Long Commuting Time, Extensive Overtime, and

Industrial Health 1998, 36, 209-217

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

Takayuki KAGEYAMAI*, Noriko NISHIKIDO2, Toshio KOBAYASHI3,

Yoshika KUROKAWA4, Tetsuya KANEKO$ and Michinori KABUTO4

' Department of Mental Health and Psychiatric Nursing , Oita University of Nursing and Health Sciences, 2944-9

Megusuno, Notsuharu, Oita 870-1201, Japan 2 Department of Community Health Nursing , St. Luke's College of Nursing, 10-1 Akashicho, Koto-ku, Tokyo

104-0044, Japan 3 Health Science Center , Tokyo University of Mercantile Marine, 2-1-6 Etchujima, Koto-ku, Tokyo 135-0044, Japan 4Regional Environment Division , National Institute for Environmental Studies; 16-2 Onogawa, Tsukuba, Ibaraki

305-0053, Japan 5 Department of Environmental Health , Faculty of Health Sciences, Kyorin University, Miyashita-cho 476, Hachiohji, Tokyo 192-0005, Japan

Received November 25, 1997 and accepted February 3, 1998

Abstract: 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.

Key words: Commuting time, Overtime, Heart rate variability, Sympathodominant state, Chronic stress,

Cardiovascular dysfunction

*To whom correspondence should be addressed.

210

Introduction

According to an article in a Japanese newspaper, nutritional

researchers recently found that the rapid urbanization and industrialization in Asia-Pacific countries have resulted in

long commuting times and extensive overtime, and

consequently sleep deprivation and the skipping of breakfast for workers in urban areas in these countries'. The Tokyo

Megalopolis is comprised of central Tokyo and densely

populated areas within 50-100 km of central Tokyo2~. The number of people who commute from municipalities located within 30-70 km of central Tokyo to central Tokyo by public

transport has increased3~. This commute often exceeds 90 min one-way, and the public transport is generally very

crowded3~. However, only a few reports on the effects of commuting on health are available4~. Walking and cycling as

a part of regular commute can contribute to enhancement of cardiovascular function5~ and a decrease in cardiac mortality6~, while a commute by car or public transport is a possible

stressor4~ being related to various subjective symptoms7~, absenteeism due to sickness7~, and a high preterm birth rate8~.

It seems reasonable to suggest that an excessive workload

is harmful; e.g., the socio-medical Japanese term "karoshi" is used in Japan to refer to fatal heart attacks triggered by a heavy workload9~. In many cases of workers who suffered

fatal heart attacks and for whom workers' compensation was claimed, the amount of their overtime or holiday work before

the attack was extensive9j. Although neurogenic and hormonal factors are suggested to be involved in the development of heart disease, little hard evidence that physical or psychological

overwork can increase mortality or morbidity is available'° Although daily overtime and difficulty in taking days off have

also been suggested to increase the risk of malignant essential hypertension'1) and cerebral hemorrhage12~, the underlying mechanisms have not been identified.

Spectral analysis of heart rate variability (HRV) noninvasively provides specific indices related to cardiac

vagal activity and systemic sympathetic activity'3-'6~. These indices indicate the severity of heart disease17'18) and can

also be used to predict the risk of sudden death19,20), cardiac

death21,22}, and occurrence of arrythmic events19-21} in heart

disease patients. They also indicate the early phase of the borderline- and mild hypertension2S~, the level of

environmental stress in asymptomatic 2324 26) and

predict mortality in the general population27~. If a long commuting time or overwork is associated with the shift in autonomic activity assessed in terms of HRV, this shift might

induce, or might indicate the presence of, cardiovascular

T KAGEYAMA et al.

abnormalities or dysfunction related to the above health

problems25, 26). In order to investigate these possible associations, short-term HRV among male white-collar

workers in the Tokyo Megalopolis was examined in the

present study (a summary of this study also has been reported briefly elsewhere28~).

Subjects and Methods

The subjects were 223 male Japanese white-collar workers

working at a private company located in the Tokyo Megalopolis, who have also participated in another study29~. When they underwent an annual physical examination at

their work sites on Tuesday, Wednesday, or Friday, they were asked to participate in this study in addition to undergoing

the routine checkup. Those who were under some form of medical care, those who had taken any kind of drug on the

day of the examination, and those who had taken a meal or beverage in the 2 h before the examination were excluded

from the study. Information about their daily habits was obtained via a self-administered questionnaire and confirmed through interviews with public health nurses. Their mean + SD age was 30.8 + 5.4 yr (range 21 to 42 yr), and their mean ± SD body mass index (BMI, kg/m2) was 23.3 ± 3.6

(range 16.3 to 36.8). Seventy-one percent were system engineers and 64% were married. The method used to assess HRV is described in detail

elsewhere29~. After they underwent the routine checkup in

the late morning or early afternoon, they lay quietly on a bed for a few minutes. An electrocardiogram (ECG, standard lead II) was recorded for each at supine rest for 3 min. Then,

they stood up unaided, and an ECG was recorded at standing rest from 1 min after the change in posture to 3 min after

the change in posture. The subjects were instructed to breathe regularly and not deeply during the ECG recording. Although

5-min ECG recordings are preferred for the analysis of short-term HRV30~, there was insufficient time to do this because

this study was carried out as a part of the routine physical examination; a 2-min recording is, however, the minimum

amount of recording time for the following analysis of short-term HRV30>

Autoregressive spectral analysis and component wave

analysis'6, 29) were applied to the heartbeat intervals determined from the ECGs for extraction of the high-

frequency component with a center frequency (VHF, Hz) of 0.15-0.30 Hz resulting from respiratory sinus arrhythmia

(RSA) and the low frequency component with a center frequency (ELF, Hz) of 0.05-0.15 Hz resulting from Mayer


COMMUTING TIME, OVERTIME, AND SYMPATHDOMINANT STATE 211

wave-related sinus arrhythmia (MWSA). The power densities of these components (HF and LF, msec2) were calculated. For the purpose of excluding the effects of breathing frequency on HF, coefficients of variation for HF and LF (C-CVHF and C-CVLF, o) were also calculated, according to the following equation: C-CVk =100*Pk12/RR, where k=RSA or MWSA, Pk=power density of k component

(msec2), and RR=mean R-R interval (msec)16-'g, 29~. Then, C-CVHF was standardized for breathing frequency (=fHF)' according to the previously described methods3l, 32~. The HF or C-CVHF mainly indicates cardiac vagal activity, while the LF is correlated both to sympathetic activity and vagal activity13-16~. The C-CVLF/C-CVHF mainly indicates systemic sympathetic activity or sympathovagal balance'4,15,33)• One-way commuting times were classified into three groups

(short, <60 min; moderate, 60-89 min; long, >=90 min), according to the methods described in previous reports3' g). The standard workweek of the subjects was 40 h. The amounts of overtime they had worked in the last three months were classified into three groups (standard, <20 h/mo; large, 20-59 h/mo; very large, >=60 h/mo). The methods for classifying current smoking status and current alcohol consumption of the subjects, and measurement of their height and weight are described elsewhere29~. Covariate analysis was carried out using the General Linear Model (GLM) procedure of SAS34~ to determine whether HRV parameters (HF, C-CVHF, LF, and C-CVjC-CVHF both at supine rest and at standing rest) are associated with commuting time and amount of overtime. HF and LF were, however, logarithmically converted because in this analysis the normality of dependent variables is required. Age was assumed as a covariate, and BMI was classified by its quartiles among the subjects (group 1, BMI<20.6; group 2, 20.6 s BMI<22.3; group 3, 22.3 s BMI<25.2; group 4, 25.2 s BMI).

Results

Most of the subjects were commuting by public

transportation (train and/or bus). A weak inverse correlation was observed between commuting time and amount of

overtime (Table 1). Amount of overtime was positively correlated with the number of holidays (including Saturdays)

worked per month (Table 2). There was no difference in age or BMI among commuting

time groups or overtime groups. As shown in Table 3, the long

commuting time group showed decreased C-CVHF at supine rest and increased C-CVLF/C-CVHF regardless of posture. The

very large amount of overtime group showed decreased HF and increased C-CVLF/C-CVHF at standing rest. These associations were confirmed by the GLM analyses (Table 4)

taking the possible covariates of HRV parameters (age, BMI, current smoking status, and current alcohol consumption) into account. However, heart rate was not correlated with commuting

time or amount of overtime regardless of posture. The relationships between commuting time, and overtime,

and the amount of time spent sleeping are shown in Table 5.

The amount of overtime was positively correlated with the amount of time spent sleeping on nights before holidays

(p<0.05). Commuting time was negatively correlated with the amount of time spent sleeping on weekdays (p<0.05).

However, neither the amount of time spent sleeping on weekdays nor that on nights before holidays was correlated with any of the HRV parameters. As a result, the amount of

time spent sleeping could not explain the associations of HRV

parameters with amount of overtime and commuting time. As shown in Table 6, the frequency of taking exercise

was not correlated with commuting time or overtime. The frequency of taking exercise also showed no correlation with

HRV parameters.

Table 1. Distribution of commuting time and overtime

212 T KAGEYAMA et al.

Table 2. Amount of overtime and number of holidays worked

Table 3. Mean (SD) of HRV parameters

Table 4. Results of covariate analysis of heart rate variability parameters


COMMUTING TIME, OVERTIME, AND SYMPATHDOMINANT STATE

Table 5. Amount of sleep as a function of amount of overtime or commuting time

213

Table 6. Frequency of taking exercise by amount of overtime or commuting time

214

Discussion

The long commuting times of the subjects are common

among workers in the Tokyo Megalopolis2' 3), although such lengthy commutes are rare in western countries4). The

overtime worked by the subjects is not particularly long for Japanese workers9' 11), probably because this study was

performed when economic business conditions in Japan were poor. The associations of age and BMI with HRV parameters agree with the results of previous studies, as discussed

elsewhere29). On the other hand, current smoking status or current alcohol consumption is not correlated with HRV

parameters. This may reflect the fact that few heavy smokers and heavy drinkers are included in the present study, as

mentioned elsewhere29).

As shown in Table 3 and 4, C-CVHF at supine rest among the long commuting time group was significantly decreased,

and their C-CVHF at standing rest as well as HF regardless of posture exhibited similar tendency to it. HF at standing rest among the subjects doing the very large amount of

overwork was significantly decreased, and their HF at supine rest as well as C-CVHF regardless of posture exhibited similar

tendency to it. These results show their reduced vagal activities. On the other hand, the increase in C-CVLF/C- CVHF among these subjects show their sympathetic

hyperactivities. The fact that no increase in LF was observed among them suggests that the increase in LF was canceled by the above decrease in vagal activity, because LF is

correlated not only to sympathetic activity but also to vagal activity15,,6,18, 31, 33) In short, it was suggested that both long commuting time and extensive overtime were independently

associated with a sympathodominant state assessed in terms of short-term HRV. Although the reason of these associations

were not directly examined in this study, we would like to discuss some possibilities.

The above results are unlikely to be biased by the physical exercise undertaken by the subjects during their working

hours. Although physical exercise acutely induce sympathetic

predominance assessed in terms of HRV and this aftereffect is observed even 24 h after the exercise is completed35, 36),

our subjects were white-collar workers who rarely exercised strenuously during their work. They spent 15-20 min in a

routine chekup and then lay quietly for a few minutes on a

bed before the HRV measurements. It also seems unlikely that the sympathetic hyperactivity of our subjects due to

long commuting time remained for hours after they arrived at their offices, because the relative metabolic ratio for the

commute by public transport in the Tokyo Megalopolis is

T KAGEYAMA et al.

only one-third of that for jogging37). The frequency of taking

exercise, which included exercise taken during the noon recess, did not explain the association of the amount of

commuting time or overtime with HRV. Although the effects

of athletic training on HRV have been reported36), it is unlikely that regular commuting by bus or train, as a physical exercise,

affects on cardiovascular functions5). Commuting by crowded public transport, which is often

compared to "hell" in the Tokyo Megalopolis, requires isotonic contraction; commuters often feel local fatigue and

mental fatigue rather than general fatigue37). It is possible that this mental fatigue or psychological stress is associated

with the sympathodominant state in the subjects with a long commuting time; this should be confirmed in further studies.

The sympathodominant state induced by mental arithmetic3S) usually disappears within a few minutes of the

cesation of the task24). Since our subjects spent 15-20 min in a routine checkup and then lay quietly on a bed for a few minutes before the HRV measurements, their mental

workload conducted before the checkup is unlikely to be the cause of their sympathodominant state. It seems, however, reasonable to expect that workers who do a lot of overtime

often feel busy, out of time, hassled, and stressed, even during the daytime. It can be hypothesized that these persistent feelings can be stressors which induce the sympathodominant

state. If this is the case, relaxation training may be effective for reducing sympathetic predominance38). The reason why

extensive overtime was associated only with the sympathetic hyperactivity at standing rest, not with that at supine rest

(Tables 3 and 4), remains unclear. This may be related to the results of a previous study39) which suggested that the

increase in LF of systolic blood pressure power spectrum

after a cognitive task was observed at sitting rest, not at supine rest. Takahashi and Arito39) argued that increased

sympathetic activity after the task may be counteracted by vagal activity associated with supine position, although this interpretation needs to be confirmed in further studies.

The possible aftereffects of sleep on cardiac autonomic

activity should also be discussed. It is suggested that mental workload at night reduces the quality of subsequent sleep'0'41).

It has been shown that sleep deprivation or reduced sleep

quality affect autonomic activity on the following day41-44) In the present study, long commuting time seems to deprive

time spent sleeping on weekdays (Table 5), in agreement with the results of a nationwide social survey45° a6), and workers

doing a very large amount of overtime seem to make efforts to recover from their fatigue on weekdays by sleeping for a

increased number of hours on nights before holidays (Table



5). These correlations were, however, not strong. Thus,

the amount of time spent sleeping could not explain the associations of commuting time or the amount of overtime

with HRV parameters. Since there are large individual

differences in sleep requirements, and the actual amount of time spent sleeping in general does not indicate the

satisfaction of sleep demand, future studies should assess

the satisfaction of sleep demand focusing on the possible effects of sleep deprivation on cardiac autonomic activities in workers.

The sympathodominant state observed in our subjects are

not direct indicators of disease. However, it has been suggested that the chronic sympathodominant state is related

to the onset of cardiovascular disorders26, 47), and also to the early phases of borderline- and mild hypertension2S~. If the sympathodominant state persists for many days, it can,

therefore, be hypothesized that this state can induce, or may indicate the presence of, cardiovascular abnormalities or dysfunctions related to the onset of heart disease or

hypertension25, 26). On the other hand, this sympathetic

predominance also may explain the finding that the workers complaining of unexplained fatigue exhibited an increased

LF at rest48~. In conclusion, our findings lead the hypothesis that chronic

mental strain, fatigue, or sleep deprivation resulting from

long commuting time or extensive overtime causes a sympathodominant state in workers, although the underlying

mechanisms of these relationships remain unclear in this cross-sectional study. This sympathetic predominance itself

is not a direct indicator of disease. However, the hypothesis that this can induce, or indicate the presence of, cardiovascular abnormalities or dysfunctions related to the onset of heart

disease or hypertension should be investigated in future studies. These studies should focus on longitudinal

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. This might be one way of studying the possible

effects of long commuting time and extensive overtime on health.

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Documents

Long Commuting Time, Extensive Overtime, and