Hirosaki University Study

Background/Questions

Naosuke Sasaki and associates from the Department of Hygiene in Hirosaki University, early noticed regional variations in mortality rates from cerebrovascular disease in Japan. Their special interest was the high dietary salt intake of Japan’s Tohoku district. Collaborating in the 1950s with the discoverer of the hypertension-prone rat, pathologist LK Dahl, Sasaki and associates sought to find out if Japan’s northern region, well known for its high salt intake, had higher rates of hypertension and CVD morbidity compared with its lower-salt southern counterparts.

Methods/Design

In an ecological study, Sasaki and associates correlated national data on salt intake, hypertension and cerebrovascular morbidity and determined that the Tohoku district, with high salt intake, had the higher rates of hypertension and cerebrovascular disease. In researching the regional variations in cerebrovascular disease, Sasaki and associates became pioneers in the epidemiological study of cerebrovascular disease, the major killer in Japan. L. Dahl’s presentation of these data in 1960 led to the wide recognition of the relation of dietary salt and hypertension and set the base for Sasaki’s surveillance of blood pressure and diet trends among the people of Nishimemura in Akita Prefecture . From 1954, blood pressure measurements and diet history taken from tens of thousands of people of Akita and Aomori Prefecture were followed for CVD incidence.

Results

In addition to the clear ecologic and individual relations found for diet, blood pressure and disease, they observed that apple growers had lower mean blood pressure and hypothesized that the potassium in apples they ate contributed. To explain the apparent blood pressure lowering properties of apples they undertook an intervention study now underway.

Conclusions/Follow-up

Sasaki and associates’ pioneering ecological study on the association among dietary salt, hypertension, and cerebrovascular disease became widely accepted due to Dahl’s presentations. Following this research, Jeremiah Stamler and Geoffrey Rose and colleagues initiated a multi-national epidemiologic investigation (INTERSALT) to test Dahl’s theories on dietary salt and blood pressure, within and among contrasting populations, using standardized methods. (HB)