The Ohasama study compared three types of data: blood pressure readings self-measured at home (Home BP), blood pressure readings taken at a physician’s office (Office BP), and 24-hour ambulatory blood pressure readings (ABP). The comparison made it possible to discover important facts, most importantly, that Home BP data has a closer association with stroke/cerebral infarction development risk and a higher prognostic predictive ability for cardiovascular deaths and all deaths compared to Office BP. Following is evidence based on insights gained from the Ohasama study.

1. Home blood pressure measurement has a stronger predictive power for cardiovascular mortality

When comparing home blood pressure with office blood pressure by using them as continuous variables in Cox's proportional hazards model, it emerged that the average of multiple (taken more than three times) home systolic blood pressure values (Multiple home) was most strongly related to cardiovascular mortality risk. Furthermore, the results showedd that the average of the first two home blood pressure values (Initial home) is also more strongly related to the mortality risk than the office blood pressure values (Screening).

2. The first proposal of reference values for home blood pressure measurement

In the study, the relative hazard of death was evaluated for each home blood pressure value. The results showed that the hazard ratio for the highest mortality rate due to hypertension was 1.7. Using this result, the home systolic and diastolic blood pressure levels calculated when the hazard ratio becomes 1.7, which are 137 mmHg and 84 mmHg respectively, were defined as reference values. Blood pressure levels higher than these were defined as hypertensive. The scientific paper on this definition influenced the AHA guidelines for blood pressure measurement, the ESH guidelines for blood pressure measurement at home, and the JSH guidelines for the management of hypertension.

3. Home blood pressure measurement is a better predictor of the risk of stroke

A morning home systolic blood pressure of 135 mmHg or higher demonstrably increased the risk of ischaemic stroke. Also, for the office blood pressure, there was a tendency toward increased risk as systolic blood pressure level rises, but it was not significant.

The study influenced how medical and health professionals perceived blood pressure globally.

The world’s first large-scale research project on home blood pressure monitoring that involved Ohasama residents influenced international guidelines established by various organizations. Specifically, the US Joint National Committee (JNC), World Health Organization/The International Society of Hypertension (WHO/ISH), The European Society of Hypertension/The European Society of Cardiology (ESH/ESC), and The Japanese Society of Hypertension (JSH), adopted the hypertension reference values of 135/85mmHg based on Ohasama study findings on home BP and ABP.

The degree of trust in the Ohasama study’s outcome of blood pressure reference values of 135/85mmHg, has strengthened over many years and expanded steadily beyond national boundaries. The Ohasama study findings continuously generated from a small town in the Tohoku region have garnered a high reputation among medical and public health professionals in Japan and across the world.