HDL vs LDL Cholesterol: Key Differences
HDL (high-density lipoprotein) is beneficial "good" cholesterol that helps remove other forms of cholesterol from your bloodstream, while LDL (low-density lipoprotein) is harmful "bad" cholesterol that contributes to atherosclerosis and cardiovascular disease.
Structural and Functional Differences
HDL Cholesterol
- Composition: High-density lipoproteins with high protein-to-lipid ratio
- Function: Anti-atherogenic properties 1
- Removes excess cholesterol from peripheral tissues
- Transports cholesterol back to the liver for excretion (reverse cholesterol transport)
- Has antioxidant and anti-inflammatory properties
- Size: Smaller, denser particles
- Target levels: ≥50 mg/dL in women and ≥40 mg/dL in men 1
LDL Cholesterol
- Composition: Low-density lipoproteins with lower protein-to-lipid ratio
- Function: Atherogenic (promotes atherosclerosis) 1
- Transports cholesterol from the liver to peripheral tissues
- Can deposit in arterial walls, forming plaques
- Particularly dangerous when oxidized
- Size: Larger, less dense particles (though small, dense LDL particles are more atherogenic)
- Target levels: Vary by cardiovascular risk category 1
- Very high-risk: <70 mg/dL
- High-risk: <100 mg/dL
- Moderate-risk: <130 mg/dL
- Low-risk: <160 mg/dL
Health Impact Differences
HDL Cholesterol
- Cardiovascular protection: Higher levels are associated with reduced cardiovascular risk 2
- Mechanism of protection:
- Removes cholesterol from arterial walls
- Reduces inflammation in blood vessels
- Prevents LDL oxidation
- Influencing factors: Low HDL levels are associated with obesity, physical inactivity, smoking, and certain medications 1
LDL Cholesterol
- Cardiovascular risk: Elevated levels are a primary cause of atherosclerosis and cardiovascular disease 1
- Mechanism of harm:
- Deposits in arterial walls
- Triggers inflammatory response
- Forms plaques that can rupture and cause heart attacks or strokes
- Subtypes: Small, dense LDL particles are more atherogenic than larger LDL particles 1
Clinical Significance
- LDL cholesterol is the primary target for lipid-lowering therapy to reduce cardiovascular risk 1
- Non-HDL cholesterol (total cholesterol minus HDL) is a better predictor of cardiovascular risk than LDL alone, as it includes all atherogenic lipoproteins 1
- The ratio of apoB/apoA-I (reflecting the balance between atherogenic and protective particles) may be an even better predictor of cardiovascular risk than traditional lipid measurements 3
- Even at very low LDL levels (<70 mg/dL), HDL remains predictive of cardiovascular events, highlighting its independent protective role 2
Measurement and Calculation
- LDL cholesterol is often calculated using the Friedewald formula:
- LDL = Total cholesterol - HDL - (Triglycerides/5) 1
- This calculation is valid only when triglycerides are <400 mg/dL
- Direct measurement of LDL is available but more costly
- Non-HDL cholesterol (Total cholesterol - HDL) is a simpler calculation that doesn't require fasting and better predicts risk 1
Therapeutic Implications
- For high LDL: Statins are first-line therapy, with potential additions of ezetimibe or PCSK9 inhibitors for high-risk patients 4
- For low HDL: Focus on lifestyle modifications (exercise, weight loss, smoking cessation) as direct HDL-raising medications have not shown consistent cardiovascular benefits 4
Common Pitfalls
- Focusing solely on LDL without considering non-HDL cholesterol or apoB levels
- Assuming all HDL is protective (dysfunctional HDL may not provide cardiovascular protection) 5
- Not recognizing that both the quantity and quality of lipoproteins matter for cardiovascular risk assessment 6
Remember that while HDL and LDL measurements are important for cardiovascular risk assessment, they should be interpreted in the context of overall cardiovascular risk and other risk factors.