Mortality in the JACC Study till 1999

BACKGROUND: We have been conducting a cohort study named “the Japan Collaborative Cohor Study (JACC Study) for Evaluation of Cancer Risk sponsored by the Ministry of Education, Science, Sports and Culture of Japan (Monbusho)” since 1988. The aim of this paper is to describe the mortality of our JACC cohort in the follow-up period from 1988 through 1999, to compare it with the mortality, especially cancer deaths, of the Japanese population in the same period and to compare the causes of mortality by district among the cohort. METHODS: We conducted a follow-up study of 110,792 Japanese inhabitants aged 40-79 years in 1988-1990 for about 10 years to the end of 1999. RESULTS: Of 46,465 males, 37,750 (81.2%) were alive, 7,238 (15.6%) were dead and 1,477 (3.2%) had moved out of the study areas. The figures were 57,016 (88.6%), 4,940 (7.7%) and 2,371 (3.7%) among 64,327 females, respectively. The mean follow-up period was 9.9 years. The proportion of cancer deaths by site in our cohort members was almost same as the Japanese population aged 40-79 years old in 1995. Sex-specific standardized mortality ratios of total deaths, all cancer deaths, and most cancers in our cohort were less than 100 in both males and females for total cohort and the cohort by district. CONCLUSION: Our cohort members appeared to be almost the same or slightly healthier and less likely to die from total causes and cancers than the general population.


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base in the Ministry of Health and Welfare were re-coded in 1999 according to the ICD 10th version (after 1995), using a specifically developed computer program 4 for converting the ICD 9th code to the 10th.
Follow-up condition (alive, dead, or moved) by sex and age group at entry as of the end of 1999 was computed.For those dead, causes of death, especially of cancer deaths, by sex and age group at entry as of the end of 1999 were also computed.Sex-specific standardized mortality ratios (SMRs) were calculated using sex-and age-specific person-years of following-up and sex-and age-specific mortality rates for all Japan in 1988-1999. 5From a practical reason, the mortality rates in 1989 were used for the follow-up data in 1988-1990, and by the same manner, the rates in 1992, 1995, and 1998 were used for each three years of followup.Confidence intervals of SMR were calculated according to chi-square distribution when the observation number was 10 or larger, 6 and according to Poisson distribution when less than 10. 7 Our entire study design, which comprised singular and collective use of epidemiologic data and biological materials (serum only), was approved in 2000 by the Ethical Board at Nagoya University School of Medicine, where the central secretariat of the JACC study is located.

RESULTS
Table 1 shows the age distribution of the cohort members aged 40-79 years at the time of their enrolment in the study and their follow-up condition as of the end of 1999.Of 46,465 males, 37,750 (81.2%) were alive, 7,238 (15.6%) were dead, and 1,477 (3.2%) had moved out of the study areas.The figures were 57,016 (88.6%), 4,940 (7.7%), and 2,371 (3.7%) among 64,327 females, respectively.The mean follow-up period was about 10 years.
Total cancer deaths accounted for 38.7% (2,798) and 35.0% of mortality by district among the cohort.

METHODS
The The follow-up survey was conducted using population registries in local municipalities to determine the vital and residential status of the cohort in each area.All the cases that moved out of the study areas were treated as censored cases.Five subjects who were expunged from their residence record by authorities were also treated as censored cases and included in cases that moved out for computing the cohort numbers by follow up status as of end of 1999.All deaths that occurred in the cohort were ascertained by death certificates from local public health centers in the study areas under the authorities' permission from the Director-General of the Prime Minister's Office (Ministry of Public Management, Home Affairs, Post, and Telecommunications).The underlying causes of death were coded according to the International Classification of Diseases and Injuries (ICD) 10th version by verifying computer-stored data in the Ministry of Health, Labour and Welfare with the permission.Those already coded according to the ICD 9th version (from the time of the baseline survey through 1994) and stored in the computer data-

DISUCUSSION
The follow-up condition of cancer deaths by site as of the end of 1999 was almost same as of the end of 1997. 1 The three commonest sites, cancers of the lung, stomach, and liver in males were of the same order and almost the same proportion among all cancer deaths as of the end of 1997. 1 Among females, the three commonest sites, cancers of the stomach, large intestine, and lung were same in each site as of the end of 1997, 1 but the proportion of cancer of the large intestine (12.3%) exceeded that of the lung (11.8%) if the cancer of the colon and rectum were combined.SMRs of total deaths, all cancer deaths, and most site-specific cancers were less than 100 in both males and females.This means that our cohort members appeared to be less likely to die from total causes and cancers in comparison with the Japanese population as observed other Japanese cohort. 8Because some of the cohort members were selected from participants in health checkups or other kinds of screening, they might have had slightly healthier lifestyles that prevented them from dying with lifestyle related diseases such as cancers and cerebrovascular diseases.Cohort members of each district also appeared to be slightly healthier than the general population, as most SMRs of total deaths and site-specific cancer deaths by district were less than 100.It might be due to the small cohort size that some SMRs of site-specific cancer deaths by district were more than 100.Even though our cohort members were slightly healthier than the general Japanese population in the study period, internal comparisons between an exposed group and a group of unexposed to any factors within the cohort can also be justified as a cohort study.

MEMBER LIST OF THE JACC STUDY GROUP
The present investigators involved, with the co-authorship of this paper, in the JACC Study and their affiliations are as follows: Dr. Akiko Tamakoshi (present chairman of the study group), Nagoya

Table 1 .
Age distribution of cohort members at entry and deaths/move-outs as of the end of 1999.

Table 2 .
Age distribution of total deaths, all cancer deaths, and site-specific cancer deaths as of the end of 1999.

Table 3 .
Sex-specific satandardized mortality raios (SMRs) and 95% confidence intervals (CI) of total deaths, all cancer deaths, and site-specific cancers by district.