Estimated sleep debt and work stress in Japanese white-collar workers.

Sleep debt on weekdays in Japanese white-collar workers, estimated using a questionnaire, was associated with age, overtime, and self-rated workload.

Sympathetic predominance in young male white-collar workers with mild to moderate hypertension.

In order to investigate the difference in diurnal variation of autonomic control between young male mild to moderate hypertensive and normotensive white-collar workers, we accessed heart rate variability with ambulatory blood pressure for over 24 hours including work and sleep periods. Both mean systolic and diastolic blood pressures (SBP and DBP) were significantly (p<0.01) higher in hypertensives (HT, n=11) than normotensives (NT, n=11) in all phases, whereas heart rate was not different between them in any phase. Blood pressures during work period (on-duty) were significantly higher than those during non-work period (off-duty) in both NT and HT. High frequency (HF; 0.15-0.40 Hz) power showed a circadian pattern in phase with the sleep-wake cycle. Both HF and low frequency (LF; 0.05-0.15 Hz) powers in HT were significantly lower than that in NT during the sleep period (p<0.05). LF/HF ratio showed a circadian pattern that was almost opposite of the pattern in HF power. Twenty-four-hour average LF/HF in HT was higher than that in NT (p<0.05). Especially during on-duty, LF/HF in HT was significantly higher than in NT (p<0.05). The increase of SBP and LF/HF from off-duty period to on-duty period (deltaSBP and deltaLF/HF) showed significant positive correlation (r=0.67, P<0.05) in HT group, suggesting that the SBP elevation during on-duty in HT may be coupled with sympathetic activation. These results suggest that HT showed significantly reduced parasympathetic control during sleep and an increased sympathetic activity especially during on-duty as compared with NT. Our findings imply that persistence of sympathodominant states together with reduced vagal activity in young mild to moderate hypertensive workers may be related to future cardiovascular disorders.

Cross-sectional survey on risk factors for insomnia in Japanese female hospital nurses working rapidly rotating shift systems.

A cross-sectional survey was carried out for the purpose of examining the association of work stress with insomnia among nurses working rotating shift systems. A self-administered questionnaire on sleep and mental health was distributed to 875 nurses at five hospitals in Japan. Out of the data from 785 (89.7%) respondents, those from 555 women engaged in rapidly and irregularly rotating shift systems as full-time nurses were examined. The prevalence of insomnia (29.2%) was three to four times higher than that in the general population. Among the insomniacs, 23% were current users of medically prescribed hypnotics. Multiple logistic analysis revealed that being 24 or less years old, working three or less night shifts per month, having six or less non-working days per month, receiving less support from colleagues and superiors, and taking care of severely ill patients were independent risk factors for insomnia. The number of hours of a night shift was found not associated with insomnia, taking the above variables into account. These results suggest that at least three factors, i.e., 1) young nurses not adapted to shiftwork, 2) the nurses requiring to remedy sleep deficits on non-working days, and 3) the work stress partly characteristic of nurses, have an adverse influence on their sleep.

Hematocrit correlates with blood pressure in young male office workers.

High hematocrit (Ht) level has been reported to be a correlating factor of hypertension in aged people, but has not been examined in younger generation. To investigate the association between Ht and blood pressure (BP) in healthy young workers, statistical analysis was performed for 646 male employees, using cross-sectional health-check data. Ht was positively correlated with systolic blood pressure (SBP) and with diastolic blood pressure (DBP) by Pearson's simple correlation analysis. Multiple regression analysis for SBP and DBP was conducted by stepwise procedure, using Ht, age, body mass index (BMI), and drinking and smoking habits as independent variables. It was revealed that Ht was a significant independent variable for DBP (p < 0.001), as well as age and BMI, but not for SBP. These findings suggest that increased Ht is an important variable for assessing risk for cardiovascular disorders, especially diastolic hypertension, in young male office workers.

Long commuting time, extensive overtime, and sympathodominant state assessed in terms of short-term heart rate variability among male white-collar workers in the Tokyo megalopolis.

To investigate the possible effects of long commuting time and extensive overtime on daytime cardiac autonomic activity, the short-term heart rate variability (HRV) both at supine rest and at standing rest of 223 male white-collar workers in the Tokyo Megalopolis was examined. Workers with a one-way commute of 90 min or more exhibited decreased vagal activity at supine rest and increased sympathetic activity regardless of posture, and those doing overtime of 60 h/month or more exhibited decreased vagal activity and increased sympathetic activity at standing rest. These findings suggest that chronic stress or fatigue resulting from long commuting time or extensive overtime caused these individuals to be in a sympathodominant state. Although these shifts in autonomic activities are not direct indicators of disease, it can be hypothesized that they can induce cardiovascular abnormalities or dysfunctions related to the onset of heart disease. Assessment of the daily and weekly variations in HRV as a function of daily life activities (such as working, commuting, sleeping, and exercising) among workers in Asia-Pacific urban areas might be one way of studying the possible effects of long commuting time, and extensive overtime, on health.

Self-reported sleep quality, job stress, and daytime autonomic activities assessed in terms of short-term heart rate variability among male white-collar workers.

To investigate the relationships among the amount of job stressors, self-reported sleep quality, and daytime autonomic activities, a questionnaire survey was conducted for 223 healthy male white-collar workers, and their short-term heart rate variability (HRV) was also examined. Half of the subjects complained of nightly poor sleep quality. Self-reported poor sleep quality was associated with a qualitative aspect of job stressors characterized by high amounts of "job difficulty", less amounts of "achievement in job", and less amounts of "support by colleagues", and also with high amounts of personal distress and difficulty in changing their mood. Those who complained of poor sleep quality exhibited sympathetic predominance and reduced heartbeat intervals at standing rest, although job stressors was not correlated to HRV. These results suggest that their job stress disrupts nightly sleep, and also that their insufficient sleep at night causes daytime sympathetic predominance. However, the amount of job stressors was not directly associated with HRV. Further studies should focus on the relationships among chronic job stress, the satisfaction of sleep demands, and the daily and long-term variation in cardiac autonomic activities.

Effects of obesity, current smoking status, and alcohol consumption on heart rate variability in male white-collar workers.

In order to examine the effects of mild to moderate obesity, moderate to heavy smoking, and moderate alcohol consumption on cardiac parasympathetic activities and systemic sympathetic activities, a cross-sectional survey was carried out in 282 healthy Japanese male white-collar workers. Their autonomic activities were assessed as amplitudes of spectral components of heart rate variability (HRV) which was measured in the annual physical examination at their work sites. Taking the effects of aging on HRV into account, the cardiac parasympathetic activity at supine rest and its response to a change in posture were reduced in mildly to moderately obese subjects with a body mass index of 21-36, whereas the sympathetic activity was not. The effects of smoking and alcohol consumption on HRV were not confirmed. The above results means that we should consider obesity as a covariate when we examine possible relationships between cardiac parasympathetic activity and other environmental factors. There is a need for further studies on the relationships among obesity, change in parasympathetic activity, and development of health problems. The dose-effect relationships between long-term smoking or alcohol consumption and chronic changes in autonomic activities also remain to be determined.

Specific alteration of the form of selenium in fetal liver on maternal methylmercury treatment.

We have recently reported that maternal administration of methylmercury caused a striking increase in the selenium concentration in fetal liver accompanied by a decrease in selenium-dependent glutathione peroxidase (GSH-Px) activity. These changes resulted in the lowered bioavailability of selenium as far as the GSH-Px activity was concerned. The present study demonstrated that maternal administration of methylmercury caused a specific alteration of the form of selenium in fetal liver. Sephadex G-200 gel filtration of liver cytosols revealed an additional major peak of selenium in the fetal livers of mice treated with methylmercury. This peak was not present in the liver, kidney, or placenta of mothers treated with methylmercury.

Effect of maternal selenium deficiency on the teratogenicity of methylmercury.

The teratogenicity of methylmercury was examined in selenium-deficient and selenium-sufficient mice of the ICR strain. A single oral dose of 75 mumol/kg of methylmercuric chloride (MMC) on day 10, 11 or 12 of gestation caused similar incidences of a cleft palate in the selenium-deficient and selenium-sufficient mice. The treatment on day 11 led to the highest incidence of a cleft palate in both groups. These results suggest that a maternal selenium deficiency has no effect on the incidence or on the critical gestational period for an MMC-induced cleft palate.

Maternal selenium deficiency enhances the fetolethal toxicity of methyl mercury.

The effect of maternal selenium deficiency on methyl mercury fetotoxicity was examined in the ICR strain of mice. Pregnant mice were fed either selenium-deficient diets based on torula yeast or selenium-supplemented diets which were identical to the former except that 0.1, 0.2, or 0.4 mg of selenium per kilogram of diet was added as sodium selenite. Fetolethality of methyl mercury was exacerbated by maternal selenium deficiency when mothers were administered sc 15, 25, or 35 mumol/kg/day of methylmercuric chloride (MMC) on the 13, 14, and 15th days of pregnancy. One-tenth part per million of selenium in the diet was sufficient to protect the fetuses against MMC fetolethality when dams were administered 25 mumol/kg/day of MMC. Mercury concentrations in maternal and fetal tissues were independent of the dietary selenium level. Selenium concentration and glutathione peroxidase (GSH-Px) activity in maternal tissues were unaffected by MMC administration. In fetal liver, on the other hand, selenium concentration was increased and GSH-Px activity was decreased concurrently by maternal MMC administration in the selenium-supplemented groups. Therefore, as far as GSH-Px activity was concerned, the bioavailability of selenium was markedly decreased in fetal liver by maternal injection of MMC. The increase in selenium content in fetal liver, which was observed only in the selenium-supplemented groups, may play an important role in protection against fetolethal toxicity of MMC.