Plant sterols, cholesterol precursors and oxysterols: Minute concentrations—Major physiological effects

•Plant sterols, cholesterol precursors, and oxysterols are present at low concentrations in circulation and tissues.•Small amounts of plant sterols enter the circulation and can be used as biomarkers for sterol absorption.•Cholesterol precursors are employed as measures of cholesterol synthesis and in the diagnostics of certain diseases.•Oxysterols arising through enzymatic processes regulate lipid metabolism and inflammation/immunity•Oxysterols of non-enzymatic origin reflect oxidative stress but can also be employed to diagnose rare inherited diseases. Non-cholesterol sterols are present in our body at very low concentrations as compared to cholesterol. Small changes in the structure of sterol molecules confer them highly distinct biological activities. The best-known example are steroid hormones derived from cholesterol. During the past decade, our knowledge of also other biomolecules related to or derived from cholesterol, particularly plant sterols, biosynthetic precursors of cholesterol, and oxysterols, has expanded rapidly. In this review article we recapitulate the latest insights into the properties and physiological activities of these non-cholesterol sterols, as well as their importance in disease processes and potential as diagnostic biomarkers.