A U-shaped association between home systolic blood pressure and four-year mortality in community-dwelling older men.

BACKGROUND

Several studies in older people have found a U-shaped or J-shaped association of blood pressure with mortality. The increased mortality associated with the lowest levels of blood pressure in older people have been explained by concurrent illnesses and frailty, but previous studies used blood pressure measured on a single occasion. Such a casual value is different from the long-term average of blood pressure. We investigated the relation between the average level of 5-day consecutive home blood pressure and mortality in older people while adjusting for potential confounding factors including morbidity and frailty at baseline.

METHODS

In 1992, 1186 community residents of a rural Japanese town, Kahoku, aged 65 or older, measured their blood pressure in their homes 20 times (four times per day, 5 consecutive days). The mean value of the 20 measurements was used to examine the association between home BP and subsequent 4-year mortality. A proportional hazards model was fitted while adjusting for activities of daily living impairment, medical history, antihypertensive medication, smoking, use of alcohol, and depression.

RESULTS

A total of 134 persons died during the four-year follow-up period. There was no significant evidence that frailty is more prevalent in the lowest or highest systolic BP group than in intermediate groups. A U-shaped association between the average level of home systolic blood pressure and mortality was found in men while adjusting for potential confounding factors, including morbidity and frailty. We also showed the U-shaped curve of the association of systolic BP with all cause and noncardiovascular mortality in the whole population and the linear association of systolic BP with cardiovascular mortality.

CONCLUSIONS

We showed a U-shaped association between the average level of systolic blood pressure measured at home and mortality in older men while adjusting for potential confounding factors including morbidity and frailty. Not only high home systolic BP, but also low home systolic BP, is an independent risk factor for mortality in older men. The mechanisms underlying the association between BP and mortality differ by levels of systolic BP. Cardiovascular deaths tended to be higher in the highest SBP group, and only noncardiovascular deaths were increased in the lowest SBP group. The latter finding suggests that low SBP may be not only an independent risk of mortality but also an indicator of a subclinical noncardiovascular comorbid condition.