Study design and setting
We conducted a case-cohort study nested in the RaNCD cohort The RaNCD study which is a first cohort study on Kurdish population, on aged 35–65 years living in Ravansar city, Kermanshah province, Western- Iran which started in October 2014. The RaNCD cohort study is a component of the PERSIAN (Prospective Epidemiological Research Studies in Iran) mega cohort study that was approved by the Ethics Committees in the Ministry of Health and Medical Education, the Digestive Diseases Research Institute, Tehran University of Medical Sciences, Iran. The details of this study were described in previous studies [15, 16]. In this study, all recruitment phase participants included, which was surveyed from October 2014 to January 2017 and followed until January 2021 (n = 4764 men and 5258 women). The RaNCD cohort study was approved by the Ethics Committee of Kermanshah University of Medical Sciences (No: KUMS.REC.1394.318).
Participants
Among the RaNCD participants, 3300 of them were not included in the study for the following reasons: 1) participants with CVDs (n = 1709), type 2 diabetes (n = 870), hypertension (n = 1579), cancer (n = 83), and thyroid diseases (n = 763); 2) pregnant women (n = 138); 3) energy intake less than 800 Kcal/day or more than 4200 Kcal/day (n = 737). After excluding participants with missing data, overall, 6747 participants were included into this study.
Measurements
This current study was obtained demographic data including age, sex, smoking status, and physical activity, as well as, medical history, medication, anthropometric indices, blood pressure, and biochemical analysis.
Anthropometry
All participants’ height were measured by the automatic stadiometer BSM 370 (Biospace Co., Seoul, Korea) with a precision of 0.1 cm in standing position without shoes. InBody 770 device (Inbody Co, Seoul, Korea) was applied to measure the weight and body fat mass (BFM) of participants with the least clothing and without shoes. To determine obesity, body mass index (BMI) was calculated by dividing weight in kilogram to square height in meter2, after that BMI more than 30 kg/m2 as obesity. Waist circumference (WC) was measured using non-stretched and flexible tape in standing position at the level of the iliac crest.
Blood pressure
In RaNCD cohort study, conventional sphygmomanometry and auscultation of the Korotkoff sounds was used to measure systolic and diastolic blood pressure (SBP and DBP) in sitting position after at least 4–5 minutes of rest. The blood pressure measuring was conducted two times with 10 minutes interval and the mean of them was calculated and reported as the final blood pressure [15].
Biochemical analysis
25 cc blood samples were collected from all RaNCD participants. The serum and whole blood samples were subdivided and were stored at -80◦C the RaNCD cohort laboratory until analysis. Serum fasting blood sugar (FBS) was measured by glucose oxidase method. Total cholesterol (TC), high-density lipoproteins (HDL), triglyceride (TG) and low- density lipoproteins (LDL) concentration were measured by enzymatic kits (Pars Azmun, Iran) [15].
Obesity phenotypes
We defined MUO presence of BMI > 30 kg/m2 and at least two metabolic disorder according to the International Diabetes Federation (IDF) statement [17] as follow: HDL < 40 mg/dl in men and < 50 mg/dl in women; increased TG > 150 mg/dl; SBP > 130 mmHg or DBP > 80 mmHg or antihypertensive medication; and FBS > 100 mg/dl or medication for diabetes. Also, MHO was defined BMI > 30 kg/m2 and having at most one metabolic disorder mentioned in the previous sentences, as well as, MUNO phenotype was considered presence of BMI < 30 kg/m2 and at least two metabolic disorder. In addition, MHNO participants were related to healthy participants without obesity and metabolic disorder.
Outcome measurement hypertension incidence
The hypertension was defined by codes I10 of the International classification of diseases Tenth Edition (ICD-10), which included SBP/DBP ≥ 140/90 mmHg and/or using anti-hypertensive medications in the time interval between baseline (first phase of Ravansar cohort which has been conducted from 2014) and hypertension diagnosis (from 2015 to 2021), which the overall duration of the follow-up was 391162 person-months.
Statistical analysis
Statistical analysis was performed using Stata, version 14 (Stata Corp, College Station, TX). Mean ± standard deviation (SD) and frequency percent was used to report baseline characteristics of studied participants. To compare results of baseline characteristics among different obesity phenotypes, one-way analysis of variance (ANOVA) was used for continuous variables, and a Chi-square test was used for categorical variables.
Incidence rate (IR) calculated based on 1000 person/months Cox proportional hazards regression model were used to calculate hazard ratios (HRs) stratified by obesity phenotypes, with hypertension as the event and the time interval between baseline (first phase of RaNCD cohort) and hypertension diagnosis as the time covariate. The models of adjusted for confounding variables including age, sex, physical activity, smoking and energy intake, and reported as HR with 95% confidence interval (CI).