- Study Population
Tehran Lipid and Glucose Study (TLGS) is a community-based prospective cohort study conducted on an Iranian urban population in Tehran. The study aims to determine the prevalence and incidence of non-communicable diseases and related risk factors among individuals aged ≥ 3 years and promote a healthy lifestyle and programs for the prevention of NCD. The study has been established in two phases including the first (1999–2001: n = 15005) and the second (2001–2005; n = 3550) and is designed to keep on for at least 20 years on the triennial basis. The design and methodology of the TLGS study have been reported elsewhere (19). Since the detail of the data regarding the cardiovascular status at the recruitment time was available from the phase II, the current study was designed on 7490 individuals aged 28–85 years who participated in the second phase of the TLGS study (phase I = 5716 and phase II = 1774). From this number, we excluded those with prevalent CVD (i.e. participants with a history of myocardial infarction, angioplasty, coronary artery bypass graft (CABG) or stroke, (n = 546)), prevalent T2DM defined as self-reported use of diabetes-lowering medication (n = 856) and prevalent end-stage renal disease (ESRD) defined by estimated Glomerular Filtration Rate (eGFR) < 15 mL/min/1.73 m2 (n = 1). After excluding those with missing data at baseline for creatinine (Cr), fasting plasma glucose (FPG), 2-hour post-challenge plasma glucose (2 h-PCG), body mass index (BMI), waist circumference (WC) and smoking status (n = 1864, considering overlap features between missing values) as well as participants with missing data during follow-up on Cr (n = 32), FPG, 2 h-PCG (n = 718) and CVD status (n = 203), 3270 individuals were eligible for the current study during 6-year follow-up until March 2011. In line with the risk assessment tool, no one died from non-cardiovascular causes during the follow-up period.
To investigate the long-term effect of the risk assessment tool for prediction of CCD, from a total of 4223 individuals, we excluded prevalent cases of CVD, T2DM and ESRD and those with missing data on covariates using the above approach. 3240 individuals remained for the analysis during 9-year follow-up until March 2018 (Supplementary Fig. 1). This study was approved by the Institutional Review Board (IRB) of the Research Institute for Endocrine Sciences (RIES), Shahid Beheshti University of Medical Sciences, Tehran, Iran, and all participants provided written informed consent.
- Clinical And Laboratory Measurements
Information on demographic data, family history of premature CVD and T2DM, current smoking status and medication history were obtained by a trained interviewer using a standard questionnaire. Detail for anrhtropometric measurments including height, weight and WC was reported elsewhere. A blood sample was taken from all study participants between 7:00 and 9:00 AM after 12 to 14 hours overnight fasting. More detail for laboratory measurmnrts including FPG, 2 h-PCG and seum creatinin was addressed previously (19).
- Definition Of Variables
BMI was calculated as weight (kg) divided by height (m2). A positive family history of premature CVD for the study participant was considered as having previously diagnosed CVD in first-degree male and female relatives aged ˂55 and ˂65 years, respectively. The current smoker was defined as who smokes cigarettes daily or occasionally.
A. Type 2 Diabetes
T2DM was defined as FPG ≥ 7 mmol/L, 2 h-PCG ≥ 11.1 mmol/L or use of anti-diabetic medications.
B. Chronic Kidney Disease
CKD was defined as eGFR < 60 mL/min/1.73 m2, provided by the Modification of Diet in Renal Disease (MDRD) (20, 21).
C. Cardiovascular Disease
According to the previously published article about CVD outcomes in the TLGS cohort (22), each participant is followed-up for any medical event leading to hospitalization during the previous year by telephone call. They were asked for any medical conditions by a trained nurse and later, a trained physician collected complementary data regarding that event during a home visit and by the acquisition of data from medical files. The collected data were then evaluated by an outcome assessment committee consisting of an internist, endocrinologist, cardiologist, epidemiologist, and other experts, if required, to assign a specific outcome for every event. In the current study CHD events included cases of definite and probable MI, unstable angina, angiographic proven CHD and CHD death. Stroke was also defined as definite or possible stroke or transient ischemic attack. Finally, CVD was clarified as a composite measure of any CHD events, stroke or cerebrovascular death.
D. Chronic Cardio-metabolic Disease
CCD was defined as the diagnosis of either T2DM, CKD or CVD during the follow-up period.
- Risk Tool For Chronic Cardio-metabolic Disease
To evaluate the CCD outcome, the risk tool was developed on 6780 Dutch men and women (aged 28–85 years) based on three population-based cohorts: the Rotterdam study(n = 4018), the Hoorn study (n = 627) and the Prevention of Renal and Vascular End-stage Disease (PREVEND; n = 2135) (16). The sex-stratified model including age, BMI, WC, use of antihypertensive, current smoking, parent and/or sibling with MI or stroke (age < 65 years), and Parent and/or sibling with diabetes were developed using logistic regression (Supplementary Table 1). The 7-year risk of CCD was calculated for each subject according to the original risk assessment tool recommended by Alssema et.al (16) for each TLGS men and women.
- Statistical analysis
Baseline characteristics of respondents (those with complete data) and non-respondents (those with missing data of covariates or loss to follow-up) were expressed as mean (standard deviation) and number (%) for categorical variables. For covariates with a skewed distribution, the median (interquartile range: IQR) was reported. A comparison of baseline characteristics between men and women was done by the Student’s t-test for normally distributed continuous variables, Maan -Whitney u test for skewed variables, and the chi-squared test for categorical variables. To evaluate the external validity of the risk equation, Area under the curve (AUC) and Hosmer–Lemeshow chi-square were applied to determine the discrimination and calibration of these predictor models, respectively. According to the Hosmer et.al (23) criteria, the AUCs 0.5–0.7, 0.70–80, 0.80–0.90 and ≥ 0.90 indicated poor, acceptable, excellent and outstanding discrimination, respectively. To show the calibration in detail, the observed risk was plotted versus the mean of predicted probabilities using the calibration belt Stata module (24). Besides, the observed to an expected ratio (O/E) for the CCD outcome was calculated; ratio < 1 indicated overestimation and > 1 indicated underestimation of the risk.
We also recalibrated the risk assessment tool for the TLGS cohort characteristics by adjusting the intercept of the model; the same predictors with the same regression coefficients of the original model were fixed while the intercept was estimated as the free parameters (25). Using the above statistical approach, we repeated our data analysis for those participants with a 9-year follow-up. To compare the discrimination measurement of the risk assessment tool with other available non-invasive prediction models for the CVD outcome, we used the Gaziano et.al. (13) risk score. Statistical analysis was performed using STATA version 14 (StataCorp LP, College Station, Texas), statistical software. p < 0.05 were considered as statistically significant.