Sterols, also known as steroid alcohols, are a class of chemicals that play multiple important roles in the body. They have parts that can dissolve in fat like molecules and parts that can dissolve in water. The most widely known human sterol is cholesterol, which serves as a precursor to steroid hormones and fat-soluble vitamins. Plant sterols are found in plants and taken as supplements by some people. A healthcare professional should be consulted regarding dietary and healthcare decisions.
Cell Signalling
Cell signalling refers to the ability of the cell to effectively communicate. Cellular communication is important, because cells in any given organ or tissue work together, and cells often need to signal distant organs as well. Sterols play a vital role in cell signalling in several ways. They help regulate the process of development. In addition, they pass on messages received from outside the cell to effect changes inside the cell. In this capacity they are known as "second messengers." Finally, they act as steroid hormones, which are molecules that are synthesized by hormonal organs to signal distant organs. Some of the more common steroid hormones are cortisol, aldosterone, testosterone and estrogen. Cortisol is a stress hormone, aldosterone regulates mineral balance in the body, and testosterone and estrogen are male and female sex hormones.
Fat-soluble Vitamins
Fat-soluble vitamins are synthesized by other organisms from sterols and then passed on to people in the diet. They include vitamins A, D, E and K. Vitamin A is important for eye and skin health. Vitamin D has many functions, including helping the immune system and strengthening bones. Vitamin E is an antioxidant that helps protect against cellular damage. Vitamin K is important for blood clotting.
Membrane Stability
Sterols, particularly cholesterol, are integral to the stability of the cell membrane. The membrane is the outer covering of the cell, analogous to the skin. Chemically, it is called a lipid bilayer. Lipids refer to fat-like molecules that function to keep the environments inside and outside the cell separate. Bilayer refers to the fact that there are two layers. The cholesterol embedded in the membrane maintains flexibility, or fluidity, and hence stability to the membrane over a range of temperatures.
Phytosterols
Phytosterols are found in plants and are ingested when plant foods are eaten. Some people take concentrations of plant sterols. A 2003 study in the "American Journal of Clinical Nutrition" showed that sterols may interfere with the absorption of excess cholesterol from the diet and therefore may be good for the heart and blood vessels. However, the long-term effects and side effects still need to be established.
References
- "Lehninger Principles of Biochemistry, 4th Ed."; David L. Nelson and Michael M. Cox; 2004
- "Harrison's Principles of Internal Medicine, 17th Ed."; Anthony S. Fauci, et al; 2008
- "American Journal of Clinical Nutrition"; Inhibition of Cholesterol Absorption by Phytosterol-replete Wheat Germ Compared with Phytosterol-depleted Wheat Germ; RE Ostlund Jr, et al; June 2003
