What does cholesterol actually do, and what do the numbers mean?
Cholesterol is a lipid the body needs — a component of every cell membrane and the raw material for steroid hormones, vitamin D and bile acids. Your body makes most of it. The problem is not its existence but how it is transported and where it ends up.
Why lipoproteins matter. Cholesterol does not dissolve in blood, so it travels wrapped in particles. The particle determines the effect, which is why "good" and "bad" cholesterol are the same molecule in different vehicles.
LDL carries cholesterol to tissues. LDL particles can enter the artery wall, where they are retained and oxidised, triggering an inflammatory response that builds plaque. The causal role of LDL in cardiovascular disease is among the best-established findings in medicine, supported by genetic, epidemiological and trial evidence.
HDL carries cholesterol back to the liver. Higher HDL is associated with lower risk — but trials raising HDL with drugs have not reduced events, which strongly suggests it is a marker rather than a lever. This is an important correction to older advice.
Triglycerides are a different lipid, associated with risk and strongly affected by alcohol, refined carbohydrate and weight.
What a result contains: total cholesterol, LDL, HDL, non-HDL cholesterol, triglycerides, and sometimes apolipoprotein B or lipoprotein(a).
Non-HDL cholesterol — total minus HDL — is now often preferred, because it captures all the atherogenic particles and does not require fasting.
Lipoprotein(a) is largely genetically determined, is not affected by lifestyle, and is worth measuring once, because a high level changes risk assessment and is invisible on a standard panel.
Why a target number is the wrong question. Treatment decisions are based on overall cardiovascular risk — age, sex, blood pressure, smoking, diabetes, family history and lipids together — not on a cholesterol figure alone. The same LDL means different things in different people.
What lowers LDL: dietary change with emphasis on replacing saturated fat, soluble fibre, weight and activity, and statins or other drugs where risk warrants.
General information, not medical advice.