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Introduction
In western societies blood pressure rises with age. It is not clear if this is the result of a pathological process that needs treatment or if it is part of the natural ageing process. Treating hypertension helps prevent stroke and coronary heart disease in middle aged and elderly people younger than 80. In two trials, however, no benefit of treatment was observed in subjects aged 80 and older. 1 2 Treating isolated systolic hypertension does not reduce all cause mortality in this age group, although it prevents stroke and heart failure. 3 4
Since the number of subjects aged 80 and older included in these trials is small, evidence from observational studies may help in deciding whether to treat hypertension in patients at this age. Previous observational studies comprised of people aged 80 and older have found no relation between blood pressure and mortality, 5 and a U shaped relation, 6 or even an inverse relation in which higher blood pressure was associated with lower mortality. 7-9 However, adjustment for confounding factors was made in only one study 9 ; in this study only 35 deaths occurred in those aged over 80.
To determine whether the relation between blood pressure and all cause mortality differs in elderly people older than 85 as compared with younger elderly people and to see whether this relation can be explained by poorer health among those with low blood pressure, we analysed the relation between blood pressure and mortality in a 5 to 7 year study of a cohort of residents of Leiden aged 85 and over; 621 deaths occurred and extensive data on health status at baseline were available.
Subjects and methods
The Leiden 85 plus study is a community based study that was designed to investigate the association between HLA and life expectancy. 10 It contains data on all people aged 85 and over who lived in Leiden on 1 December 1986. There were 1236 cohort members eligible to participate in the study. Of these, 956 agreed to participate, 218 died before they could be visited, 59 declined to cooperate, 2 emigrated, and 1 was not interviewed in error; thus, 94% of all living subjects participated.
Data collection
Subjects were visited at their homes between January 1987...