The endothelium is the single-cell layer lining every blood vessel. Endothelial function is its capacity to vasodilate appropriately in response to demand — primarily via nitric oxide signaling.
Mechanism — Endothelial dysfunction precedes plaque formation by years to decades. Driven by oxidative stress, inflammation, hyperglycemia, hypertension, and aging. Reverses early with lifestyle change; reverses less easily once established.
Use case — Test via flow-mediated dilation (research) or peripheral arterial tonometry (EndoPAT). Support via Zone 2 cardio, beetroot, L-citrulline, polyphenols, and risk-factor management.
Caveats — Clinical testing isn't widely available. The right move is to treat the upstream risk factors — glucose, lipids, blood pressure, inflammation — and the endothelium follows.