Low blood pressure and five-year mortality in a Stockholm cohort of the very old: possible confounding by cognitive impairment and other factors.

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Abstract
OBJECTIVES: Low blood pressure has often been reported to be related to excess mortality in people over the age of 75 years. This study examined whether other predictors may account for the association. METHODS: A community-based cohort of 1810 people who were aged 75 years and older was followed for 5 years. RESULTS: The relative risk of death was 1.39 (95% confidence interval [CI] = 1.11, 1.73) for people with systolic pressure lower than 130 mm Hg and 1.21 (95% CI = 1.02, 1.43) for those with diastolic pressure lower than 75 mm Hg, compared with corresponding reference groups, when all other variables were simultaneously considered in Cox proportional hazards models. The observed association was present mainly in subjects with at least two of the three conditions (cardiovascular disease, limitation in activities of daily living, or cognitive impairment). The effect of low diastolic pressure on mortality was also significant in those with only cognitive impairment. CONCLUSIONS: Preexisting cardiovascular disease, limitation in activities of daily living, and, more important, cognitive impairment may be responsible for the association of low blood pressure with increased mortality in the very old in that they cause both reductions in blood pressure and excess deaths.