An Overview on Cardiovascular Risks Definitions by Using Survival Analysis Techniques-Tehran Lipid and Glucose Study: 13-Year Follow-Up Outcomes

Risk assessment is an important issue for starting medication for patients. Literature reveals that diabetes, hypertension, dyslipidemia and Body Mass Index (BMI) are among major risk factors for longevity. Since the cut-off points proposed in various sources are generally irrespective of age, sex and race, it has been attempted to validate current definitions for Tehran’s elderly population by using a prospective cohort study. For this purpose, one thousand seven hundred and ninety eight (1,798) individuals above 60 years old were recruited in the primary phase of the Tehran Lipid and Glucose Study (TLGS) during 1998-2001, and were tested for their systolic and diastolic blood pressure, total cholesterol, LDL cholesterol, high density lipoprotein cholesterol (HDL), triglyceride (TG), fasting blood sugar (FBS), 2-h plasma glucose (2HPG) and some other factors at the time of entry to the study. They were followed up for 13 years and their vital statuses were registered (1998-2011).

According to the standard definition of diabetes, dyslipidemia and hypertension, the participants were divided into ill and healthy groups. By using univariate Cox proportional hazard model, a 95% hazard ratio for various risk factors was estimated. Cut-off points of 126 mg/dL for fasting blood sugar or 200 mg/dL for 2HPG for defining diabetes were identified as appropriate points for predicting longevity for elderly males and females. Systolic blood pressure over 140 mmHg or diastolic blood pressure over 90 mmHg or having medication as a definition of hypertension were identified as a significant risk factor for elderly males only. Dyslipidemia which is defined based on Cholesterol>240 or TG>400 or LDL>160 or HDL<35, was not identified as a longevity predictor for elderly men and women. The results showed that BMI>31 Kg/m2 at the time of entry to the study significantly reduced the survival time of women. In conclusion, the definitions of diseases like hypertension and dyslipidemia based on cut-off points don’t classify the Tehran’s elderly population accurately. More investigation in this regard is required.