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CLINICAL SCIENCES: Clinically Relevant

Commuting, leisure-time physical activity, and cardiovascular risk factors in China

HU, GANG; PEKKARINEN, HEIKKI; HÄNNINEN, OSMO; YU, ZHIJIE; GUO, ZEYU; TIAN, HUIGUANG

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Medicine and Science in Sports and Exercise: February 2002 - Volume 34 - Issue 2 - p 234-238
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Abstract

There is good evidence that a high level of leisure-time physical activity reduces the risk for cardiovascular diseases (CVD) (3,13,14,18,23). One cohort study has demonstrated that cycling to work is inversely associated with all-cause mortality among Danish (1). Epidemiological research has indicated an inverse relationship between leisure-time physical activity and CVD risk factors (2,7,9,10,16,22). To our knowledge, there are little data reporting the association between commuting physical activity and CVD risk factors. Two studies have shown that cycling or walking to and from work decreases the risk for hypertension (5,20), and an intervention study has shown that commuter cycling improves physical performance (8).

Commuting physical activity among Chinese urban people is very different in comparison with Western populations. China is the largest bicycle-using country in the world. The Chinese urban population usually uses bicycle or walks to and from work, school, and shopping. Very few have private cars. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine suggested that every U.S. adult should accumulate 30 min or more of moderate-intensity physical activity on most, preferably all, days of the week (19). It is not known whether both commuting and leisure-time physical activity reduces CVD risk factors in China or other developing countries. The aim of this study was to clarify the relationship between self-reported commuting and leisure-time physical activity with body mass index (BMI), blood pressure (BP), and prevalence of overweight, hypertension, and cigarette smoking among urban Chinese in Tianjin, China.

METHODS

Subjects.

In 1996, a cross-sectional population survey was conducted in urban areas of Tianjin, China. This survey serves as the baseline for an intervention program that was funded by the World Bank. The aims of this program are to decrease levels of behavioral risk factors for noncommunicable chronic diseases through legislative and environmental changes, using the population approach intervention strategy.

The city of Tianjin has a population of 9.5 million, of whom 4 million people live in the six urban districts. The sample of this study was drawn using a two-stage sampling method. First, 14 communities comprising 400,000 inhabitants were drawn randomly with at least two communities from each of the six urban districts. In the second stage, 4000 individuals aged 15–69 yr were drawn randomly from the local population registers in the sampled communities. The sample was stratified by gender and into five 10-yr age groups (oldest age group, 55–69 yr). The subsample of each sampled community was almost the same size. The response rate was 100%. Informed consent was obtained from all participants and the study was approved by Tianjin Public Health Committee for Protection of Human Subjects. Some information was not available from 24 subjects, and therefore 3976 subjects were analyzed in the present study.

Examination.

The survey included a questionnaire and an anthropometric measurement. The questionnaire, which mainly dealt with health status, health care and service, health behaviors, and health knowledge, was completed by home interview. The participants were invited to attend the health centers in the study communities for determination of height, weight, and BP. The health workers, who were from the Disease Prevention Centers at city and district levels, and from the clinics at the subdistrict level, conducted the survey. All health workers were intensively trained in meeting and practice.

Assessment of physical activity.

Information on occupational, commuting, and leisure-time physical activity was assessed with a questionnaire. The respondents reported their occupational activity in the previous year according to a three-class division: 1) sedentary, physically very easy, sitting office work; 2) intermediate, work, including standing and walking; and 3) active, strenuous work. The subjects were asked, if they walked, bicycled, or used the bus when going to and from work, school, and shopping daily and the duration of the above activity. The duration of commuting was categorized into six groups: 0 min (by bus or no commuting physical activity), on foot ≤ 30 min, by bicycle ≤ 30 min, on foot > 30 min, by bicycle 31–60 min, and by bicycle > 60 min. No commuting physical activity group was defined as those who were unemployed, retired, housewives, and who lived inside or very near the workplace. With regard to leisure-time exercise, respondents were asked “During the past 30 days, did you participate in any physical activity or exercises such as running, dancing, ball sports, Qi Gong, or walking for exercise?” Those who answered yes were then given the opportunity to describe details. The frequency of leisure-time exercise and duration of each time were collected. The frequency was classified into four categories: ≥ 20 times, 10–19 times, 5–9 times, and 1–4 times per month. Daily commuting physical activity or commuting plus leisure-time physical activity were classified into four categories: 1) 0 min, 2) 1–30 min, 3) 31–60 min, and 4) more than 60 min. Daily leisure-time exercise was classified into three categories: 1) 0 min, 2) 1–30 min, and 3) more than 30 min.

Cardiovascular risk factors.

Weight was measured, without shoes and light indoor clothing, to the nearest 0.1-kg by using a beam balance scale. Height was measured to the nearest 0.1 cm by using a stadiometer. Height and weight were measured twice and the mean values of the readings were used for the analysis. BMI was calculated by dividing the subject’s weight (kg) by the square of the height (m). Overweight was defined as BMI ≥ 25. BP was measured from right arm using a standard mercury sphygmomanometer after 5 min of rest with the subject in the sitting position. The fifth phase Korotkoff sound was recorded as the diastolic pressure. Following the WHO MONICA Project methodology, BP was measured twice, and the mean of the two BP measurements was used for the analysis. Hypertension was defined as systolic blood pressure (SBP) ≥ 140 mm Hg and/or diastolic blood pressure (DBP) ≥ 90 mm Hg, or using antihypertension drugs.

Information on smoking habits (never, current) and alcohol consumption (never, current) were assessed using a set of questions in the questionnaire. Years of education were divided into three categories: 1) 0–6 yr, 2) 7–12 yr, and 3) 13 yr or more.

Statistical methods.

The data were analyzed using the SPSS program. With general factorial ANOVA models, the means of BMI, SBP, and DBP for activity groups were compared after adjustment for age, education, smoking, alcohol consumption, BMI (except with BMI as dependent variable), and occupational activity. Logistic regression was investigated on the associations between activity groups and percentages of overweight, hypertension, and smoking (with the reference category: 0 min of activity). For all analyses, a two-tailed P < 0.05 was used to indicate statistical significance.

RESULTS

The descriptive characteristics of the study sample are presented in Table 1. Majority of women (67%) and men (61%) reported no leisure-time exercise. About 29% of men and 24% of women had 1–30 min of leisure-time exercise, and 10% participants reported doing more than 30 min of leisure-time exercise. Only 4% women and 9% men reported going to and from work by bus or no commuting physical activity. Over half the men (51%) and women (55%) obtained 1–30 min of commuting physical activity on foot or by bicycle, 30% of men and 34% of women reported 31–60 min of commuting physical activity, and 11% of male and 7% of female subjects bicycled more than 1 h to and from work.

Table 1
Table 1:
Baseline characteristics of study sample by sex in Tianjin in 1996.

Time spent on commuting, leisure-time, or commuting plus leisure-time physical activity was inversely related to BMI (P < 0.05 for trend) and positively related to SBP (P < 0.05 for trend) among men (Table 2). Duration of commuting physical activity was inversely associated with BMI among women (P < 0.05 for trend). The lowest mean DBP and SBP occurred in women reporting 31–60 min commuting, or commuting plus leisure-time physical activity; the highest mean DBP and SBP were seen in those having more than 60 min of these activities (P < 0.01 for trend).

Table 2
Table 2:
Comparison of the adjusted means (SE) of cardiovascular risk factors by physical activity (min·d−1) of urban men and women aged 15–69 in Tianjin, China.a

After being adjusted for age, education, smoking, alcohol consumption, BMI (except with overweight as dependent variable), and occupational activity, duration of commuting, leisure-time, or combined commuting and leisure-time physical activity in men was inversely associated with prevalence of overweight (Table 3). The lowest prevalence of hypertension was seen in both genders who spent 31–60 min commuting or commuting combined with leisure-time physical activity, and the highest prevalence of hypertension was shown in those who did more than 60 min of the above activity as compared with the reference group (P < 0.01 for trend in men and P < 0.05 for trend in women). Time spent on leisure-time exercise was positively associated with the prevalence of hypertension among men (P < 0.05 for trend). The prevalence of smoking was consistently and inversely related to physical activity among both genders (P < 0.05 for trend), although the commuting physical activity group did not reach statistical significance.

Table 3
Table 3:
Adjusted odds ratios (OR) and 95% confidence intervals (CI) for the association between physical activity (min·d−1) and hypertension, overweight, and smoking in urban men and women aged 15–69.a

DISCUSSION

Randomly selected Chinese subjects were representative samples of the urban populations in Tianjin. The high participation rate makes it possible to draw conclusions on physical activity and its association with CVD risk factors.

In China, the daily activity of going to and from work has traditionally been one of the major forms of physical activity. In urban Tianjin, more than 90% people go to work by bicycle or on foot. The Chinese spent more time on commuting physical activity (mean 30 min) than on leisure-time exercise (only about 10 min) (11). This trend is different from Western populations. In the 1999 Finnish surveys, 47% of female and 30% of male subjects spent more than 15 min in daily walking or bicycling to and from work (6). Because those Chinese may obtain health benefits from their commuting physical activity, the relationship between both commuting and leisure-time physical activity and CVD risk factors was analyzed.

Only a few studies have demonstrated association between commuting physical activity and CVD risk factors. Bovens et al. (2) showed that BMI among men and smoking among both genders had a negative correlation with bicycle transport, and BP had no correlation with bicycle transport among both genders. In a study by Pereira et al. (20), American white men in the highest quartile of leisure activity (include walking or cycling to and from work) had a 34% lower odds of developing hypertension over 6 yr compared with the least active. A Japanese prospective cohort study has shown that walking to work and leisure-time physical activity decreased the risk for hypertension in Japanese men (5). Most cross-sectional studies have indicated an inverse relationship between the level of leisure-time physical activity and BMI (7,9,16) and BP (7,9,10,16,22). Several studies suggest that decreased physical activity or increased sedentary behavior plays an important role in weight gain and development of obesity (4,21).

With respect to BMI and prevalence of overweight among men, our results are consistent with the previous studies. The significant association of physical activity and BMI was more evident in men than in women. Commuting or leisure-time physical activity was significantly and inversely related to BMI among men. In women, only leisure-time physical activity had a significant association with BMI. However, in contrast to the findings from other studies, the present study indicated that commuting or leisure-time physical activity was positively related to SBP, and leisure-time exercise was positively related to hypertension among men. More than 60 min commuting or commuting plus leisure-time physical activity was associated with the highest mean BP and the highest prevalence of hypertension among both genders; 31–60 min of the above activity was associated with the lowest mean BP among women and the lowest prevalence of hypertension among both genders. The present study indicated that 31–60 min of physical activity daily may be beneficial to overweight men and hypertensive people. This trend partly supported the American College of Sport Medicine’s recommendation (19).

It is difficult to explain why more leisure-time exercise among men or more than 1 h of commuting physical activity among both genders may be associated with high mean BP. One possible reason for the positive relation is that those persons who perceive themselves as ill accept a prescribed treatment to increase commuting and leisure-time physical activity. Another explanation can be that prolonged daily commuting may increase the mental load. Urban people with long daily trip to and from work by bicycle in the heavy rush-hour traffic are often highly stressed. Dietary factors may also influence level of BP. It is well known that Tianjin has the highest recorded sodium excretion among the 52 centers in the Intersalt study (12), and consumption of salt is positively associated with BP in this population (24). We found that people with a long commuting time eat more vegetables than those with short commuting time (11). One can speculate that subjects having long commuting times consumed more salt in their food.

It is interesting that the percentage of smoking was lower in all physical activity groups and that the prevalence of smoking showed a higher significant decreasing trend from the lowest to highest activity groups. The present study indicated an inverse association between physical activity and smoking, which supported some earlier studies (2,7,10). Higher prevalence of smoking among men is a main public health problem in China (25). Results of this study can provide useful information for health promotion. For example, a recent study reported that vigorous exercise facilitated short- and longer-term smoking cessation in women (15).

We could draw some conclusions from the data that physical activity may be generally favorably associated with some CVD risk factors, for example, BMI and prevalence of smoking. However, more leisure-time exercise in men or more than 1 h of commuting physical activity in both genders may be associated with high mean BP. The cross-sectional design of the study does not allow us to distinguish the relationship between cause and effect. Further research, i.e., prospective study or randomized trials needs to analyze the change trends and the association between long-lasting commuting physical activity and leisure-time exercise and CVD risk factors in the Chinese urban people.

The subjects aged from 15 to 69 included younger-, middle-, and older-aged Chinese people. Persons who are on treatment for hypertension may be less physically active. Therefore, additional analyses with subsets of the total sample, e.g., people aged 15–39 yr or 40–69 yr, or only people without antihypertension drug, were carried out. Only minor changes in the results were observed. Thus, our results were not biased due to these confounding factors.

The present study has some limitations. We could not include possible confounding factors, such as diet. The previous studies demonstrated that dietary energy and fat are associated with BMI (17). BMI is a determinant of BP and also influences physical activity. Overweight could be in part a result of low physical activity. BMI is used as a confounding variable in our analyses of the association between physical activity and other CVD risk factors.

CONCLUSION

The results of the present study show that 31–60 min daily of commuting physical activity on foot or by bicycle, or commuting combined with leisure-time physical activity, may be associated with low BP among both genders. The present study suggests that doing more commuting or leisure-time exercise is associated with lower mean BMI, lower prevalence of overweight among men, and lower prevalence of smoking among both genders.

The authors thank all the coworkers who contributed to the Tianjin Project.

Address for correspondence: Gang Hu, Ph.D., M.P.H., M.D. Department of Physiology, University of Kuopio, P.O. Box 1627, 70211, Kuopio, Finland; E-mail: [email protected]

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Keywords:

BODY MASS INDEX; BLOOD PRESSURE; OVERWEIGHT; HYPERTENSION; SMOKING; CHINA

© 2002 Lippincott Williams & Wilkins, Inc.