Study Participants
This study was a subset of the China H-type hypertension registry study (No. ChiCTR1800017274), a real-world, observational study conducted in Wuyuan county in Jiangxi province of China from March 2018 to August 2018. A detailed description of the China H-type hypertension registry study has been previously published[15]. Eligible participants were male and female individuals aged ≥ 18 years old with hypertension, excepting those with psychological or nervous system diseases resulting in an inability to demonstrate informed consent. All participants signed informed consent before entering the study. The study was approved by the Ethics Committee of Anhui Medical University Biomedical Institute (No.CH1059).
As a result, a total of 14,234 participants with hypertension were recruited for the study. After excluding participants without mini-mental state examination (MMSE) data (n = 3,945), 10,289 participants were finally included in the present cross-sectional study for analysis.
Data collection and variable definitions
Demographic information (e.g., age, sex, and education), living conditions (e.g., current smoking, current drinking, midday napping, sleeping, economic level, labor intensity, and psychological stress), dietary habit (e.g., cooking oil, bean products, meat, fruit, and vegetables), self-reported medical history (e.g., diabetes, stroke, coronary heart disease [CHD], chronic renal disease [CKD], and malignant tumor), and medication history (e.g., antihypertensive, glucose-lowering, and lipid-lowering drugs) from all participants were collected using a standard questionnaire by trained staffs.
Current smoking was defined as smoking ≥ 1 cigarette per day for 1 year or more or a cumulative smoking amount ≥ 360 cigarettes per year. Current drinking defined as drinking alcohol an average of at least two or more times a week over a year. Economic level was subjectively assessed by participants based on comparision with local residents, which included “good”, “medium”, and “poor”. Labour intensity was reflected in self-reported physical burden at work, including light labour (mild), tired or heavy labour (moderate), extremely tired or heavy labour (severe). Psychological stress was referred to the participant's anxiety and emotional tension caused by various reasons such as work problems and health problems, which included “mild”, “modrate”, and “severe”. Sleep duration was assessed by the question: “How many hours on average do you sleep per night?” Mean sleep duration was categorized into 3 groups:<5h, 5–8, and >8hours. Midday napping was assessed by asking “Did you have midday napping habit?” with the following responses: “yes”, “no”.
Physical indicators such as height, weight, and WC were measured twice, and the average values were calculated as the corresponding values. Height was measured using a standard right-angle device and a fixed vertical ruler to the nearest 0.1 cm. Bodyweight was measured using the Omron body fat and weight measurement device from Japan to the nearest 0.01 kg. WC was measured using a tape to measure the minimum circumference at the midpoint between the costal margin and iliac crests (at the umbilicus level) to the nearest 0.1 cm. Blood pressure (BP) was measured three times on the right arm positioned at the heart level using an electronic BP monitor (Omron HBP-1300; OMRON, Japan) after a rest for 5 min, with a 30 s interval between measurements, and three measurements of systolic blood pressure (SBP) and diastolic blood pressure (DBP) were averaged as the corresponding BP values for analysis. BMI was calculated as the weight (kg) divided by the squared height (m2). In addition, WWI was calculated as WC (cm) divided by the square root of weight (kg)[16].
Hypertension was defined as seated resting SBP ≥ 140 mmHg or DBP ≥ 90 mmHg or the use of antihypertensive medications at screening[17]. Diabetes mellitus was defined as a self-reported physician diagnosis of diabetes or the use of glucose-lowering drugs or fasting blood glucose (FBG) concentration ≥ 7.0 mmol/L.
Laboratory tests
Blood samples were collected after ≥ 8 h fasting and delivered to a standardized laboratory within 24 h of sampling. Laboratory indicators include plasma homocysteine (Hcy), FBG, fasting total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), uric acid (UA), and creatinine (Cr) were detected from all participants. The estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation[18]. All laboratory measurements followed a standardization and certification program.
Cognitive assessment
The cognitive function was evaluated using the Chinese version of the MMSE scale[19], which involves a broad series of cognitive domains, including language and visuospatial construction, short-term verbal memory, calculation and attention, immediate recall, and orientation. Correct answers to all questions on the MMSE scale were rated as a maximum score of 30, representing the best cognitive function level. The MMSE score < 24 for participants with secondary school or above education setting (≥ 7 years of education), < 20 for those with primary school (1–6 years of education), and < 17 for illiterate participants were defined as dementia.
Statistical analysis
Continuous variables were presented as mean ± standard deviation (SD), and categorical variables were expressed as frequency (n) and percentage (%). The characteristic differences by WWI quartiles were contrasted using one-way analysis of variance (ANOVA) tests for continuous variables or Chi-square tests for categorical variables. The associations between WWI and MMSE and dementia were analyzed using multivariable linear regression and multivariable binary logistic regression, respectively. In addition, the results were described as β coefficients and odds ratios (ORs) with 95% confidence intervals (CIs). We conducted three levels of adjustment models for the regression analysis: model 1was adjusted for none; model 2 was adjusted for age and sex; and model 3 was adjusted for age, sex, BMI, SBP, DBP, Hcy, FPG, TC, TG, HDL-C, LDL-C, UA, eGFR, diabetes, stroke, CHD, CKD, malignant tumor, antihypertensive drugs, glucose-lowering drugs, lipid-lowering drugs, current smoking, current drinking, midday napping, sleeping duration, economic level, labor intensity, psychological stress, cooking oil, bean products, meat, fruits, and vegetables. These covariables adjusted in the regression models were selected due to clinical importance, statistical significance in the univariable analysis, and the potential confounder effect estimates individually changed by at least 10%. Dose-response relationship between WWI and MMSE and dementia were evaluated using a generalized additive model (GAM) and a fitted smoothing curve (penalized spline method). Additionally, possible modifications of the association with dementia were evaluated using stratified analyses and interaction testing.
R statistical package (http://www.r-proje.ct.org) and Empower (R) software (www.empow.erstats.com) were used for statistical analyses. Statistical significance was defined as a two-tailed P < 0.05.