The activity and absorption relationship of cholesterol and phytosterols

Cholesterol is an essential lipid for mammalian life, but a high cholesterol level can almost guarantee the eventual onset of vascular diseases and, in some cases, can lead to death. It has been shown that there is a direct connection between hi-h cholesterol levels and vascular diseases. Some methods for lowering the serum cholesterol level, thereby preventing the development of these diseases, have been developed and those include drugs and food additives. Since both drugs and food additives act to inhibit the uptake of cholesterol. understanding the sterol absorption process is the key to understanding exactly how drugs and food additives reduce serum cholesterol levels. The major drawback of using anti-cholesterol drugs is related to their side effects, and therefore, natural food additives called plant sterols (phytosterols) have been developed as an attractive alternative. Phytosterols are sterols that are synthesized only in plants and that are structurally similar to cholesterol but with the inclusion of art extra hydrophobic carbon chain at the C-24 position. Phytosterols and their esters reduce cholesterol level in the blood in spite of the fact that they are poorly absorbed into the blood stream. The mechanism by which phytosterols/phytosterol esters interfere with cholesterol absorption is not completely clear, but based on the present understanding, three distinct features have been recognized: (1) physico-chemical effects (e.g. competitive solubilization and co-crystallization); (2) effects at the absorption site (e.g. hydrolysis by lipases and esterases); (3) effects on intracellular trafficking of sterols. Due to phytosterols' poor solubilization in oil and water, they must be taken in high doses to achieve a reduction in cholesterol level. One of the goals of the food and pharmaceutical industries, therefore, is to develop products that effectuate the same decrease in cholesterol level but in smaller sterol doses achieved by increasing sterol bioavailability. The first line of products to meet the increased bioavailability criterion was the oil-soluble esterified phytosterols combined with fatty acids, which exhibit solubility in oil 10 times higher than that of pure phytosterols. The three primary methods of phytosterol inclusion in food are suspension, precipitation and microemulsion. (c) 2005 Elsevier B.V. All rights reserved.