Associations between risk of overall mortality, cause-specific mortality and level of inflammatory factors with extremely low and high high-density lipoprotein cholesterol levels among American adults

Abstract

Background: The health outcomes associated with extremely low or high plasma concentrations of high-density lipoprotein cholesterol (HDL-C) are not well documented mainly because of the small numbers of participants with such values included in the clinical trials.

Objective: We prospectively investigated the association between extremely low and high HDL-C with: 1) the risk of overall, coronary heart disease (CHD), cerebrovascular and cancer mortality, and, 2) their link with inflammatory factors.

Methods: Analysis was based on subjects ≥18 years old from the National Health and Nutrition Examination Surveys (NHANES). We categorized HDL-C levels as follows: [low HDL-C group ≤30 (extremely low), 30-40 (low), and ≥40 (reference)] [high HDL-C group = 40-80 (reference), 80-100 (high) and ≥100 mg/dl (extremely high). Cox proportional hazard regression models and analysis of covariance accounted for survey design, masked variance and sample weights.

Results: After adjustment for age, race and sex, we found that the very low HDL-C category (<30 mg/dl) had a greater risk of total mortality (risk ratio [RR]: 3.00, 95%CI: 2.20-4.09). RR for CHD and stroke mortality was 2.00 and 2.53, respectively; there was no link between cancer and level of HDL-C (p = 0.235). The association between total mortality, CHD and stroke with the level of HDL-C attenuated but remained significant even after adjustment for demographics, dietary, cardiovascular risk factors and treatment for dyslipidemia (all p < 0.001). After adjustments, subjects with extremely high HDL-C levels had a higher risk of mortalities (all p < 0.001). Mexican-American ethnicity, subjects in the low level of HDL-C (30-40 mg/dl) category had higher risk of mortalities than those with a very low level (all p < 0.001). Concentration of C-reactive protein, fibrinogen and white blood count significantly decreased as the level of the HDL-C increased; these findings were robust after adjustment for demographics, dietary, cardiovascular risk factors and treatment for dyslipidemia (all p < 0.001); further subjects with extremely high HDL-C levels have a greater levels of inflammatory factors (all p < 0.001).

Conclusions: Both extremely low and high HDL-C levels were associated with greater risk of mortalities (total, CHD and stroke) and higher level of inflammatory factors, while there was no link between level of HDL-C and risk of cancer. Moreover, we found evidence of an HDL-C paradox in Mexican-American ethnicity participants.

Keywords: Cancer; Coronary heart disease; High-density lipoprotein cholesterol; Inflammatory factors.