Cholesterol is well known for its connection with coronary artery disease, but it has an important role in the health and function of the body as well. Cholesterol is present in every cell of the body and is an integral part of cell membranes, the brain and nerves. It is responsible for structural support of the cells and is important in producing the bile that helps digest fats. It is needed to produce the sex hormones estrogen and testosterone. Without cholesterol, the body could not produce Vitamin D. But too much cholesterol in the blood raises the risk of heart disease. Cholesterol levels can be lowered by diet, exercise and medication.
Cholesterol Components
Total cholesterol includes high density lipoprotein (HDL), low density lipoprotein (LDL) and triglycerides. The HDL and LDL lipoproteins transport fatty materials through the watery bloodstream. Triglycerides are the chief form of fat in the diet and the main storage form of fat in the body.
Sources of Cholesterol
Dietary cholesterol comes from animal sources, such as meat, eggs, milk, butter and cheese. The diet of most people contains more than enough cholesterol to meet the body's needs. The effect of dietary cholesterol on blood levels of cholesterol is influenced by genetic tendencies. The main dietary cause of high cholesterol is saturated fat also found in animal sources, including beef, veal, lamb, pork, poultry, butter, milk and cheese. Some plant sources of saturated fat are coconut and tropical oils, such as palm oil.
The body does not need dietary cholesterol or saturated fat, however, because the liver is capable of making more than enough cholesterol to meet the body's needs. So the body must regulate how much cholesterol it makes according to its needs, lifestyle factors including diet, smoking, lack of exercise, obesity and caffeine as well as genetic influences.
Cholesterol in Cell Membranes
Every cell of the body needs cholesterol to maintain the integrity of its cell membrane. Cholesterol makes the cell membrane more rigid but prevents it from crystallizing. A cell membrane is made of phospholipids lined up in an orderly bilayer with fatty acid "tails" pointing away from the surrounding watery fluid and glycerol and phosphate "heads" pointing toward the watery fluid. Cholesterol's structure with a very small head group and a bulky tail group and rigid steroid ring causes a bending that immobilizes nearby phospholipids and thus makes the membrane somewhat less fluid. This helps maintain the structure and supports the purpose of the cell membrane.
Cholesterol and Bile
Cholesterol is needed for the liver to make bile, a greenish fluid that is stored in the gallbladder and used in the intestine to digest foods that contain fat. Bile emulsifies or breaks down large globules of fat so enzymes that digest fat can mix better with the smaller globules. Bile in the intestine helps absorb cholesterol and the fat-soluble Vitamins A, D, E and K from food. From the intestine, cholesterol is released back into the bloodstream. Part of it is recycled to the liver and part is excreted as waste from the colon.
Cholesterol and Hormones
Cholesterol is the precursor for steroidal hormones. Cholesterol is used to produce the sex hormones estrogen and testosterone that trigger development of physical traits of women and men and play a role in reproduction. Cortisol which is involved in the immune system and in regulation of blood sugar is mainly synthesized from cholesterol. Cholesterol may be a limiting factor in the synthesis of aldosterone which helps retain water and salt in the body.
Cholesterol and Vitamin D
In the presence of sunlight, the body can use the photolytic action of ultraviolet light on the cholesterol in the skin cells to make Vitamin D. Vitamin D is needed to maintain the balance of calcium and phosphorus for strong bones and teeth.
References
- "Nutrition Through the Life Cycle, Third Edition;" Judith E. Brown (2008)
- Cholesterol in the human body
