For a long time, high-density lipoprotein cholesterol (HDL-C) has been regarded as the "good cholesterol," and the notion that the higher its level, the lower the cardiovascular risk was close to dogma. Yet a growing number of epidemiological studies in recent years have shown that the relationship between HDL-C and mortality risk is not a simple linear one; instead, it takes the intriguing shape of a U: both excessively low and excessively high HDL-C levels may be accompanied by a higher risk of death.
This "HDL paradox" tells us something important: looking only at the total amount of HDL-C may conceal the biological information that matters most.
Against this backdrop, the research teams led by Li Xi and Lu Jiapeng at Fuwai Hospital conducted an in-depth analysis of HDL subclasses and mortality risk based on ChinaHEART, a large prospective cohort study in China.
ProteinT was honored to provide the related assays and technical support for this study, helping the team resolve structural and functional differences of HDL at a finer molecular resolution.
Study Design
The study covered 353 county-level regions across 31 provinces and performed fine phenotyping of HDL particles in 1,585 adults aged 35–75.
Using nuclear magnetic resonance (NMR) technology, the researchers measured the precise content of six core components across four density subclasses (HDL1–HDL4), delivering the first panoramic characterization of the internal composition of HDL in a Chinese population—the technical foundation on which the subsequent breakthrough findings were built.
Key Finding: Small Particles Are the Real Guardians of the Heart
Over a median follow-up of 7.6 years, the study revealed a clear functional divergence within HDL:
Cholesterol, apolipoprotein A1 and other components carried in the larger, more buoyant HDL subclasses (such as HDL1 and HDL2) were positively associated with all-cause mortality—suggesting that these large HDL particles may carry added health risk.
By contrast, the small, dense HDL subclass (HDL4) showed a clear protective effect: the higher its cholesterol, apolipoprotein A1 and related components, the lower the mortality risk. Individuals in the highest apolipoprotein A1 tertile had a 64% lower risk of all-cause death than those in the lowest.
Solving the U-Shaped Puzzle
These findings offer a plausible explanation for the HDL paradox that has long puzzled the field:
● At very low HDL-C: the rise in mortality risk is mainly attributable to an insufficient pool of protective small HDL particles
● At very high HDL-C: the increased risk may stem from an excess of harmful large HDL particles
A marked sex difference also emerged: the protective effect of small HDL particles was more pronounced in women, which may partly explain why men generally face a higher risk of cardiovascular disease.
Clinical Implications and Future Directions
These findings carry far-reaching implications for the prevention and management of cardiovascular disease:
For risk assessment, conventional HDL-C testing alone may no longer be sufficient to predict risk accurately; greater attention should be paid to HDL subclass distribution, and in particular to the proportion of small HDL particles.
For therapeutic strategy, drugs that simply raise total HDL-C have shown limited benefit; future development should shift toward selectively increasing beneficial small HDL particles while keeping harmful large HDL particles in check.
For preventive medicine, the study underscores the importance of precision intervention: people with different HDL subclass profiles may require differentiated management strategies. Application of this technology platform provides key technical support for moving lipoprotein research from the macro level of total quantity to the micro level of composition.
For the general public, this study changes the way we have traditionally thought about HDL and delivers a clear message: there is no need to chase a high HDL-C number for its own sake. A balanced diet, regular physical activity and other healthy lifestyle habits remain the foundation of cardiovascular health.
