Study Design and Sampling Method
The Hoveyzeh Cohort Study (HCS) is a population-based cohort study designed to assess NCDs in the southwest of Iran(33). This is one of the sites of the Prospective Epidemiological Research Studies in IrAN (the PERSIAN Cohort Study) (34) and recruited 10009 adults (age 35-70 years) from May 2016 to August 2018. Based on the 2016 door-to-door census, 12103 eligible individuals were living in the Hoveyzeh district. Invitations to the cohort site were given by trained inviters one week before the referral day. A phone call was made to remind the invitees the day before the visit. Out of 12103 eligible individuals invited, 8792 were enrolled in the study for the first stage, 982 for the second stage, and 235 for the third stage of invitation. Finally, 10009 individuals entered the study. The overall response proportion was 85.16%.
Inclusion/exclusion criteria of the study participants
Inclusion criteria consisted of: (1) age of 35–70 years old, (2) residence in Hoveyzeh, (3) lack of severe mental disorder and ability to answer the questionnaires without help (4) Not to be deaf and dumb. We excluded participants without data on SES or missing data for MetS.
Definition of the MetS
The criteria for MetS diagnosis were: 1) abdominal obesity (waist circumstance ≥ 102 in men and ≥88 in women), 2) high serum triglycerides (≥150 mg/dL) or take hypertriglyceridemia medications, 3) abnormal serum high-density lipoprotein (HDL) cholesterol (≥40 mg/dL in men and NCDs 50 in women), or take drug treatment for low HDL cholesterol,4) high blood pressure ≥130/85 mmHg, or take hypertension drugs, 5) high fasting plasma glucose (FPG) ≥100 mg/dL, or take hyperglycemia drugs. The presence of at least 3 out of the 5 mentioned criteria used in the case definition constituted a diagnosis of MetS (30).
Components of MetS measurements and quality control of laboratory
Individuals attending the study had been fasting for about 10 to 12 hours on the day of enrollment. Tubes without anticoagulant (clot) were placed at room temperature 30 to 40 minutes before centrifugation under a Class II laminate laboratory hood. During this time, the serum was separated from the rest of the blood. Then, the clot tubes were located into the centrifuge(Sigma, Germany) at 3000 rpm for 10 to 15 minutes. The required serum levels were measured by BT 1500 autoanalyzer (Biotecnica Instruments, Italy). Normal and pathogen control serum samples were defined and RUN for BT 1500 device. Finally, control serum results were evaluated in Westgard and Levy Jennings quality control chart. From these data, mean and SD were calculated. Levy Jennings chart was constructed with x + 2SD as warning limits and x + 3 SD as control limits. The percent coefficient of variation (CV), was defined as SD times 100 divided by the mean value of the results in a set of replicate measurements. Therefore, a smaller CV indicates higher precision. Table 1 represented mean and CV% MetS components.
Table 1 shows precision data obtained for routine biochemical analytes by BT 1500 autoanalyzer.
Analyte
|
Mean
|
CV%
|
HDL
|
30.8
|
2.75
|
Chol
|
152
|
2.70
|
TG
|
110
|
2.28
|
FBS
|
94.4
|
2.71
|
Anthropometric measurements
Anthropometric measurements were taken by trained staff. Height(cm) was measured by a Stadiometer (Seca 206) in a standing position without shoes, shoulders relaxed, facing forward with head and back facing the wall. Weight (kg) was measured with minimal clothing on, by a standing scale (Seca 755). Also, a locked tape meter (Seca) was used for measuring the waist, wrist, and hip circumference (cm).
Blood pressure measurements
At least half an hour before blood pressure measurement, participants should not exercise and have heavy physical activity, have not consumed heavy food, coffee, alcohol, drugs, and stimulant drinks, and have not smoked. Before measuring the first blood pressure, the participant must rest for 1-2 minutes sitting. A Richter sphygmomanometer with a suitable cuff size was used. The blood pressure cuff was neither tight nor too tight on the bare arm. Blood pressure was measured from the right and left arms of the person twice at a ten minutes interval, and when measuring blood pressure, the person's hand was placed on a flat surface such as a table.
SES indicators
We used four indicators to assess SES in this analysis: The Townsend deprivation index, as an area-level indicator of SES, the wealth index, as a household level indicator of SES, and educational level and skill level, as individual-level socio-economic indicators.
The wealth index was calculated according to the information on households’ assets, including freezer, TV, motorbike, cell phone, car, vacuum cleaner, internet access, washing machine, computer, and household utilities consisting of house ownership, number of rooms per capita. A principal component analysis (PCA) was conducted to assign a coefficient to each asset. The sum of the first component scores constructed the wealth scores. Eventually, the scores were converted to 5-ordered categories including poorest, poor, moderate, rich, and richest based on the quintiles (35).
Townsend deprivation index was calculated in four steps: 1) To calculate the percentage of households of non-car ownership, non-house ownership, having unemployed adults and overcrowding, 2) To calculate logged unemployed and logged overcrowds, 3) To calculate Z score of no car, non-homeowners, unemployed, and overcrowd, 4) To calculate Z score of no car + Z score of the non-homeowner + Z score of unemployed + Z score of overcrowding = TDS. Finally, the calculated scores were categorized into five ordinal categories Based on the quintiles including most affluent, affluent, moderate, deprived, most deprived(36).
In our study, occupational classification was done according to the International Standard Classification of Occupations (ISCO-8). Skill level is considered a function of the complexity and range of performing tasks and duties related to an occupation. Four broad and ordered skill levels are used in ISCO-08. Skill Level 1 typically involves performing simple and routine physical or manual tasks. The people categorized in Skill Level 1 may require physical strength and/or endurance. In skill level 2, reading information and performing simple arithmetical calculations are usually essential. Skill level 3 generally requires a high level of literacy, numeracy, and well-developed interpersonal communication skills. Finally, Skill level 4 requires extended levels of literacy and numeracy, sometimes at a very high level, and excellent interpersonal communication skills (37).
Lifestyle measurements
We used International Physical Activity Questionnaire (IPAQ) to measure the physical activity level for the participants. The metabolic equivalent of the task (MET Index) was calculated from this questionnaire. That is the ratio of a person's working metabolic rate relative to his/her resting metabolic rate. One MET is defined as the energy cost of sitting quietly and is equivalent to a caloric consumption of one kcal/kg/hour. A person who has smoked no less than 100 cigarettes during his or her lifetime is defined as a smoker. To determine alcohol abuse among participants, we asked whether they have continually used them in their lifetime. The amount of consumption and its type has also been asked (1).
Statistical analysis
Descriptive statistics measures were performed using mean and standard deviation for quantitative variables, while frequency and percentage were used for categorical variables. Chi-square test, chi-square test for trend, and crude odds ratio used to assess univariate analysis associations. In multivariable analysis, adjusted odds ratios from the unconditional logistic regression model were to measure the association between the study variables. All reported p-values were based on two-tailed tests and compared to a significance level of 0.05. IBM® SPSS® Statistics 26.0 was used for the statistical analysis.