The Age-Dependent Relationship between Blood Pressure and Cognitive Impairment: A Cross-Sectional Study in a Rural Area of Xi'an, China

Background Hypertension is a modifiable risk factor for cognitive impairment, although the relationship between hypertension and cognitive impairment is not fully understood. The objective of this study was to investigate the effect of age on the relationship between blood pressure and cognitive impairment. Methods Blood pressure and global cognitive function information was collected from 1799 participants (age 40-85) who lived in a village in the suburbs of Xi'an, China, during in-person interviews. Cognitive impairment was defined as a Mini-Mental State Examination (MMSE) score lower than the cutoff value. The effect of age on the relationship between blood pressure parameters [systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MABP), and high blood pressure (HBP, SBP >= 140 mm Hg and/or DBP >= 90 mm Hg)] and cognitive impairment was analyzed by logistic regression models using interaction and stratified analysis. Blood pressure and age were regarded as both continuous and categorical data. Results A total of 231 participants were diagnosed as having cognitive impairment based on our criteria. Interaction analysis for the total population showed that SBP (when regarded as continuous data) was positively correlated with cognitive impairment (OR = 1.130 [95% CI, 1.028-1.242] per 10mmHg, P = 0.011); however, the age by SBP interaction term was negatively correlated with cognitive impairment (OR = 0.989 [95% CI, 0.982-0.997] per 10mmHgxyear, P = 0.006), indicating that the relationship between SBP and cognitive impairment was age-dependent (OR = 1.130x0.989((age-55.5)) per 10mmHg, 40 <= age <= 85). When the blood pressure and age were considered as binary data, the results were similar to those obtained when they were considered as continuous variables. Stratified multivariate analysis revealed that the relationship between SBP (when regarded as continuous data) and cognitive impairment was positive for patients aged 40-49 years (OR = 1.349 [95% CI: 1.039-1.753] per 10mmHg, P = 0.025) and 50-59 years (OR = 1.185 [95% CI: 1.028-1.366] per 10mmHg, P = 0.019), whereas it tended to be negative for patients aged 60-69 years (OR = 0.878 [95% CI: 0.729-1.058] per 10mmHg, P = 0.171) and >= 70 years (OR = 0.927 [95% CI: 0.772-1.113] per 10mmHg, P = 0.416). Results similar to those for SBP were obtained for DBP, MABP and HBP as well. Subsequently, SBP, DBP and MABP were transformed into categorical data (SBP<140mmHg, 140mmHg <= SBP<160mmHg, and SBP >= 160mmHg; DBP<90mmHg, 90mmHg <= DBP< 100mmHg, and DBP >= 100mmHg; MABP<100mmHg, 100mmHg <= MABP<110mmHg, and MABP >= 110mmHg), and the stratified multivariate analysis was repeated. This analysis showed that the age-dependent association continued to exist and was especially prominent in the SBP >= 160 mmHg, DBP >= 90 mmHg and MABP >= 110 mmHg groups. Conclusions Elevated blood pressure is positively correlated with cognitive impairment in the middle-aged, but this positive association declines with increasing age. These results indicated that specific blood pressure management strategies for various age groups may be crucial for maintaining cognitive vitality.