objective: This study compared the effect of alternating shift work and day work on weight gain in Japanese male workers. Methods and Procedures: A longitudinal cohort study was conducted in day workers (n = 4,328) and alternating shift workers (n = 2,926) of a steel company who received annual health checkups over a 14-year period between 1991 and 2005. The association between the type of job schedule and weight gain was investigated using multivariate pooled logistic regression analyses. The endpoints in the study were either a 5, 7.5, or 10% increase in BMI during the period of observation, compared to the BMI at entry. Results: The type of job schedule was significantly associated with all three BMI endpoints (5% increase in BMI; odds ratio (OR) for comparison between alternating shift workers and regular day workers, 1.14; 95% confidence interval (CI), 1.06-1.23): (7.5% increase in BMI; OR, 1.13; 95%CI, 1.03-1.24: 10% increase in BMI; OR, 1.13; 95%CI, 1.00-1.28). BMI at study entry was also positively associated with the 5, 7.5, and 10% increases in BMI during the study. On the other hand, age and drinking habits were negatively associated with 5, 7.5, and 10% increases in BMI. Discussion: Our study revealed that alternating shift work was an independent risk factor for weight gain in male Japanese workers. Efficient health screening and regular checkups, combined with support to control unhealthy lifestyle factors, would be of considerable benefit for maintaining the health of Japanese shift workers.

Abstract-To clarify the effect of shift work on blood pressure in Japanese men, a 14-year historical cohort study was conducted in day workers (nϭ3963) and alternating shift workers (nϭ2748) who received annual health checkups between 1991 and 2005 in a Japanese steel company. The end points were a Ն10%, Ն15%, Ն20%, Ն25%, or Ն30% 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, ␥-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: Ն10%, 1.15 (1.07 to 1.23); Ն15%, 1.21 (1.12 to 1.31); Ն20%, 1.15 (1.04 to 1.28); Ն25%, 1.20 (1.06 to 1.37); and Ն30%, 1.23 (1.03 to 1.47) for systolic blood pressure and Ն10%, 1.19 (1.11 to 1.28); Ն15%, 1.22 (1.13 to 1.33); Ն20%, 1.24 (1.13 to 1.37); and Ն25%, 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.

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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, gamma-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 (> or =10% HbA1c increase, odds ratio 1.35 [95% confidence interval 1.26-1.44]; > or =15% HbA1c increase, odds ratio 1.29 [95% confidence interval, 1.19-1.40]; > or =20% HbA1c increase, odds ratio 1.23 [95% confidence interval 1.11-1.37]; and > or =25% HbA1c increase, odds ratio 1.19 [95% confidence interval 1.03-1.36]). Age, body mass index, alanine aminotransferase, and gamma-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.