Kolesteroliin

Kolesteroliin is a sterol lipid essential to many animals. It is a major component of animal cell membranes, where it modulates fluidity and the formation of lipid rafts, and it serves as a biochemical precursor for bile acids and steroid hormones, including cortisol, testosterone, estrogen, and aldosterone, as well as vitamin D.

Chemically, kolesteroliin has a rigid four-ring steroid structure with a hydroxyl group. In cells it exists in free form or as cholesterol esters stored in lipid droplets; transport in the bloodstream occurs mainly within lipoproteins, because free kolesteroliin is insoluble in water. Dietary cholesterol is absorbed in the intestine and packaged into chylomicrons, while endogenous cholesterol is produced mainly by the liver and distributed via VLDL; HDL is involved in reverse transport.

Mevalonate pathway in the liver synthesizes kolesteroliin; HMG-CoA reductase is the rate-limiting step and is regulated by cellular sterol levels. Bile acids derived from kolesteroliin are secreted into the intestine and reabsorbed (enterohepatic circulation).

Health aspects: high levels of low-density lipoprotein cholesterol (LDL-C) and low levels of high-density lipoprotein cholesterol (HDL-C) are associated with a higher risk of atherosclerotic cardiovascular disease. Management includes lifestyle changes and, when needed, drugs such as statins or ezetimibe. Dietary guidance emphasizes limiting saturated fats and trans fats, and increasing intake of soluble fiber and plant sterols that reduce absorption.