Seven Countries Study in Japan

Background/Questions

The Tanushimaru and Ushibuka study populations in Kyushu represented the Japanese contribution to the multi-national Seven Countries Study (SCS) led by Ancel Keys and colleagues. Noboru Kimura, professor of the Third Department of Internal Medicine at Kurume University, suggested using Tanushimaru, a farming village located in Fukuoka prefecture, and Ushibuka, a fishing village located in Kumamoto prefecture, as farming and fishing contrasts but both low-fat consuming areas in the 1950s and 1960s. The research has continued due to the efforts of Hironori Toshima, Yoshinori Koga, Tsutomu Imaizumi, and Hisashi Adachi.

Method/Design

The Seven Countries of the international study were chosen to represent what was likely to be wide contrasts in the fatty acid composition of diets among traditional rural communities to compare CVD rates and trends and associations within and among them. All men aged 40-59 at entry in each of 14 areas in Seven Countries were surveyed and then reexamined for incidence of events at 5 and 10 years, then followed for mortality to the present. Response rates were high and follow-ups complete, as documented in the major SCS monograph (Keys, et al 1980).

Results

Of comparisons among the Seven Countries populations, Tanushimaru and Ushibuka were the first to demonstrate the strong association of low fat intake, low blood total cholesterol levels, and low myocardial infarction rates among the Japanese, a finding of major and historical importance. The Tanushimaru Study was started in 1958, and Ushibuka in 1960. Initially, the follow-up period was ten years among CVD-free healthy long-term residents. Compared to populations in the other six countries, there was markedly decreased risk of coronary artery disease but increased risk of cerebrovascular disease in Japan. (Only Greece had comparably low rates for coronary artery disease.) Japanese diet appeared to have an ideal balance of saturated, monounsaturated and polyunsaturated fats as well as low fat.

Japanese researchers wanted to investigate how diseases changed with time, and therefore recruited new cross sections of healthy people of Tanushimaru on their 40th birthday, mounting a new study using the methodology of the Seven Countries Studies. During 40 years of the study in Tanushimaru, the average energy intake (thus physical activity) was high in 1958, as a large component of the workforce was in occupations of active labor, but it later tapered to 2,000-2,200 calories and became similar to the national average. However, a powerful trend was seen with carbohydrate intake being replaced by fat and protein. The blood cholesterol level increased with age but the mean value remained below 200 mg/dL.

The rate of coronary artery disease in this region was roughly 1 in 1,000/year, and well below the national average. It was tempting to use the values of the Tanushimaru Study to predict coronary artery disease rates in cities, where the rates of coronary artery disease were rising.

Conclusions/Discussion

The Japanese components of the SCS demonstrated among the lowest rates of coronary disease found, despite smoking and blood pressure levels commensurate with that in Western countries. Many aspects of the frequency and trends of CVD in Japan have incited greater inquiry in regard to very low fat diets, the inverse relation of serum cholesterol to stroke rates, and potential protective factors for coronary disease and some cancers in Japanese diet and culture.

Data from Tanushimaru and Ushibuka and mortality from all the seven countries continues to be gathered at regular intervals and deposited in Italy, Netherlands, and Minnesota centers for ongoing analysis. The Tanushimaru and Ushibuka study, which began 45 years ago as original cohorts of the Seven Countries Studies in Japan, continues to this day to monitor the impact of lifestyle and diet on health. (HB)