Cholesterol has a bad reputation in popular culture, but in fact it's an important biomolecule that's essential to life. Humans need cholesterol as a starting material for synthesizing several different molecules, and also use it to help regulate the fluidity of the cell membrane. Too much cholesterol in the body, however, can be harmful.
Cholesterol Chemistry
Cholesterol is a biomolecule that falls into the class of lipids, which are molecules with low water-solubility. Other lipids include nutritional fats, or triglycerides, and the fats that make up cell membranes, called phospholipids. Humans can obtain cholesterol from the diet, either directly or indirectly. You can synthesize cholesterol from some sources of fat, and some foods contain preformed cholesterol. Your cells also can make cholesterol from a variety of smaller molecules.
Molecules Made From Cholesterol
Your body needs cholesterol to make many different things, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." First, when you expose your skin to sun, the sunlight turns cholesterol in the skin into vitamin D, which you use to take up calcium from your food. Additionally, you make steroid hormones -- including the sex hormones estrogen, progesterone and testosterone -- from cholesterol.
Cholesterol and Membranes
Another important biological use of cholesterol is to help regulate the stiffness of the cell membranes. Your cells are surrounded by membranes that, to function properly, must hold together without becoming stiff. Cholesterol helps hold the membranes together and keeps them from being too fluid, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry." If you have too little cholesterol in your cell membranes, they'll fall apart. With too much cholesterol, they'll become too stiff and the cells will rupture.
Too Much Cholesterol
Since cells can't afford to have too much cholesterol in their membranes, they don't take up cholesterol from the blood unless they need it. As a result, explains Dr. Lauralee Sherwood in her book "Human Physiology," if you eat a diet high in cholesterol or certain kinds of fat, you'll end up with too much cholesterol in the bloodstream because cells will have plenty and will stop taking it up. This can lead to the formation of arterial plaques, which cause heart disease.
Cholesterol and Fat
The fats most associated with the formation of cholesterol and buildup of cholesterol in the bloodstream are saturated and trans fats. Saturated fats occur mostly in animal sources, though certain tropical plants also contain them. Trans fats occur in processed and fast foods, but don't occur to any significant extent in nature. When you consume large quantities of saturated and trans fats, your blood cholesterol levels become quite high, as cells have all the cholesterol they need. This leads to heart disease.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
