Generational and Regional Differences in Trends of Mortality from Ischemic Heart Disease in Japan from 1969 to 1992

Akira Okayama1, Hirotsugu Ueshima2, Michael Marmot3, Paul Elliott4, Sohel R. Choudhury2 and Yoshikuni Kita2

1 Department of Hygiene and Preventive Medicine, School of Medicine, Iwate Medical University, Morioka, Japan.
2 Department of Health Science, Shiga University of Medical Science, Otsu, Japan.
3 International Center for Health and Society, University College London, London, United Kingdom.
4 Department of Epidemiology and Public Health, Imperial College School of Medicine, London, United Kingdom.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The authors compared generational and regional trends of premature mortality from ischemic heart disease (IHD) from 1969 to 1992 for persons aged 30–69 years. They selected Tokyo and Osaka prefectures as the most urbanized and compared them with the rest of Japan. The data were divided into two periods: period I (1969–1978, International Classification of Diseases, Eight Revision) and period II (1979–1992, International Classification of Diseases, Ninth Revision). In both populations, IHD mortality decreased for both sexes, but mortality from nonspecific heart disease remained constant in men and decreased in women. In Tokyo and Osaka prefectures, the percentage decline per year in IHD mortality for both sexes was significantly smaller in period II than in period I. However, in the rest of Japan, it did not decrease for either sex. Age-specific analysis showed that the percentage decline per year in period II was smallest for the group aged 30–49 years (men, 0.05%; women, 0.76%) in Tokyo and Osaka prefectures, while it was similar for all age groups in the rest of Japan. For men, the IHD mortality rate in 1991–1992 for those aged 30–49 years was higher in Tokyo and Osaka prefectures (9.4/100,000) than in the rest of Japan (5.4/100,000).

ethnic groups; heart diseases; ischemia; mortality; myocardial ischemia; racial stocks; time factors

Abbreviations: ICD-8, International Classification of Diseases, Eighth Revision; ICD-9, International Classification of Diseases, Ninth Revision; IHD, ischemic heart disease.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In 1985, the Japanese had the lowest mortality from ischemic heart disease (IHD) among industrialized countries, and the rate has been declining since 1970 (1Go, 2Go). Declining trends in IHD mortality in Japan can partially be explained by a reduction in blood pressure (3GoGo–5Go). The prevalence of smoking among men has been higher than in other developed countries but has declined gradually (6Go, 7Go), while the rate among women remains low. However, recent nationwide surveys have shown a rapid increase in serum cholesterol levels among the Japanese; the prevalence of hypercholesterolemia (5.76 mmol/liter) doubled from 1980 to 1990 (6Go, 7Go).

Declining trends in IHD mortality in Japan might reflect differing trends among persons living in urban settings in comparison with the rest of Japan. We previously reported different trends in dietary intake of fats and cholesterol, and serum total cholesterol levels, for rural and urban populations (8Go). We found that serum total cholesterol levels in rural populations were lower than in urban populations in the 1960s; although these levels have been increasing more rapidly than those in urban populations, they remain lower. In addition, serum cholesterol levels are higher in younger generations than in older generations, reflecting different dietary habits, a finding in contrast to observations in the United Kingdom and United States (5Go).

We theorized that changes in IHD mortality differ among generations and between urban and rural populations. In the present study, we compared trends of premature mortality due to IHD among populations in Tokyo and Osaka prefectures, the most urbanized area of Japan, with those in the rest of Japan from 1969 to 1992.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Age- and sex-specific mortality numbers for 5-year age groups, by cause of death (117 rubric lists), in 47 prefectures and major cities were available from the Statistics and Information Department, Ministers Secretariat, Ministry of Japan. Underlying causes of death were coded centrally according to the International Classification of Diseases, Eighth Revision (ICD-8) from 1969 to 1978 and the International Classification of Diseases, Ninth Revision (ICD-9) from 1979 to 1992. IHD mortality was identified by ICD-8 and -9 codes 410–414, nonspecific heart disease mortality by codes 415–429, and heart disease mortality by codes 410–429.

We selected the populations of Osaka prefecture (8.7 million in 1990) and Tokyo prefecture (11.8 million in 1990) as the most urbanized in Japan; in 1990, these prefectures contained 17 percent of the entire population in 1.1 percent of the area of Japan. The rest of Japan (population 100 million in 1990) was considered the reference population. Age- and sex-specific populations for the prefectures (5-year age groups) were available for 1965, 1970, 1975, 1980, 1985, and 1990 from the national census, which has been conducted every 5 years and covers more than 99 percent of the population (9Go).

Age- and sex-specific populations for each year from 1969 to 1990 were calculated by taking a weighted mean of these populations from the national census over 2 consecutive years (9Go). Estimated populations were used for 1991 and 1992 (10Go, 11Go). The average age-specific mortality rate for 2 consecutive years was calculated by dividing the number of deaths that occurred over 2 years by the sum of the populations in the age group. To compare the generational difference clearly, we adopted the 30–69-year age band since nonspecific causes of death tend to be used for the elderly. We calculated age-adjusted mortality rates for the groups aged 30–49, 50–59, and 60–69 years as well as for those persons aged 30–69 years. The standard population of Japan that was used was based on the 1985 national census (9Go). Mortality rates for Tokyo and Osaka prefectures and for the rest of Japan were compared between 1969–1970 and 1977–1978 (period I) and between 1979–1980 and 1991–1992 (period II) to examine changes in the trends of the mortality rates by year. By using the Mantel-Haenszel method, we calculated the age-adjusted mortality ratio and its variance to compare rates between generations and periods.


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Heart disease and IHD mortality trends in Japan
Heart disease mortality per 100,000 per year declined from 102 in 1969–1970 to 79.8 in 1991–1992 among men and from 61.6 to 32.0, respectively, among women. Figure 1 shows trends of age-adjusted (age 30–69 years) and figure 2 shows trends of age-specific heart disease and IHD mortality rates in all of Japan, Tokyo and Osaka prefectures, and the rest of Japan for men and for women. Between 1977–1978 (ICD-8) and 1979–1980 (ICD-9), heart disease mortality per 100,000 per year increased from 87.0 to 94.7 among men and from 45.1 to 45.6 among women, presumably because of changes in the coding procedure (12Go). There was no major coding-related change in the IHD mortality rate for either sex. IHD mortality per 100,000 per year declined steadily from 57.5 in 1969–1970 to 27.2 in 1991–1992 among men and from 25.8 to 8.6, respectively, among women (figure 1). For IHD, there was less of a decline in mortality in Tokyo and Osaka prefectures than in the rest of Japan.



View larger version (28K):
[in this window]
[in a new window]
 
FIGURE 1. Age-adjusted (age 30–69 years) trends of heart disease and ischemic heart disease (IHD) mortality per 100,000 for all of Japan, Tokyo and Osaka prefectures, and the rest of Japan among men (1) and women (2) from 1969–1970 to 1991–1992.

 


View larger version (27K):
[in this window]
[in a new window]
 
FIGURE 2. Log-linear age-specific trends of ischemic heart disease (IHD) mortality (per 100,000 persons aged 30–49, 50–59, and 60–69 years) in all of Japan, Tokyo and Osaka prefectures, and the rest of Japan among men (1) and women (2) from 1969–1970 to 1991–1992.

 
Among men, the difference in heart disease and IHD mortality (i.e., nonspecific heart disease) in Tokyo and Osaka prefectures remained unchanged over time (per 100,000, from 41.2 to 37.4 in period I and from 40.6 to 39.4 in period II). The difference in the rest of Japan also remained unchanged (per 100,000, from 44.4 to 42.5 in period I and from 52.4 to 54.4 in period II), while mortality increased from period I to period II. In contrast to the findings for men, nonspecific heart disease mortality among women decreased rapidly both in Tokyo and Osaka prefectures (per 100,000, from 34.2 to 25.4 in period I and from 27.0 to 19.6 in period II) and the rest of Japan (per 100,000, from 36.3 to 27.4 in period I and from 29.8 to 24.1 in period II).

Age-adjusted heart disease and IHD mortality trends in Tokyo and Osaka prefectures and the rest of Japan
Changes in the age-adjusted (age 30–69 years) mortality rates of heart disease and IHD in Tokyo and Osaka prefectures and the rest of Japan in period I (1969–1978, ICD-8) and period II (1983–1992, ICD-9) are summarized in table 1. For men, the percentage decline per year in age-adjusted IHD mortality in period I in Tokyo and Osaka prefectures (2.46 percent) was similar to that in the rest of Japan (2.74 percent). In contrast, in period II, there was an accelerated decline in IHD mortality in the rest of Japan (3.50 percent), while the decline was smaller in Tokyo and Osaka prefectures (1.65 percent). Nonspecific heart disease mortality per 100,000 in Tokyo and Osaka prefectures decreased slightly from 41.2 to 37.4 in period I and from 40.6 to 39.4 in period II, while the rates for the rest of Japan changed from 44.4 to 42.5 in period I and from 52.4 to 54.4 in period II. The observed increase from 1969–1970 to 1991–1992 in nonspecific heart disease mortality in the rest of Japan was due chiefly to changes in ICD-8 and ICD-9 diagnostic criteria.


View this table:
[in this window]
[in a new window]
 
TABLE 1. Changes in age-adjusted mortality* from heart disease and ischemic heart disease among men and women in urban populations and the rest of Japan, period I (1969–1978) and period II (1979–1992)

 
For women, the per-year percentage declines in IHD mortality in period I were similar in Tokyo and Osaka prefectures (3.81 percent) and the rest of Japan (3.76 percent). As for men, the percentage decline in IHD mortality in Tokyo and Osaka prefectures was lower in period II (2.61 percent), while that in the rest of Japan accelerated (4.17 percent). We found that when the sizes of the populations were considered, the decline in IHD mortality in Japan during the entire study period largely reflected the decline in the rest of Japan rather than in Tokyo and Osaka prefectures. Regarding heart disease, the mortality rate in Tokyo and Osaka prefectures was similar to that in the rest of Japan. Nonspecific heart disease mortality per 100,000 decreased in both period I (from 34.2 to 25.4) and period II (from 27.0 to 19.6) in Tokyo and Osaka prefectures. For the rest of Japan, we found a similar per-100,000 decrease in both period I (from 36.3 to 27.4) and period II (from 29.8 to 24.1).

Generational difference in IHD mortality in Tokyo and Osaka prefectures and the rest of Japan
Changes in IHD mortality in Tokyo and Osaka prefectures and the rest of Japan from 1969 to 1992 for the groups aged 30–49, 50–59, and 60–69 years are shown in figure 2 and table 2. While IHD mortality trends were similar across all age groups in the rest of Japan, the declines among younger age groups were smaller than those among older age groups of men in Tokyo and Osaka prefectures in both period I and period II (p < 0.05). The ratio of the per-year percentage change in period II to that in period I ranged from 0.083 for persons aged 30–49 years to 0.72 for those in the group aged 60–69 years. In the latter group, the decline in IHD mortality was significantly smaller in period II than in period I (p < 0.001). However, in the rest of Japan, the declines were significantly larger in period II than in period I for all age groups of men (p < 0.001). The same phenomenon was observed for women in all age groups in Tokyo and Osaka prefectures. The ratio of the per-year percentage change in period II to that in period I ranged from 0.21 for the group aged 30–49 years to 0.79 for those aged 50–59 years. In the groups aged 60–69 and 50–59 years, the decline in IHD mortality was significantly smaller in period II than in period I (p < 0.001). In the rest of Japan, the declining trends remained similar in the groups aged 30–49 and 50–59 years, and a significant larger decline in period II was observed for the group aged 60–69 years (p < 0.001).


View this table:
[in this window]
[in a new window]
 
TABLE 2. Changes in age-adjusted ischemic heart disease mortality* per year among men and women, by age group, in urban populations and the rest of Japan, period I (1969-1978) and period II (1979-1992)

 

    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
To our knowledge, this is the first study finding generational and regional differences in IHD mortality trends among the Japanese population. It shows that the time trends of IHD mortality were consistent with those of cardiovascular risk factors when the Japanese population was divided into urban areas and the rest of Japan.

Comparability of heart disease and IHD mortality trends
The underlying causes of mortality in Japan were coded by using ICD-8 from 1969 to 1978 and ICD-9 from 1979 onward. The IHD criteria changed little during these periods (2Go). As shown in figure 1, there appeared to be no discontinuity between 1969 and 1978 and after 1979–1992 regarding IHD mortality. However, central coding for heart disease was different from ICD-8 to ICD-9 (12Go). Thus, to avoid systematic bias caused by the coding, we compared changes in heart disease and IHD mortality within two periods by using the same versions of this publication (i.e., 1969–1978 and 1979–1992).

The decline in mortality from specific causes might have been due to changes in diagnostic criteria. Recent advances in medical care in Japan may have changed these criteria; in the past, nonspecific terms such as heart failure rather than myocardial infarction tended to be recorded on death certificates (2Go).

For men, continuous declines in IHD mortality were observed in both populations. Nonspecific heart disease mortality remained unchanged in Tokyo and Osaka prefectures. Although the rate in the rest of Japan increased (per 100,000, from 44.4 in 1969–1970 to 54.4 in 1991–1992), this increase was due mainly to the differences in the diagnostic characteristics between ICD-8 (per-100,000 rate, 42.5 in 1977–1978) and ICD-9 (per-100,000 rate, 52.4 in 1979–1980). Thus, in both populations, the shift from nonspecific causes to specific causes of death was not observed over time for men. For women, the decline in heart disease mortality was much higher than that for IHD, and the shift might have occurred among women (figure 1). Considering the shift from nonspecific heart disease to IHD, the declining trends in IHD mortality observed for women might have been underestimated. However, these trends were similar in Tokyo and Osaka prefectures and the rest of Japan during period I and period II. Thus, it appears that observed differences in IHD trends between Tokyo and Osaka prefectures and the rest of Japan were real for both men and women.

Recently, Baba et al. compared causes of death listed on death certificates with those ascertained by reviewing the medical charts (13Go). Corrected IHD mortality rates were 11 percent higher than the rates obtained by using the original coding, but there was no systematic bias over time in the diagnoses between 1983 and 1990. Although these authors compared limited records in the specific region, this finding may also support the finding that the IHD trends for which underlying causes of deaths were used may be real.

There also may be regional differences in the diagnostic criteria, since large hospitals are located mainly in Tokyo and Osaka prefectures. This fact may cause systematic bias in cause-specific mortality rates. For both sexes, ratios of IHD mortality to heart disease mortality have been higher in Tokyo and Osaka prefectures than the rest of Japan (i.e., a nonspecific diagnostic label for IHD, such as heart failure, tends to be used in the rest of Japan). To compare the trends, we used a mortality ratio of 1977–1978 to 1969–1970 for Tokyo and Osaka prefectures and of 1991–1992 to 1979–1980 for the rest of Japan, instead of comparing the mortality rate directly.

We also compared the trends of IHD mortality between the generations in both populations for both sexes, and we observed a significant difference only in Tokyo and Osaka prefectures. Changes in IHD mortality were clearer for the older than the younger generations. It is unlikely that a shift in the diagnostic criteria occurred for the younger generations in the same population for both sexes. On the contrary, similar declines in IHD mortality were observed in all generations for both sexes in the rest of Japan.

Trends of cardiovascular risk factors in Japan
We reported an increase in cholesterol levels among the Japanese population on the basis of nationwide surveys (5Go). We also reported a regional difference in the trends of serum total cholesterol levels between rural areas and Tokyo and Osaka prefectures (8Go). In these prefectures, serum total cholesterol levels were considerably higher than those in rural populations in the1960s, and there were considerable differences in dietary habits (e.g., the quantity of meat consumed per capita per day was 19.5 g in the rural population and 51.3 g in urban areas (8Go)).

Recently, differences in cholesterol levels between the rural and urban areas have been reduced as food consumption habits in the rural population have been westernized (8Go). However, cholesterol levels are still lower in rural than in urban populations. For example, Keys' dietary factor (14Go) is still lower in the rural than in the urban population, although the difference has narrowed because of an increase in the rural population (figure 3).



View larger version (18K):
[in this window]
[in a new window]
 
FIGURE 3. Changes in the estimated Keys' lipid factor (14Go) in rural areas (population < 20,000) and large cities (population >1 million) of Japan from 1966 to 1985 according to the National Nutrition Survey (adapted from Okayama et al. (8Go)).

 
We also reported westernized dietary habits and higher cholesterol levels in the younger generation (5Go). Thus, persons in Tokyo and Osaka prefectures, especially the younger generation, seem to have been exposed to a higher risk for IHD. Marked declining trends in blood pressure, which also have been observed among the Japanese population since 1965, could partially explain the declining trends in IHD (3Go). Studies on blood pressure trends in Japanese populations have reported a significant decline in blood pressure levels in rural populations (15GoGo–17Go), while no changes have been observed in Tokyo and Osaka prefectures (18Go, 19Go). Thus, the increase in serum cholesterol levels and the decrease in blood pressure levels seem to have occurred predominantly in rural populations. In addition, smoking decreased from 61 percent in 1980 to 58 percent in 1990 for men, while the rate for women remained low.

Generational and regional differences in the IHD mortality trends
In the present study, Tokyo and Osaka prefectures were selected as the most urbanized areas of Japan, with 17 percent of the entire population, and we compared these prefectures with the rest of Japan. Since the rest of Japan includes some large cities with a population of more than 1 million (six to eight cities during the period) and we included these cities in the rest of Japan, the observed difference in the trends might have been diluted.

For men, 1969–1970 age-adjusted IHD mortality was broadly similar between Tokyo and Osaka prefectures and the rest of Japan (figure 1). IHD mortality in Tokyo and Osaka prefectures decreased in relation to the rest of Japan in period I. However, in period II, the decline accelerated in the rest of Japan (p < 0.001), while it slowed in Tokyo and Osaka prefectures. A slowdown in the declining trends was observed especially for younger age groups. For women, essentially similar differences were observed. That is, IHD mortality in Tokyo and Osaka prefectures showed a decrease similar to that in the rest of Japan in period I. However, it slowed in Tokyo and Osaka prefectures in period II, while the decline did not decrease in the rest of Japan. These data show that the recent decline in IHD mortality in Japan is not attributable to a decline in Tokyo and Osaka prefectures but mainly to that in the rest of Japan. Konishi et al. reported that, in a rural population with low cholesterol and high blood pressure, patients who died of acute myocardial infarction had a lower degree of stenosis and higher hyaline degeneration of the coronary artery than did patients in an urban population (20Go). Taking into account the trends of cholesterol and blood pressure levels, these authors concluded that the major risk factor for IHD death in a rural population was high blood pressure (20Go).

In our study, differences in mortality trends were observed among age groups of men in Tokyo and Osaka prefectures. In the youngest age group (30–49 years), the decline in mortality over a 20-year period was much less than that in older age groups. In the rest of Japan, declining trends were observed equally for all age groups. For period I and period II, age-specific IHD mortality showed a lower percentage change in the group aged 40–49 years than in the groups aged 50–59 and 60–69 years (p < 0.001). This difference in the percentage change in IHD mortality among generations could be explained partially by the birth cohort effect. A major portion of the groups aged 30–49 years (–1.05 percent) and 50–59 years (–2.05 percent) in period I became aged 50–59 (–1.33 percent) and 60–69 (–2.08 percent) years in period II (table 2). In Tokyo and Osaka prefectures, although different declining trends were observed among different generations, these trends seem to have remained similar over time for the same birth cohorts. These data also support the conclusion that generational and regional differences in the IHD mortality trends are real.

For women, the time trends of IHD mortality in Tokyo and Osaka prefectures showed changes similar to those for men in Tokyo and Osaka prefectures; that is, the decline was larger in period I than in period II, while declining trends in the rest of Japan did not decrease. A generational difference also was observed in Tokyo and Osaka prefectures; the decline was smallest in the group aged 30–49 years (p < 0.001).

The regional and generational differences in IHD mortality trends are consistent with trends of dietary habits and cholesterol levels (8Go). The regional differences in declining trends of blood pressure also agree with these different mortality trends (15Go). These data indicate that the middle-aged population in Tokyo and Osaka prefectures, especially men, may have a higher risk for IHD death than the population in the rest of Japan. This finding concurs with a report that IHD incidence among workers recently increased in urban areas (21Go). We predict that changes in trends of IHD mortality in Japan initially will be observed in urban populations and may predict the future burden of IHD mortality in Japan. Extensive studies to elucidate the incidence of IHD should be conducted among urban populations.


    ACKNOWLEDGMENTS
 
This study was partially supported by a grant from the Japan Heart Foundation and a grant from the Ministry of Health and Welfare, Japan (11020101).


    NOTES
 
Reprint requests to Dr. Akira Okayama, Department of Hygiene and Preventive Medicine, School of Medicine, Iwate Medical University, Utimaru 19-1, Morioka 020-8505, Japan (e-mail: okayamah{at}iwate-med.ac.jp).


    REFERENCES
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Marmot MG, Smith GD. Why are the Japanese living longer? BMJ 1989;299:1547–51.[ISI][Medline]
  2. Uemura K, Pisa Z. Trends in cardiovascular disease mortality in industrialized countries since 1950. World Health Stat Q 1988;41:155–78.[Medline]
  3. Ueshima H, Tatara K, Asakura S, et al. Declining trends in blood pressure level and the prevalence of hypertension, and changes in related factors in Japan, 1956–1980. J Chronic Dis 1987;40:137–47.[ISI][Medline]
  4. Ueshima H. Changes in dietary habits, cardiovascular risk factors and mortality in Japan. Acta Cardiol 1990;45:311–27.[ISI][Medline]
  5. Okayama A, Ueshima H, Marmot MG, et al. Changes in total serum cholesterol and other risk factors for cardiovascular disease in Japan 1980–1989. Int J Epidemiol 1993;22:1038–47.[Abstract]
  6. Ministry of Health and Welfare. National survey on circulatory disorders, 1980. Tokyo, Japan: Japan Heart Foundation, 1983.
  7. Ministry of Health and Welfare. National survey on circulatory disorders, 1990. Osaka, Japan: Japan Cardiovascular Research Foundation, 1993.
  8. Okayama A, Ueshima H, Marmot MG, et al. Different trends in serum cholesterol levels among rural and urban populations aged 40 to 59 in Japan from 1960 to 1990. J Clin Epidemiol 1995;48:329–37.[ISI][Medline]
  9. Bureau of Statistics, Management and Coordination Agency. National census, 1965, 1970, 1975, 1980, 1985 and 1990. Tokyo, Japan: Japan Association of Statistics, 1967–1992.
  10. Population estimates as of October 1, 1991. Population estimates series. Vol 63. Tokyo, Japan: Statistics Bureau,1992:54–9.
  11. Population estimates as of October 1, 1992. Population estimates series. Vol 65. Tokyo, Japan: Statistics Bureau, 1993:56–61.
  12. Statistics and Information Department, Minister's Secretariat, Ministry of Health and Welfare. Vital statistics. Tokyo, Japan: Ministry of Health and Welfare, 1981.
  13. Baba S, Ozawa H, Sakai Y, et al. Heart disease death in a Japanese urban area evaluated by clinical and police record. Circulation 1994;89:109–15.[Abstract]
  14. Keys A, Anderson JT, Grande F. Serum cholesterol response to changes in the diet. IV. Particular saturated fatty acids in the diet. Metabolism 1965;14:776–87.
  15. Shimamoto T, Komachi Y, Inada H, et al. Trends for coronary heart disease and stroke and their risk factors in Japan. Circulation 1989;79:503–15.[Abstract]
  16. Isomura K, Masuo I. Studies of recent trends in nutritional status and risk factors for cardiovascular disease in a farming village, Nagano. (In Japanese). J Jpn Assoc Cerebro-Cardiovasc Dis Control 1987;22:119–25.
  17. Huse H, Yamamoto K, Ida H, et al. Trends in risk factors for cardiovascular disease in Aito town over the past ten years. (In Japanese). Jpn J Public Health 1991;38(suppl):369.
  18. Konishi M, Iida M, Naito Y, et al. A study on the changes of risk factors for cardio- and cerebro-vascular diseases among a working population in a city. Jpn J Public Health 1987;34:11–22.
  19. Okayama A, Ueshima H, Chiba N, et al. Trends in risk factors for cardiovascular disease in a working population. (In Japanese). Sangyo-Igaku 1991;33:823.
  20. Konishi M., Komachi Y, Iso H, et al. Secular trends in atherosclerosis of coronary arteries and basal cerebral arteries in Japan: Akita pathology study. Arteriosclerosis 1990;10:535–40.[Abstract]
  21. Okayama A, Funakoshi T, Akehi A, et al. Changes in long-term absence due to cardiovascular disease among middle-aged workers in a factory of Japan. Bristol, United Kingdom: Taylor & Francis Ltd, 1995.
Received for publication April 26, 1999. Accepted for publication October 10, 2000.