LDL Cholesterol

What is LDL-C?

Cholesterol does not dissolve in blood, so it travels inside lipoprotein particles. LDL-C is the mass of cholesterol carried by the low-density ones. Importantly, it measures cargo, not vehicles: two people with the same LDL-C can be carrying very different numbers of particles, which is why apolipoprotein B is sometimes measured alongside it.

What is LDL-C made of, and where does it come from?

Each LDL particle carries exactly one molecule of apolipoprotein B-100 wrapped around a core of cholesteryl esters and triglycerides, with a surface shell of phospholipids and free cholesterol. The 'one apoB per particle' rule is what makes apoB a direct particle count.

What does LDL-C do in the body?

LDL particles deliver cholesterol to tissues that need it for cell membranes and for making steroid hormones and bile acids. The liver clears them from circulation through LDL receptors, whose recycling is regulated by PCSK9 — the target of a whole drug class. Atherosclerosis begins when apoB-containing particles cross the arterial lining and are retained there; the longer the exposure and the higher the concentration, the more plaque accumulates.

What does a high LDL-C mean?

Higher LDL-C means more cholesterol-carrying particles available to enter the artery wall, and a correspondingly higher lifetime risk of heart attack and stroke. The effect is cumulative — it is concentration multiplied by years of exposure that matters, which is why a moderately raised value at 30 is not a small thing. What counts as a target is not universal: it depends on overall cardiovascular risk, and is set with a clinician rather than read off a lab range.

Common causes:

• Dietary pattern high in saturated fat and, in some people, in dietary cholesterol.
• Familial hypercholesterolaemia — an inherited receptor defect. Worth considering when LDL-C is very high, when it is high from a young age, or when heart disease runs early in the family.
• Untreated hypothyroidism, which reduces LDL receptor activity and is a genuinely reversible cause.
• Nephrotic syndrome, cholestatic liver disease, and some medications including corticosteroids and certain immunosuppressants.
• Weight gain and insulin resistance, which typically raise triglycerides and shift LDL toward smaller, denser particles.

What does a low LDL-C mean?

Low LDL-C is generally favourable, and no threshold has been found below which lowering it with medication stops being beneficial. A low value that was not the result of treatment or diet is worth a second look, since it can accompany hyperthyroidism, malnutrition, malabsorption, advanced liver disease, or an inherited lipoprotein disorder.

Common causes:

• Lipid-lowering treatment working as intended.
• Hyperthyroidism.
• Malnutrition, malabsorption, or advanced liver disease.
• Acute severe illness or the weeks following a heart attack.

What moves LDL-C apart from disease?

How LDL-C was obtained — calculated or measured directly either direction

Most laboratories calculate LDL-C from other lipids using the Friedewald equation, which becomes unreliable when triglycerides are high (above roughly 4.5 mmol/L) and tends to underestimate at low LDL-C. If your value looks inconsistent with the rest of the panel, check which method the report used.

Recent acute illness, surgery or heart attack lowers it

LDL-C falls for several weeks afterwards and can read deceptively normal. A value drawn during or just after an acute event does not represent the usual level.

Thyroid status either direction

An underactive thyroid raises LDL-C and an overactive one lowers it. Thyroid function is usually checked before treating a newly found elevation.

Pregnancy raises it

Lipids rise substantially and physiologically through pregnancy. Screening results from this period are not comparable with baseline.

Fasting either direction

Non-fasting samples are acceptable for routine screening under current European guidance. Fasting matters mainly when triglycerides are high, because that is when the calculation degrades.

Weight change either direction

Losing weight tends to lower LDL-C modestly; the larger effects of weight loss usually show up in triglycerides and HDL-C.

Which other tests are read together with LDL-C?

Apolipoprotein B read as a ratio

ApoB counts the particles rather than the cholesterol they carry. When LDL-C and apoB disagree — common with high triglycerides or diabetes — apoB is the better predictor of risk.

Total Cholesterol same panel

Total cholesterol is the sum across all lipoproteins; subtracting HDL-C from it gives non-HDL-C, which captures every atherogenic particle in one number.

Triglycerides can distort it

High triglycerides break the Friedewald calculation and shift LDL toward smaller, denser and more atherogenic particles — so the same LDL-C carries more risk.

HDL Cholesterol same panel

Reported together on every lipid panel and needed to derive non-HDL-C. Note that raising HDL-C with drugs has not reduced events, so it is read as a risk marker rather than a treatment target.

Thyroid Stimulating Hormone can distort it

An underactive thyroid is a reversible cause of raised LDL-C and is usually excluded before starting lipid-lowering treatment.

Which foods affect LDL-C?

• Replacing saturated fat with unsaturated fat — olive oil, nuts, oily fish instead of butter, fatty meat and palm oil — lowers strong evidence
• Soluble fibre — oats and barley beta-glucan, legumes, psyllium — lowers strong evidence
• Foods fortified with plant sterols or stanols — lowers strong evidence
• A daily handful of tree nuts — lowers moderate evidence
• Industrial trans fats — raises strong evidence

Which supplements are studied for LDL-C?

Plant sterols / stanols strong evidence

Compete with cholesterol for absorption in the intestine. Around 2 g a day lowers LDL-C by roughly 8-10%, and the effect adds to that of statins.
Typical dose: 2 g/day, taken with meals
Cautions: Not suitable for people with sitosterolaemia, a rare inherited disorder of sterol absorption. Slightly reduces absorption of carotenoids; eating plenty of vegetables offsets this.

Psyllium (soluble fibre) moderate evidence

Binds bile acids in the gut, forcing the liver to draw on circulating cholesterol to make more. Expect a modest reduction, in the region of 5-7%.
Typical dose: 5-10 g/day
Cautions: Increase the dose gradually and take with plenty of water; abrupt introduction commonly causes bloating. Separate from other medications by at least two hours, as it can reduce their absorption.

Red yeast rice moderate evidence

Contains monacolin K, which is chemically identical to the drug lovastatin. It lowers LDL-C for exactly the reason a statin does.
Typical dose: no general dose given
Cautions: This is a statin sold as a supplement. It carries the same risks — muscle injury and liver enzyme rises — without prescription oversight. Monacolin content varies widely and unpredictably between products, so the effective dose is unknown. Do not combine with a prescribed statin, and do not use during pregnancy or breastfeeding. Discuss with a doctor first.

How does exercise affect LDL-C?

Regular aerobic exercise moderate evidence

How much: At least 150 minutes a week at moderate intensity, or 75 minutes vigorous.
What to expect: The direct effect on LDL-C is small. Exercise earns its place here through triglycerides, HDL-C, blood pressure, insulin sensitivity and overall cardiovascular risk — do not judge it by this number alone.

Resistance training moderate evidence

How much: Two or three sessions a week.
What to expect: Small additional reduction in LDL-C, and it preserves lean mass during weight loss — which is when lipid improvements are largest.

Which lifestyle factors affect LDL-C?

Stopping smoking strong evidence

Smoking barely moves LDL-C but sharply increases the damage those particles do, by oxidising them and injuring the artery lining. On cardiovascular risk it outweighs almost any dietary change.

Knowing your family history strong evidence

A parent or sibling with heart disease before 55 (men) or 65 (women), or persistently very high LDL-C, should prompt a conversation about familial hypercholesterolaemia. It is common, treatable, and usually diagnosed decades later than it could be.

How should you prepare for a LDL-C test?

• Fasting is not required for routine screening; fast if triglycerides are known to be high or the clinician asks.
• Do not test during or in the weeks after an acute illness, surgery or heart attack — the value will read low.
• Check whether the report says the LDL-C was calculated or directly measured, especially when triglycerides are high.
• Compare like with like over time: the same laboratory and the same method, since between-method differences can exceed real change.

References

1. Ference BA et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease — EAS Consensus Panel. Eur Heart J 2017 — https://doi.org/10.1093/eurheartj/ehx144
2. Mach F et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias. Eur Heart J 2020 — https://doi.org/10.1093/eurheartj/ehz455
3. Gylling H et al. Plant sterols and plant stanols in the management of dyslipidaemia — EAS Consensus Panel. Atherosclerosis 2014 — https://doi.org/10.1016/j.atherosclerosis.2013.11.043