Exploring the association between cognitive decline and all-cause mortality with blood pressure as a potential modifier in oldest old individuals

Abstract

Few studies have systematically explored the association between cognitive decline and all-cause mortality among oldest old individuals (above 80 years old), and there is limited evidence of blood pressure (BP) as a potential effect modifier. Therefore, this study included 14,891 oldest old individuals (mean age: 90.3 ± 7.5 years); 10,904 deaths and 34,486 person-years were observed. Cognitive scores were calculated using the Chinese version of the Mini-Mental State Examination (MMSE). Cognitive decline was stratified into ten categories (C0-C9). Continuous cognitive scores were used to assess the interactions of modifiers of the cognitive decline and all-cause mortality association and potentially modifiable factors. Potential effect modifiers were explored by age, sex, BP status and hypertension. Cox proportional hazards models were used to evaluate the relationship between cognitive decline and all-cause mortality after adjustments for demographic characteristics, socioeconomic status, lifestyle factors, leisure activities and health conditions. Participants who progressed to severe cognitive impairment from high normal cognitive function (C3), low normal cognitive function (C6), or mild cognitive impairment (C8) had 55%, 56%, and 63% higher mortality risks, respectively, than those who maintained high normal cognitive function (C0). The multivariate-adjusted model indicated that oldest old individuals with a decrease of more than one point in the MMSE score per year had an approximately 4% all-cause mortality risk. The relationship between cognitive decline and mortality was statistically influenced by sex (P = 0.013), high BP in nonagenarians (P = 0.003), and hypertension (P = 0.004) but not by age (P = 0.277). Our findings suggest that periodic screening for cognitive decline and strengthening BP management may be necessary for public health.

Figure 1

Potential effect modifiers of the association of cognitive decline, stratified into ten categories, with mortality after full adjustment for covariates. Adjustments for demographic characteristics (sex and age), socioeconomic status (residence, educational background, current spouse status, and living pattern), lifestyle factors (regular exercise, current smoking, current alcohol consumption, dietary diversity (DD)), leisure activities (housework, reading, watching TV or listening to the radio, keeping a pet and gardening) and health conditions (high blood pressure (BP), disability in activities of daily living (ADL), hypertension, and respiratory disease). Cognitive decline: Ten categories (C0–C9, compared to C0): C0 High normal cognitive function maintenance, C1 High normal cognitive function decline to low normal cognitive function, C2 High normal cognitive function decline to mild cognitive impairment, C3 High normal cognitive function decline to severe cognitive impairment, C4 Low normal cognitive function, maintain function, C5 Low normal cognitive function decline to mild cognitive impairment, C6 Low normal cognitive function decline to severe cognitive impairment, C7 Mild cognitive impairment maintenance, C8 Mild cognitive impairment maintenance, C9 Severe cognitive impairment maintenance.