, or 10% increase in body mass index (BMI) during the period of observation, compared to the BMI at entry. The association between the duration of shiftwork and weight gain was investigated using multivariate pooled logistic regression analyses with stepwise selection of covariates, including age, BMI measured during the study, drinking and smoking habits, and habitual exercise. The BMDL/BMD for shiftwork in subjects aged in their 40s or ≥50 yrs was estimated using benchmark responses (BMRs) of 5% or 10% and parameters for the duration of shiftwork and other covariates. For workers aged in their 40s, the BMDL/BMD for shiftwork with a BMR of 5% was 18.6/23.0 yrs (≥7.5%) and 16.9/19.4 yrs (≥10%). For workers aged ≥50 yrs, the BMDL/BMD with a BMR of 5% was 22.9/28.2 yrs (≥7.5%) and 20.6/23.6 yrs (≥10%). The reference duration of shiftwork that associated with weight gain was shown to be at least 17 yrs in middle-aged workers. Special attention should be paid to prevent weight gain at an earlier stage and not when this increase in weight has become apparent. (Author correspondence: suwa@faculty.chiba-u.jp)

Benchmark duration of work hours for development of fatigue symptoms in Japanese workers with adjustment for job-related stress.

The objective of this study was to calculate benchmark durations and lower 95% confidence limits for benchmark durations of working hours associated with subjective fatigue symptoms by applying the benchmark dose approach while adjusting for job-related stress using multiple logistic regression analyses. A self-administered questionnaire was completed by 3,069 male and 412 female daytime workers (age 18-67 years) in a Japanese steel company. The eight dependent variables in the Cumulative Fatigue Symptoms Index were decreased vitality, general fatigue, physical disorders, irritability, decreased willingness to work, anxiety, depressive feelings, and chronic tiredness. Independent variables were daily working hours, four subscales (job demand, job control, interpersonal relationship, and job suitability) of the Brief Job Stress Questionnaire, and other potential covariates. Using significant parameters for working hours and those for other covariates, the benchmark durations of working hours were calculated for the corresponding Index property. Benchmark response was set at 5% or 10%. Assuming a condition of worst job stress, the benchmark duration/lower 95% confidence limit for benchmark duration of working hours per day with a benchmark response of 5% or 10% were 10.0/9.4 or 11.7/10.7 (irritability) and 9.2/8.9 or 10.4/9.8 (chronic tiredness) in men and 8.9/8.4 or 9.8/8.9 (chronic tiredness) in women. The threshold amounts of working hours for fatigue symptoms under the worst job-related stress were very close to the standard daily working hours in Japan. The results strongly suggest that special attention should be paid to employees whose working hours exceed threshold amounts based on individual levels of job-related stress.

Dose-response relationship between tobacco or alcohol consumption and the development of diabetes mellitus in Japanese male workers.

BACKGROUND The aim of this study was to examine the dose-response relationships between tobacco or alcohol consumption and the development of diabetes mellitus. METHODS An 8-year prospective cohort study was conducted in 8423 male workers who received annual health check-ups between 2002 and 2010 at a Japanese steel company. The endpoints were defined as an HbA(lc)≥6.1% or taking any anti-diabetic medication. The dose-response relationships of tobacco or alcohol consumption were investigated using a proportional hazards regression with time-dependent covariates selected from baseline age, body mass index, mean arterial pressure, total serum cholesterol, aspartate aminotransferase, creatinine and uric acid, shift work or day work, and habitual exercise by stepwise selection method. RESULTS A positive dose-response relationship between tobacco consumption and the development of diabetes mellitus was observed, with a significantly higher hazard ratio (HR) seen with higher tobacco consumption (11-20 cigarettes/day, HR 1.26 [95% confidence interval (CI), 1.00-1.59], ≥21 cigarettes/day, HR 1.54 [95%CI, 1.20-1.97]). In contrast, we observed a negative dose-response relationship between alcohol consumption and the development of diabetes mellitus, with a significantly lower HR with higher weekly alcohol consumption (7.0-13.9 gou/week [154-307 g/week], HR 0.73 [95% CI, 0.55-0.97], ≥14.0 gou/week [308 g/week], HR 0.75 [95% CI, 0.57-0.98]). CONCLUSIONS The results indicated that decreasing tobacco consumption will achieve significant prevention of diabetes mellitus. On the other hand, we observed a significant, negative dose-response relationship between alcohol consumption and the development of diabetes mellitus, in contrast to previous studies that reported a positive relationship in the Japanese population.

Longitudinal effect of smoking cessation on physical and laboratory findings.

BACKGROUND Detailed information on the expected physiologic changes after smoking cessation is practically useful to encourage people to stop smoking. Furthermore, weight increase after cessation may affect such physiologic changes. PURPOSE This article aims to evaluate the effect of smoking cessation on annual changes in body weight, blood pressure, and blood biochemistry. METHODS This study analyzed the results of annual health examinations from 1991 to 2005 in male Japanese workers in 2009. Subjects classified as stopping smoking (n=445) responded initially as smokers in a self-administered questionnaire (baseline year) and then answered consistently as nonsmokers for 3 subsequent years. Of the 2672 smokers identified in the study, 2403 subjects who had data available for at least 4 successive years were selected as controls. The time course of physiologic and laboratory data was analyzed using a linear mixed model. RESULTS Data adjusted for age, type of job schedule, drinking and physical activity showed that subjects who stopped smoking had significantly greater increases in weight, BMI, systolic and diastolic blood pressure, total cholesterol, high-density lipoprotein cholesterol, and uric acid and a greater decrease in hemoglobin in the 3 years following smoking cessation than continuing smokers. Additional adjustment for change in BMI from baseline negated the significant deterioration in systolic and diastolic blood pressure and total cholesterol that occurred following smoking cessation. CONCLUSIONS Increase in body weight, blood pressure, and blood biochemistry can continue for at least 3 years after smoking cessation. This study also indicated that these increases were related to the weight increase that occurred after smoking cessation.

Effect of high-sensitivity C-reactive protein on the development of diabetes as demonstrated by pooled logistic-regression analysis of annual health-screening information from male Japanese workers

AIM The aim of this study was to determine the relationship between the development of diabetes mellitus and high-sensitivity C-reactive protein (HsCRP) adjusted for various potential confounders. METHODS This 5-year prospective cohort study was conducted at a Japanese steel factory and involved male workers who had received annual health screenings between 2005 and 2010. The 7392 male participants were aged 19-75 years. The study endpoint, the development of diabetes mellitus, was defined as HbA(1c) greater or equal to 6.5% or the use of antidiabetic medication. The association between variables was investigated using pooled logistic regression adjusted for various covariates such as age, baseline body mass index (BMI) and increase in BMI from baseline, blood biochemistry, job schedule and job-related stress. RESULTS The incidence rate of diabetes development per 1000 person-years was 13.9. Multivariate analysis showed a significant relationship between the development of diabetes and elevated levels of baseline HsCRP and increases in levels from baseline. The Odds ratios for a 2.9-fold (±1 geometric standard deviation) increase in baseline HsCRP and increase in HsCRP level from baseline were 1.18 [95% confidence interval (CI): 1.03-1.34; P=0.018] and 1.21 (95% CI: 1.03-1.41; P=0.018), respectively. CONCLUSION The present study has indicated that HsCRP is an independent predictor for the development of diabetes in men, together with various confounders such as BMI, type of job schedule and job-related stress.

Longitudinal evaluation of the effect of smoking initiation on body weight, blood pressure, and blood biochemistry.

OBJECTIVE To evaluate the effect of smoking initiation on annual changes in body weight, blood pressure, and blood biochemistry. METHODS This study analyzed the results of annual health examinations from 1991 to 2005 in male Japanese workers. Subjects who started smoking (n=214) initially responded as non-smokers in a self-administered questionnaire (baseline year) and then answered consistently as smokers for 3 subsequent years. Out of 2547 non-smokers, we selected 1589 controls who had data available for at least four successive years. The time course of physiological and laboratory data was analyzed using a linear mixed model. RESULTS A significant temporal decrease from baseline in body mass index (first year, -0.1 kg/m(2)), diastolic blood pressure (second year, -1.5 mm Hg) and gamma-glutamyl transpeptidase (second year, -3.5 IU/L) was observed for subjects who started smoking. An opposite pattern was observed in non-smokers. On average, those who started smoking had significantly lower body mass index (first year, -0.2 kg/m(2); second year, -0.2 kg/m(2)), systolic blood pressure (second year, -2.1 mm Hg), diastolic blood pressure (second year, -2.0 mm Hg), and gamma-glutamyl transpeptidase (second year, -4.5 IU/L) than non-smokers. CONCLUSION In this study, smoking initiation did not yield clinically significant long-term benefits with respect to physiological or biochemical outcomes. These results are important because few studies have tracked these types of changes longitudinally from initiation through 3 years of follow-up.