β-Sitosterol is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. Sitosterols are white, waxy powders with a characteristic odor. They are hydrophobic and soluble in alcohols.
It is widely distributed in the plant kingdom and found in Nigella sativa, pecans, Serenoa repens (saw palmetto), avocados, Curcurbita pepo (pumpkin seed), Pygeum africanum, cashew fruit, rice bran, wheat germ, corn oils, soybeans, sea-buckthorn, wolfberries, and Wrightia tinctoria.
Alone and in combination with similar phytosterols, β-sitosterol reduces blood levels of cholesterol, and is sometimes used in treating hypercholesterolemia. β-Sitosterol inhibits cholesterol absorption in the intestine. When the sterol is absorbed in the intestine, it is transported by lipoproteins and incorporated into the cellular membrane. Phytosterols and phytostanols both inhibit the uptake of dietary and biliary cholesterol, decreasing the levels of LDL and serum total cholesterol. Because the structure of β-sitosterol is very similar to that of cholesterol, β-sitosterol takes the place of dietary and biliary cholesterol in micelles produced in the intestinal lumen. This causes less cholesterol absorption in the body.