ORIGINAL CONTRIBUTION Physical Activity and its Relationship to Cardiovascular Risk Factors in Rural Japanese Men

Methods of quantifying physical activity in a population-based sample are needed to examine the relation of physical activity to cardiovascular diseases. We examined validity and reproducibility of an interviewer-administered physical activity questionnaire for men aged 40-59 years in a rural Japanese population. Validity was tested by comparing the estimate of physical activity from a 24-hour diary and maximum oxygen uptake from ergometer exercise test for forty-five men. There was no difference in the estimates of energy expenditure between the questionnaire and the 24-hour diary in each job classfication. Significant correlations were obtained between total activity estimated by the questionnaire and the 24-hour diary (r=0.66) and between the total activity and maximum oxygen uptake (r=0.30). Correlation coefficients between the test and retest at 1-2 year interval for 83 men were 0.67 for total activity, 0.62 for activity at work, 0.59 for leisure time activity and 0.24 for other activity. Using this questionnaire, energy expenditure in total physical activity was measured in 539 men aged 40-59 years living in a rural community of Akita, northeast Japan. Greater physical activity was associated with higher serum HDL-cholesterol levels, lower relative weight index. There was no significant association of physical activity with blood pressure levels, serum total cholesterol, cigarette smoking, and alcohol intake. Thus, greater physical activity was not always associated with lower coronary risk factors except for HDL-cholesterol. Prospective studies will be needed to clarify the relation of physical activity with cardiovascular disease in Japanese. J Epidemiol, 1992; 2 : 97-104.

Epidemiologic studies from the U.S. and European countries have provided evidence that higher physical activity, in particular, leisure time physical activity was associated with lower incidence and mortality of coronary heart disease1-4). One of the major public health recommendations for sedentary Caucasians is an increase of physical activity5). The situations may be different in Japanese because incidence and mortality from coronary heart disease was much lower in Japanese than in Caucasians6-8). Stroke incidence and mortality was higher in Japanese than in Caucasians9, 10). Relation between physical activity and stroke is not consistent. A prospective study of . Relative metabolic rate was assigned 2.5 for farming work in average, 3.5 for non-farming manual work, 0.5 for clerical work, and 1. 5 for other non-farming light work. Non-farming manual work was defined when men reported to be involved in carrying or lifting heavy stuff, handling a heavy cart, and/or using shovel and hammer. Nonfarming light work was defined as work at standing and/or driving a truck, other construction automobiles, and an ordinary car. Clerical work was defined as work at seat (see appendix).
To validate the physical activity questionnaire, 24hour diary of physical activity and ergometer exercise test was conducted for the subsample of 45 men. 24-hour diary of physical activity was determined by the modified method of Bouchard22). The kind of major physical activity in every 15 minutes was recorded. If there was strong but short physical activity, such activity and duration time were also recorded. Energy expenditure during the 24 hours was calculated from the same formula used for the physical activity questionnaire.
Relative metabolic rate for each physical activity was adopted from the reported data from Labor Science institute23). A collaborative study of physical activity among various geographic and occupational populations showed that the 24-hour diary method is feasible and provide a good estimate of physical activity for middle-aged Japanese men 24,25). Ergometer exercise test was done by a stepwise method within 85% of maximum pulse rates, and maximum oxygen uptake was estimated by the Astrand and Ryhming method26). Maximum oxygen uptake was reported to reflect usual physical activity27). Mean values of caloric expenditure from those two different methods and maximum oxygen uptake were calculated according to job classification : farmers , manual workers and clerical workers. Furthermore, correlations among these three variables were calculated.
Reproducibility of the physical activity questionnaire was examined by retesting 83 subsample one to three years apart. Mean energy expenditure was compared in each of classified jobs. Correlations between the two variables were also calculated .
The relation of physical activity with cardiovascular risk factors such as blood pressures, serum total cholesterol, HDL-cholesterol, alcohol intake and cigarette smoking was examined by computing mean values of cardiovascular risk factors according to the quartile of total energy expenditure.
Tests of significance were conducted using analysis of variance. To test whether blood pressures and HDL-cholesterol varies by physi-cal activity after controlling for age and other covariates, the analysis of covariance was used. Then, multivariate-adjusted mean values of blood pressures and HDL-cholesterol were estimated according to the quartile of total energy expenditure. Changes of HDL cholesterol levels associated with a 10 kcal/kg/ weight increase of total energy expenditure was also estimated using a multiple linear regression adjusting for age, relative weight index, alcohol intake and cigarette smoking. All p-values for statistical significance were two-tailed.

RESULTS
Validation of physical activity questionnaire Table 1 shows mean values of energy expenditures estimated by the questionnaire and 24-hour diary, and mean values of maximum oxygen uptake by job. Energy expenditure was calculated for work, leisure time activity and other living activity, separately. Other living activity was defined as activity other than work or leisure time activity, such as eating, washing, bathing, watching TV and sleeping. According to both the questionnaire and 24-hour diary methods, mean energy expenditure at work and total energy expenditure were highest for farmer, intermediate for manual workers and lowest for clerical workers. The same was true for maximum oxygen uptake. There was, however, no difference in energy expenditure for leisure time physical activity and other living activity among the jobs. For each job, there was no difference in mean values of total energy expenditure, and energy     fold thickness was lower in the upper two quatiles than in the lower two quartiles. Mean serum total cholesterol did not vary among the quartiles. Mean HDLcholesterol was lowest in the lowest quartile and progressively higher in the following two quartiles, and the increasing trend was saturated in the highest quartile. Mean alcohol intake was lower in the lower two quartiles and higher in the upper two quartiles although the difference was not significant.
Mean number of cigarettes smoked and the prevalence of current smokers did not vary significantly among the quartiles.
Mean values of systolic and diastolic blood pressures according to the quartile of total energy expenditure were examined after controlling for age, relative weight index and alcohol intake. Adjusted mean values from the lowest to highest quartiles of physical activity were 131 mmHg, 132 mmHg, 131 mmHg and 134 mmHg for systolic (p=0.47) and 84 mmHg, 83 mmHg, 83 mmHg and 84 mmHg for diastolic (p=0.49).
Although blood pressure levels were slightly higher in the highest quartile of physical activity, the difference was not significant. Figure 1 presents mean values of HDL-cholesterol according to the quartile of total energy expenditute for men after controlling for age, relative weight index, alcohol intake and cigarette smoking.
There was a clear dose-response relationship between physical activity and HDL-cholesterol (p=0.02).
A multiple linear regression analysis indicated that an increase of physical activity for 10 kcal/kg/weight was associated with an increase of 3 mg/dl HDL-cholesterol.

DISCUSSION
The present study showed that a simple questionnaire of usual physical activity was validated for a rural Japanese population where the major industry of farming is rice cultivation.
Good validity was ascertained by comparing the estimate of total physical activity by 24-hour diary, and maximum oxygen uptake by submaximum ergometer exercise test. Good reproducibility was also obtained by a test-retest examination. The estimate of physical activity at work also had good validity and reproducibility. Leisure time physical activity was not correlated with maximum oxygen uptake, probably because this activity consisted of less than 1% of total physical activity. However, the estimate of leisure time physical activity showed good reproducibility.
For Caucasians, leisure time physical activity was correlated well with maximum oxygen uptake, but physical activity at work was not27.28). The discrepancy between Japanese and Caucasians is probably due to a larger composition of physical activity at work and a smaller composition of leisure time physical activity in Japanese than in Caucasians.
There was a U-shaped pattern between physical activity and blood pressures although the difference in blood pressure levels among physical activity quartile was not statistically significant. From epidemiologic studies in the U.S. and European countries, low physical activity was associated with higher blood pressure levels in part due to overweight29,30). However, no studies in the U.S. and European countries reported an association of high physical activity with high blood pressures. Several epidemiologic studies in Japan suggested that a very high physical activity was associated with high blood pressure. Blood pressure levels were higher in rural Japanese than in urban population while physical activity level was higher in rural Japanese than in urban Japanese 24). A study for employees of Japan National Railroad indicated that blood pressure levels were higher in manual workers than in clerical workers31). These ecologic studies24,31), however, did not adjust potential confounding factors such as sodium intake and alcohol consumption, and could not determine the causality between a very high physical activity and high blood pressures. Therefore, effects of very high physical activity on blood pressure levels in Japanese remain to be examined.
Mean relative body index was lower in the third quartile of total energy expenditure, and interestingly, was relatively higher in the highest quartile. Mean skinfold thickness, however, was relatively lower in the highest quartile as well as the third quartile of energy expenditure. Thus, men in the highest quartile of physical activity were assumed to have larger muscle mass rather than obesity compared to men in the lower two quartiles.
No association was observed between physical activity and serum total cholesterol which is consistent with previous studies 32, 33). Serum total cholesterol is supposed to be affected by dietary fat intake such as saturated fatty acids, polyunsaturated fatty acids and cholestero16,31).
HDL-cholesterol was positively associated with physical activity. After controlling for age, relative weight index, alcohol intake, and cigarette smoking, a dose-response between physical activity and HDLcholesterol became more evident. The positive association was reported from many epidemiologic studies in the United States25,36) and European countries32,33), but only from a few studies for urban Japanese employees25,36). However, to our knowledge, no population-based study for rural Japanese reported this association.
Therefore, the present study expanded the consistency of the positive association between HDL-cholesterol and physical activity in different ethnic groups. Experimental studies provided additional evidence on the causality between HDLcholesterol and physical activity. A moderate exercise program increased serum HDL-cholesterol by increasing HDL2 fraction 37,38). Physical activity raises activity of lecithin cholesterol acyltransferase (LCAT) in blood and lipoprotein lipase on endotherial cells of peripheral vascular wall, which transform HDL3 to HDL2 directly or indirectly , and inhibit activity of hepatic triglyceride lipase which transform HDL2 to HDL338, 39) Prospective studies from Caucasian populations showed that higher leisure time physical actively was associated with lower incidence or mortality of coronary heart disease1-4,40) A prospective study in Japans) showed without statistical testing that labor intensity and working hours (but not total energy expenditure) were inversely associated with coronary heart disease, and that risk of stroke was higher in the highest qaurtile of total energy expenditure. Although a higher level of blood pressure in the highest qaurtile of physical activity is not statistically significant in the present study, previous studies of Japanese11,24.31), suggested that very high physical activity increase risk of stroke in Japanese. Further studies will be needed to clarify the relation of physical activity with coronary heart disease and stroke in Japanese.  (2) in Ql) Answer the following questions # How many days per week are you usually engaged in farming ? * days # How many hours per day are you usually engaged in farming ? Exclude lunch time and tea break.
hours and * minutes # How many days per week are you usually engaged in non-farming jobs ? * days # How many hours per day are you usualy engaged in non-farming jobs ? Exclude lunch time and tea break. * hours and * minutes # How many hours per day do you sleep ? * hours and * minutes # What king of work do you do for non-farming job ? Choose one or more.
(1) Carry or lift heavy stuff (2) Handle a heavy cart (3) Use shovel or hammer (4) Drive a truck or other construction automobiles (5) Drive an ordinary car (6) Work at seat (7)