Study Design and Patient Selection
This cross-sectional study was conducted on participants of Rafsanjan cohort study (RCS); as part of the prospective epidemiological research studies in IrAN (PERSIAN) (21), launched in August 2015 in the Rafsanjan, a region in south east of Iran. Study population was selected via 9990 sampling that had complete habit history (22). Study inclusion criteria were age between 35 and 70 years, male or female. Study protocol was designed according to the Persian cohort study and was approved by the Ethics Committee of Rafsanjan University of Medical Sciences (Ethical codes: ID: IR.RUMS.REC.1399.081).
All participants underwent a standardized interview to completely validated questionnaires containing questions on demography, socioeconomic status, smoking behavior, opium use, alcohol consumption, history of disease, blood pressure, body mass index (BMI) and physical activity. Questionnaires were validated in the PERSIAN cohort study (21). In this study, opium use was defined as self-reported use of opium. Subjects were divided into two groups of non-opium users (NOUs = 7612 subjects), opium users (OUs = 2378 subjects) (22).
CVD prevalence was assessed using self-reported information from the medical history questionnaire. Prevalent CVDs was defined as IHD and MI based on the self-reporting of the participants that a doctor told them they had angina, a myocardial infarction or reported undergoing coronary bypass surgery, balloon angioplasty or stent placement in coronary arteries (22).
Fasting serum total cholesterol, high density lipoprotein cholesterol (HDL cholesterol), low density lipoprotein cholesterol (LDL cholesterol), S.G.O.T (AST), S.G.P.T (ALT), alkaline phosphatase, and triglycerides were measured using a CPALS analyzer (Coultronics, Margency, France) at the Central Laboratory in Cohort center.
Exposure and other covariate assessment
To assess opium use, we used a structured questionnaire in which detailed questions about age at the time of starting opium use, amount and frequency of use (e. g. how many days a week in the case of weekly use), administration routes, opium types, and age the time of quitting for those who had quitted opium use. Routes of administration included opium smoking and oral consumption. Opium types included teriak, Sukhteh, and Shireh. Teriak is a sticky paste which is prepared after air-drying the raw opium (23, 24). Sukhteh is a black dry residue which sticks to the opium pipe after smoking Teriak. Sukhteh is then scraped from the pipe and can be ingested. Shireh is a refined product of opium which is often obtained by boiling a combination of raw opium and Sukhteh in water and filtering the mixture several times. Heroin is another product obtained from opium (23, 24). However, its use among the participants of this cohort was rare, so heroin use was not evaluated in this study.
The chi-square test was used to analyze categorical variables across opium use categories. t -test was used to compare continuous variables among the groups. Logistic regression models were used to investigate the relationships between opium use and IHD and MI prevalence. Confounders were identified using a directed acyclic graph based on subject matter knowledge and the relevant epidemiological literature and were sequentially entered into models according to their hypothesized strengths of association with opium use and IHD and MI. Adjusted model 1 included basic sociodemographic characteristics considered to be most strongly related to both opium use and IHD and MI: age, gender and education years, although not as strongly sociodemographic characteristics. Adjusted model 2 additional adjustment for lifestyle and behavioral factors that were additionally considered to confound opium use – IHD and MI associations. These included, lifestyle confounding variables (tobacco smoking, alcohol drinking) and physical activity level. Adjusted model 3 included all variables in adjusted model 2 and additionally included hypertension , hypercholesterolemia , body mass index and diabetes mellitus, Triglycerides, LDL cholesterol, HDL cholesterol, S.G.O.T (AST) , S.G.P.T (ALT) , Alkaline phosphatase. As these were hypothesized to be potential intermediates on the causal pathways that could explain opium use – IHD and MI disease relationships. In all models, variables of age, education Years , hypercholesterolemia, body mass index (BMI) and, Triglycerides, LDL cholesterol, HDL cholesterol, S.G.O.T (AST), S.G.P.T (ALT), alkaline phosphatase were entered continuously. Also, for current users, duration of use were categorized into quintiles to test for dose-response relationships. Data were analyzed by routes of administration of opium used, also. All analyses were conducted in State V.12. All p-values are two-sided, and p-values < 0.05 and 95% confidence intervals including one were considered as statistically significant.