One fact anchors this whole guide, and it's about as settled as anything in medicine: the ApoB-carrying particles (LDL and its relatives) don't merely correlate with heart disease — they cause it, in proportion to how many there are and for how long you carry them. That's why 'how low, how early' is the entire game.
Every atherogenic particle — LDL, VLDL, IDL, remnants, and Lp(a) — carries exactly one ApoB molecule. So an ApoB level is a direct count of the particles that lodge in the artery wall. LDL-cholesterol measures the cholesterol cargo inside those particles, which varies; ApoB counts the trucks. Atherosclerosis tracks the trucks — which is why ApoB is the more accurate number (test section).
Causality rests on three lines that all give the same log-linear, dose-dependent answer. Genetics (Mendelian randomisation): 50+ different LDL-lowering gene variants each lower heart disease by the same amount per unit of LDL — whatever the mechanism — the fingerprint of a causal agent. Trials (CTT meta-analyses): each 1 mmol/L (~39 mg/dL) lower LDL cuts major vascular events ~22%, with benefit continuing safely to very low levels and no threshold. Epidemiology: a strong graded association across ~2 million people. The European consensus verdict: LDL causes atherosclerotic cardiovascular disease. Evidence ●●●●●
Arterial damage is a function of particle concentration times duration — think 'cholesterol-years', like pack-years for smoking. That's why lifelong genetically lower LDL cuts heart disease roughly three times more per unit than the same reduction started in middle age. The practical corollary is lower and earlier: the area under the curve over decades is what builds plaque.
This exact claim — that ApoB/LDL causes disease rather than just marking it — is the precise point a minority of statin skeptics dispute. It's a real debate about the evidence and it's handled fairly in the statins section; the mainstream position, backed by the Mendelian-randomisation data above, is that causality is settled.
ApoB is the number to know
If you take one idea from this guide, it's that lowering the number of ApoB particles is the lever that stops and reverses plaque. Everything downstream — statins, ezetimibe, PCSK9 drugs, diet — is judged by how much it lowers that particle burden and for how long.
The Cholesterol Guide