Summary
LDL (low-density lipoprotein) cholesterol is the primary carrier of cholesterol to peripheral tissues and the principal driver of atherosclerosis — the hardening and narrowing of arteries that causes heart attacks and strokes. Lowering LDL is the most evidence-based intervention in cardiovascular prevention, with randomised trial data showing that every 1 mmol/L reduction in LDL reduces major cardiovascular events by approximately 22%.
LDL delivers cholesterol to cells throughout the body via LDL receptors. When LDL levels are high, excess LDL enters the arterial wall, where it is oxidised and taken up by macrophages, forming foam cells — the earliest lesions of atherosclerosis. Over decades, these plaques enlarge, become unstable, and can rupture, triggering a heart attack or stroke.
The causal relationship between LDL and cardiovascular disease is one of the best-established in medicine, supported by Mendelian randomisation studies, population genetics, statin trials, and PCSK9 inhibitor studies. Lifetime cumulative LDL exposure is now considered the key determinant of cardiovascular risk.
UK NICE guidelines recommend an LDL target of < 1.8 mmol/L for very high-risk patients (existing CVD) and < 3.0 mmol/L for primary prevention. Trupoint tests support monitoring both baseline and treatment-response LDL.
What It Is
LDL (low-density lipoprotein) particles are formed in the bloodstream from VLDL remnants after triglyceride removal. Each LDL particle contains a single molecule of apolipoprotein B-100 (ApoB), which binds the LDL receptor on cell surfaces. LDL particle number — reflected by ApoB — is arguably a better predictor of cardiovascular risk than LDL-C, as particles with the same LDL-C level but more particles (small dense LDL) carry higher risk.
LDL cholesterol is calculated using the Friedewald equation: LDL-C = total cholesterol − HDL-C − (triglycerides ÷ 2.2). This equation is inaccurate when triglycerides > 4.5 mmol/L — direct LDL measurement is required in this case.
Target levels: general population < 3.0 mmol/L; high CVD risk (QRISK3 ≥ 10%) < 3.0 mmol/L; established CVD or very high risk < 1.8 mmol/L (NICE); < 1.4 mmol/L for those with recent ACS (ESC).
Functions
Primary atherosclerosis driver
LDL deposits cholesterol into arterial walls, initiating and propagating the atherosclerotic plaques that cause heart attacks and strokes.
Cholesterol delivery to cells
LDL's physiological role is to deliver cholesterol to cells that cannot synthesise enough — including rapidly dividing cells and steroidogenic tissues.
Primary cardiovascular treatment target
Lowering LDL is the single most evidence-based cardiovascular intervention — each 1 mmol/L reduction reduces major events by ~22%.
Familial hypercholesterolaemia marker
Very high LDL (> 5.0 mmol/L) in the absence of other risk factors should trigger genetic testing for FH.
Reference Ranges
LDL Cholesterol
Measured in mmol/L| Status | Range (mmol/L) | Range (mg/dL) | What it means |
|---|---|---|---|
| Optimal | < 3.0 | < 116 | Desirable LDL for primary prevention — low cardiovascular risk. |
| Borderline | 3.0–4.9 | 116–190 | Elevated — assess overall cardiovascular risk and consider lifestyle or medication. |
| High | ≥ 5.0 | ≥ 193 | Significantly elevated — warrants active management and possible familial hypercholesterolaemia investigation. |
| Very high | ≥ 7.5 | ≥ 290 | Severe elevation — likely familial hypercholesterolaemia. Urgent referral. |
LDL targets depend on baseline CVD risk. NICE recommends < 1.8 mmol/L for established CVD; < 3.0 mmol/L for primary prevention with QRISK3 ≥ 10%. LDL-C calculated via Friedewald equation is inaccurate when triglycerides > 4.5 mmol/L.
Symptoms of Imbalance
Elevated LDL is entirely asymptomatic until complications develop — years of silent plaque growth precede cardiovascular events.
- Very low LDL (< 1.0 mmol/L) from statin therapy is generally well tolerated
- Rarely: very low LDL associated with haemorrhagic stroke risk at extremely low levels
- Usually completely asymptomatic
- Tendon xanthomata (nodules over Achilles and knuckle tendons) in FH
- Xanthelasma (eyelid deposits) in severe elevation
- Corneal arcus in young adults with FH
- Angina from coronary artery disease after years of elevated LDL
Causes of Imbalance
- Statin therapy (intended effect — reduces LDL by 30–50%)
- PCSK9 inhibitor therapy
- Familial hypobetalipoproteinaemia (genetic — very rare)
- Severe malnutrition
- Hyperthyroidism
- Familial hypercholesterolaemia (FH) — genetic LDL receptor dysfunction
- Unhealthy diet (saturated and trans fats)
- Sedentary lifestyle and obesity
- Hypothyroidism
- Type 2 diabetes and insulin resistance
- Nephrotic syndrome
- Medications: corticosteroids, immunosuppressants, some retinoids
FAQs
Target LDL depends on your cardiovascular risk level: for the general healthy adult, < 3.0 mmol/L is the NICE primary prevention target. For people with existing cardiovascular disease (post-heart attack, stroke, or peripheral artery disease), the ESC recommends 50% reduction from baseline. Emerging evidence suggests that lower LDL is better throughout life — there appears to be no lower threshold for benefit.
Mild muscle aches (myalgia) occur in 5–10% of statin users but are often related to the nocebo effect (expectation of side effects). True statin-induced myopathy (muscle inflammation with raised CK) is rare (< 0.1%) and myopathy progressing to rhabdomyolysis (muscle breakdown) is very rare. Coenzyme Q10 levels are reduced by statins and some patients find supplementation helps with muscle symptoms. If muscle symptoms are severe, discuss alternative statins or non-statin therapies (ezetimibe, PCSK9 inhibitors) with your doctor.
Yes. Small dense LDL (sdLDL) particles are more atherogenic than larger, more buoyant LDL particles: they penetrate the arterial wall more easily, are more susceptible to oxidation, and have lower binding affinity for LDL receptors (so they circulate longer). sdLDL is increased in insulin resistance, metabolic syndrome, and hypertriglyceridaemia. ApoB measurement captures both large and small LDL particles and better reflects true atherogenic particle burden.
Diet and lifestyle can reduce LDL by 10–30%. Effective strategies: replace saturated fats with unsaturated fats; eat 10–25g of soluble fibre daily (oats, psyllium, legumes); consume plant sterols (2g/day in fortified foods); lose excess weight; increase aerobic exercise. For LDL > 5.0 mmol/L or with significant cardiovascular risk, medication (statins) is usually needed in addition to lifestyle changes to achieve target levels.
PCSK9 is a liver enzyme that degrades LDL receptors — reducing the liver’s ability to clear LDL from the blood. People with gain-of-function PCSK9 mutations have very high LDL and early heart disease. PCSK9 inhibitor drugs (evolocumab, alirocumab) block this enzyme, dramatically increasing LDL receptor availability and lowering LDL by 50–65% on top of statin therapy. They are used for familial hypercholesterolaemia and very high-risk patients who cannot achieve adequate LDL reduction with statins alone.
References
- Ference BA, et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease. Eur Heart J. 2017;38(32):2459–2472. View source
- NICE. Cardiovascular disease: risk assessment and reduction, including lipid modification. CG181. Updated 2023. View source
- Cholesterol Treatment Trialists Collaboration. Efficacy and safety of more intensive lowering of LDL cholesterol: a meta-analysis of data from 170,000 participants in 26 randomised trials. Lancet. 2010;376(9753):1670–1681. View source