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How can high cholesterol levels lead to narrowed blood vessels, heart attacks, and strokes?

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A composite diagram shows the structural formulas, space-filling models, and simplified depictions of lipid molecules including stearic acid and phosphatidylcholine, and how these assemble into a micelle and lipid bilayer, with labels identifying hydrophilic heads and hydrophobic tails. — Lipid Structure and properties of two representative lipids. Both stearic acid (a fatty acid) and phosphatidylcholine (a phospholipid) are composed of chemical groups that form polar “heads” and nonpolar “tails.” The polar heads are hydrophilic, or soluble in water, whereas the nonpolar tails are hydrophobic, or insoluble in water. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.

High cholesterol levels contribute to the development of atherosclerosis, a chronic condition where fatty substances accumulate in the inner walls of arteries.12

The Process of Vessel Narrowing

Cholesterol is insoluble in blood and must be transported by lipoproteins, primarily low-density lipoproteins (LDLs). When blood cholesterol is high, LDLs infiltrate the endothelium of the arterial wall. Immune cells called macrophages ingest these lipids, becoming "foam cells" that die and accumulate within the lining. Over time, this buildup—along with calcium, smooth muscle cells, and cellular debris—forms atherosclerotic plaques. These plaques thicken and harden, narrowing the arterial channel and restricting oxygen-rich blood flow to vital organs.213

Heart Attacks and Strokes

The danger of these plaques extends beyond simple narrowing:
* Heart Attacks: When plaques obstruct the coronary arteries, they can reduce blood supply to the heart muscle, causing angina pectoris. If a plaque ruptures, it triggers the formation of a blood clot (thrombus), which can completely block blood flow, leading to a heart attack.143
* Strokes: Similar plaque buildup or resulting clots in the cerebral vessels can obstruct blood supply to the brain, causing a stroke.13