Study population
The NHANES is an ongoing, nationally representative study in the United States that tracks participants biennially since 1999, accumulating data on the health and nutritional conditions of non-institutionalized US citizens. The protocol of the NHANES study received approval from the Research Ethics Review Committee of the National Centers for Health Statistics (NCHS), and each participant provided their written informed consent. Interviews take place in the homes of the participants, which are then followed by examinations and lab tests performed in mobile examination centers. The study collected information on demographic characteristics, dietary habits, physical health assessments, and questionnaire responses. Skilled interviewers conducted an in-home interview and obtained automated data.
The data for this study was sourced from five continuous NHANES cycles from 2007 to 2016. A total of 50,588 participants were initial included. Exclusions were made for individuals under the age of 20, pregnant individuals, and those lacking data on the LE8 metrics components, as well as participants without hypertension or unknown hypertension status. After removing 5 missing deaths, the study included a total of 8,448 patients (Fig. 1).
Flow chart of the sample collection in this study
Assessments of CVH
The LE8 scoring algorithm comprises four health behaviors (diet, physical activity, nicotine exposure, and sleep duration) and four health factors (body mass index [BMI], non-high-density lipoprotein cholesterol, blood glucose, and blood pressure). Detailed algorithms for calculating the LE8 scores for each metric using NHANES data have been previously published and can be found in Table S1. Briefly, each of the eight CVH metrics was assigned a score ranging from 0 to 100 points. The overall LE8 score was calculated as the unweighted average of these eight metrics. Each individual’s score for each of the 8 CVH metrics was determined on a scale of 0 to 100 points using the American Heart Association (AHA) algorithm. The overall CVH score for each individual was calculated by adding up the scores for each of the 8 metrics and then dividing the total by 8, resulting in an LE8 score ranging from 0 to 100. Participants with an LE8 score of 80–100 were classified as having high CVH, scores of 50–79 indicated moderate CVH, and scores of 0–49 indicated low CVH [7].
Definition of hypertension
In accordance with the blood pressure measurement protocol established by the AHA, a trained examiner recorded the blood pressure. The average systolic and diastolic blood pressure values were obtained by taking three consecutive measurements and reported accordingly. If the patient has multiple blood pressure readings, the average is utilized to diagnose hypertension. Consistent with previous research analyzing the NHANES database, hypertension was defined as meeting any of the following criteria: (1) average systolic blood pressure (SBP) ≥ 140 mmHg, (2) average diastolic blood pressure (DBP) ≥ 90 mmHg, (3) self-reported hypertension, or (4) individuals taking prescribed antihypertensive medications. The threshold of 140/90 mmHg aligns with the guideline set by the International Society of Hypertension.
Definitions of variables of interest
In this study, we selected a priori covariates based on clinical relevance and previously published research. Demographic variables measured using the self-reported questionnaire included age, sex, and race and ethnicity (Mexican American, non-Hispanic Black, non-Hispanic White, and Other). Levels of educational attainment were classified into three levels: less than high school, high school or equivalent, and high school above. The poverty income ratio (PIR) is an indicator that measures the ratio of household income to the poverty threshold and are classified as PIR ≤ 1.3, 1.3 3.5. Marital status was categorized as unmarried and married. Individuals who have smoked less than 100 cigarettes throughout their life are categorized as never smokers. People who have smoked more than 100 cigarettes throughout their life are deemed as current smokers, while those who have smoked more than 100 cigarettes but have since stopped are identified as former smokers. Self-reported CVD diseases included angina, congestive heart failure, coronary heart disease, myocardial infarction, and stroke. History of malignancy was obtained by questionnaire. Examination and laboratory measurements consisted of BMI, waist circumference, SBP, and DBP. Diabetes was categorized based on criteria that included a patient’s self-reported diagnosis, a fasting plasma glucose level equal to or exceeding 7.0 mmol/L, an HbA1c concentration of 6.5% or above, or the use of medication for blood glucose control. The use of medications such as antihypertensive drugs, antidiabetic medications, and statins was also documented.
Ascertainment of mortality
The death status and cause of death were established by linking to the NHANES with the National Death Index’s public access files up until December 31, 2019. The International Classification of Disease (ICD) was used to specify the cause of death. Mortality due to CVD was characterized as deaths caused by heart diseases (ICD-10 codes I00-I09, I11, I13, I20-I51) and cerebrovascular diseases (ICD-10 codes I60-I69).
Statistical analysis
The NHANES uses design weighting to produce accurate national estimates. Baseline characteristics of the study population were stratified by CVH categories, with continuous variables presented as survey-weighted mean and categorical variables presented as survey-weighted percentage (%), with corresponding confidence intervals (CIs). We used the Variance Inflation Factor (VIF) to evaluate multicollinearity among all variables. Any covariates that had a VIF exceeding 5 were eliminated from our consideration. Variables with a missing value of more than 10% were only used for statistical analysis and were not included in logistic regression analysis. For each category of CVH level, we calculated age-standardized mortality estimates along with their 95% CIs. Kaplan–Meier plots were generated to display mortality risk by CVH categories. We adopted multivariate Cox proportional hazards regression to generate hazard ratios (HRs) and 95% CIs of all-cause and CVD mortality with the low CVH category as a reference. A potential variable was incorporated if it was either associated with all-cause mortality or resulted in a change of more than 10% in any effect measure [12]. Three multivariate COX regression model was developed. Model 1 was a crude model unadjusted for potential confounders. Model 2 was adjusted for sex, age, race/ethnicity, education level, marital status, PIR, BMI, waist circumference. Model 3 was further adjusted for history of malignancy, history of CVD, history of diabetes, smoking status, DBP, and SBP. The possible modifications of the association between LE8 and all-cause mortality were performed in several subgroups. We explored the relationship between LE8 and all-cause mortality in different subgroups including age (2, 18.5 to 24.9 kg/m2, 25.0 to 30.0 kg/m2, ≥ 30 kg/m2), education level, marital status, smoking status (never, former, now), history of malignancy, CVD, diabetes. To assess effect measure modification, we incorporated an interaction term into the model for each analysis. To examine linearity and investigate the shape of the dose–response relationship between LE8 and all-cause and CVD mortality in hypertensive patients, a Cox regression was conducted using a restricted cubic spline with 4 knots (5th, 35th, 65th, and 95th percentiles). The likelihood ratio test was employed to assess nonlinearity. To ensure the reliability of our findings, we conducted two sensitivity analyses. Firstly, in order to minimize the potential bias of reverse-causality, individuals who died within the initial 24 months of follow-up period were excluded. Secondly, we adopted the most recent guidelines from the AHA, which define hypertension as an SBP of ≥ 130 mmHg and/or DBP of ≥ 80 mmHg [13]. All the above statistical analyses were performed using R software (http://www.Rproject.org, version 4.1.2). Two-sided P
Rohit Malhotra is a medical expert and health journalist who offers evidence-based advice on fitness, nutrition, and mental well-being. His articles aim to help readers lead healthier lives.
