In this study, we applied a general linear mixed model to demonstrate the usefulness of multilevel analysis to assess the association between aging and longitudinal blood pressure variations. The study population which was followed between 1997 and 2000 consisted of 5, 574 male employees over the age of 40 from two worksites in Aichi Prefecture. We adopted both the general linear regression model and the general linear mixed model in statistical analyses where systolic and diastolic blood pressures (BP) were regressed by the observation period of one year, with the baseline body mass index, age, preference for salty taste, daily alcohol consumption, smoking status, leisure time physical activity, and family history of hypertension treated as covariates.In the regression model, aging showed a significant relationship with the diastolic BP increase, but not with the systolic BP increase. In the mixed model, aging was found to be a significant predictor of the longitudinal rise in both systolic and diastolic BP. Random-effect analysis showed a significant inverse relationship between baseline BP and the slope of the regression line of longitudinal BP increase. These findings suggested that the effects of the regression to the mean could be separated at the upper level in the hierarchical model, thus resulting in improvement of the statistical power. We concluded that multilevel modeling was a useful approach to effectively detect the relationship of aging with longitudinal BP variations.

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To assess the validity of a simple 4-point scale of perceived mental stress, we analyzed relationships of perceived mental stress with 6 job stressors : demand, control, skill underutilization, workplace human relations, physical environment, and job satisfaction. We also examined the association of lifestyle with perceived mental stress. Study subjects were 5, 159 male and 1, 468 female Japanese workers aged 35 years and above in 2002. Awareness of stress was assessed by the question : “Do you have much stress in your life?”, and participants were asked to select one among 4 responses : 'very much', 'much', 'ordinary', or 'little'. Six job stressors were assessed by a Simple Questionnaire Concerning Work Related Stress.
There were positive associations between perceived mental stress and all 6 job stressors in men, and 5 job stressors except skill underutilization in women. Therefore, we considered that a simple 4-point scale of perceived mental stress was reliable to evaluate individual stress.
The subjects with highly perceived stress were more likely to have shift time or midnight work, and to have overtime work. The sleep duration on weekdays tended to decrease, the proportion of subjects with two or more sleep-related complaints tended to increase, and physical activity tended to decrease according to the increase in the level of perceived stress. The proportion of subjects who lacked confidants, and who lost ikigai (subjective well-being) was linearly associated with an increased level of perceived stress. Perceived mental stress has a reasonable association with the individual's daily mental and physical stress reaction and coping, as well as social support.

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