Low diastolic blood pressure and mortality in a population-based cohort of 16913 hypertensive patients in North Karelia, Finland

Abstract

Objective: To examine the relationship between mortality and diastolic blood pressure during treatment.

Design: A prospective follow-up of a population-based dynamic cohort of hypertensive patients.

Setting: Province of North Karelia, eastern Finland.

Patients: A cohort of 16 913 North Karelian hypertensive patients in hypertension register of the North Karelia Project, who had been followed up since 1972 until the end of 1985. Most of these patients had been under antihypertensive drug therapy during the follow-up.

Main outcome measures: Death: all deaths (n = 4490), deaths from cardiovascular disease (n = 2995) and deaths from non-cardiovascular disease (n = 1495).

Results: Of all deaths, 17% of those among men and 24% of those among women were of patients with mean diastolic blood pressures less than 90 mmHg. We found a U-shaped relationship between diastolic blood pressure and total, cardiovascular and non-cardiovascular mortalities. We investigated this relationship in more detail using Cox regression model. Low diastolic blood pressure was associated independently with increased mortality for the patients aged 50 years or more at baseline. The occurrence of cardiac failure and other cardiovascular complications of hypertension were more important determinants of mortality than was low diastolic blood pressure alone.

Conclusions: We demonstrated that there is an association between low diastolic blood pressure and mortality for treated hypertensive patients aged 50-69 years. The clinical importance of this relationship for patients without any cardiovascular complications of hypertension seems negligible. For patients with complications, these complications are likely to be primary factors causing greater than normal mortality and low diastolic blood pressure is mostly a secondary phenomenon. Our data do not lend support to speculations that there is overtreatment of hypertension, which would increase mortality through making diastolic blood pressures too low.