Even people with slightly high blood pressure are twice as prone to cerebral and cardiac vascular diseases, including strokes and heart failures, as those with normal blood pressure, a Japanese study has found.

The higher the blood pressure, the higher the risk of such diseases, a Yokohama City University research team said in an announcement of its research results last month.

"It is necessary to address the risk of disease development from the stage of slightly high blood pressure," said team member Keisuke Kuwahara, associate professor at the university.

The team surveyed 81,876 people aged 20 to 64 who had regular checkups at their workplaces in fiscal 2010 or fiscal 2011 and were not receiving treatment for hypertension at the time. It conducted follow-up surveys for up to nine years to see the relationship between blood pressure and disease development.

During the survey period, 334 people developed a cerebral or cardiac vascular disease.

Of them, 55 were in the so-called high normal blood pressure group whose systolic blood pressure reading, known as the top number, is 120-129 millimeters of mercury (mmHg) and diastolic blood pressure reading, or the bottom number, is lower than 80 mmHg.

Those in the group had 1.98 times the risk of developing cerebral and cardiac vascular diseases when compared with their counterparts in the normal blood pressure group with a first number below 120 mmHg and a second number below 80 mmHg.

The risk was 2.10 times higher in the elevated blood pressure group with readings of 130-139 mmHg and 80-89 mmHg, and 3.48-7.81 times in the stage 1 to 3 hypertension groups with readings of 140 mmHg and 90 mmHg or even higher.

According to the Japanese Society of Hypertension, the country has an estimated 43 million hypertension patients. The condition, if untreated, causes arteriosclerosis to progress, increasing the risk of strokes and heart and kidney diseases.