Determinants of serum HDL-C level in a Tehran urban population: the Tehran Lipid and Glucose Study

Decreased serum high-density lipoprotein cholesterol (HDL-C) is one of the most common lipid disorders in patients with coronary artery disease (CAD). Existing evidence suggests that every 1 mg/dL decrease in serum HDL-C increases the risk of CAD by 2-3%. This study was performed in the year 2000 to study HDL-C determinants in a Tehran population.

We studied 9514 subjects (3942 men and 5572 women) aged 20-69 years, who participated in the Tehran Lipid and Glucose Study (TLGS), completed a personal history questionnaire (especially concerning physical activity and cigarette smoking), and underwent a clinical examination including anthropometric and blood pressure measurements. Serum total cholesterol, triglyceride and HDL-C levels were measured, and OGTT was used to define diabetic patients according to WHO criteria. The women had a significantly higher mean HDL-C level than the mean (45 +/- 11 vs 38 +/- 9 mg/dL; p < 0.001); low HDL-C levels (< 35 mg/dL) were observed in 31% of the men and 13% of the women (p < 0.001). Obese subjects (BMI > or = 30 kg/m2) had a significantly lower HDL-C level than the normal subjects (42 +/- 11 vs 44 +/- 11 mg/dL: p < 0.001), and those with truncal obesity (WHR > or = 0.95 in men and > or = 0.8 in women) lower HDL-C levels than the normal subjects (37 +/- 9 vs 39 +/- 10 mg/dL in men and 44 +/- 11 vs 42 +/- 11 mg/dL in women; p < 0.001 for both). Smokers had a significantly lower HDL-C level than non-smokers (38 +/- 10 vs 43 +/- 11 mg/dL; p < 0.001) and a low HDL-C level was twice as common (36.4 vs 18.2%). Passive smokers also had lower HDL-C levels (42 +/- 11 vs 43 +/- 11 mg/dL; p < 0.001). Mean serum HDL-C was significantly lower in hypertriglyceridemic than those with normal triglycerides levels (men: 4 +/- 8 vs 40 +/- 9 mg/dL, p < 0.001; women: 40 +/- 10 vs 47 +/- 11 mg/dL, p < 0.01). Mean HDL-C levels were similar in subjects with different degrees of physical activity, as well as between diabetics and non-diabetics and hypertensive and normotensive subjects. Multiple stepwise regression analysis showed that the determinants of serum HDL-C levels were, in order of entering the model: hypertriglyceridemia (OR 3.4, p < 0.001), male sex (OR 3.1, p < 0.001), cigarette smoking (OR 1.7, p < 0.001), obesity (OR 1.4, p < 0.01), age (OR 0.9, p < 0.05), high WHR (OR 1.2, p < 0.05), and passive smoking (OR 1.1, p < 0.05). Physical activity, hypertension, and diabetes mellitus did not enter the predictive model.

Apart from age and sex which are constitutional, and unmodifiable variables, the determinants of HDL-C level (hypertriglyceridemia, obesity, truncal obesity, cigarette smoking, and passive smoking) can be used in community CAD prevention programmes.