Yan Sun

High-density lipoprotein (HDL) contributes to reverse cholesterol transport, which is 1 of the main explanations for the described inverse association between HDL-cholesterol (HDL-C) and atherosclerotic cardiovascular disease (ASCVD) risk. However, efforts to therapeutically raise HDL-C levels with niacin, fibrates, or cholesteryl ester transfer protein inhibitors have not demonstrated a reduction in ASCVD events when compared with placebo among individuals treated with statins. Furthermore, mendelian randomization studies suggest that HDL-C is unlikely to be a direct biologic variable impacting ASCVD risk. More recently, observations from well-conducted epidemiologic studies have indicated a nonlinear U-shaped relationship between HDL-C and subclinical atherosclerosis, and that very high HDL-C (≥80 mg/dL in men, ≥100 mg/dL in women) is paradoxically associated with higher all-cause and ASCVD-related mortality. These observations suggest that HDL-C is not a universal protective factor for atherosclerosis. Thus, there are several opportunities for reframing the contribution of HDL-C to ASCVD risk and related clinical calculators. Here, we examine our growing understanding of HDL-C and its role in ASCVD risk assessment, treatment, and prevention. We discuss the biological functions of HDL-C and its normative values in relation to demographics and lifestyle markers. We then summarize original studies that observed a protective association between HDL-C and ASCVD risk and more recent evidence indicating an elevated ASCVD risk at very high HDL-C levels. Through this process, we advance the discussion regarding the future role of HDL-C in ASCVD risk assessment and identify knowledge gaps pertaining to the precise role of HDL-C in atherosclerosis and clinical ASCVD.