Stérols

Stérols, or sterols, are a subgroup of steroids characterized by a hydroxyl group at the C3 position of a tetracyclic ring system and a hydrophobic side chain. They occur in all eukaryotic kingdoms and function as membrane components and as biosynthetic precursors for bile acids and steroid hormones.

In animals, the predominant sterol is cholesterol; in plants, major sterols include sitosterol, campesterol and stigmasterol; fungi synthesize ergosterol. Other sterol intermediates such as lanosterol and desmosterol participate in biosynthetic pathways leading to cholesterol and other sterols.

Sterols play structural roles in membranes, helping to regulate fluidity and permeability and supporting the organization of membrane microdomains. They also serve as precursors for bile acids, steroid hormones and certain signaling molecules. Biosynthesis occurs via the mevalonate pathway; animals synthesize cholesterol endogenously and obtain sterols from the diet, with plants producing phytosterols.

Dietary plant sterols (phytosterols) and their saturated forms (stanols) can reduce intestinal absorption of cholesterol, contributing to lower low-density lipoprotein cholesterol in some individuals. Plant sterols are widely used in fortified foods and supplements at total daily intakes around 1–2 grams. People with sitosterolemia or other rare sterol metabolism disorders should avoid high sterol intake, and high amounts may interfere with absorption of fat-soluble vitamins.