Before considering the details of how the body structures cholesterol production and LDL distribution, it is crucial to differentiate between the two. There is a common misconception that cholesterol consists of two sorts: one bad, called LDL, and the other good, called HDL. However, LDL and HDL are actually types of lipoproteins that transport cholesterol.
Cholesterol
Cholesterol's importance cannot be overstated. It is the substrate of structure to every cell membrane, and when cells combine to form tissue, cholesterol is the framework holding them together. It also facilitates cell division, and it is essential to cell growth. At the most fundamental level, without cholesterol, life could not exist. Nevertheless, cell maintenance is not the extent of cholesterol's reach. It regulates several metabolic functions including tissue metabolism, and hormones supply. It also aids the absorption of fat-soluble vitamins, and controls the balance of minerals, and present research indicates more is still to come. In October 2005 Harvard Medical School published in its online edition of "Focus" a study in which researchers observed immune system functions relating to cholesterol distribution. According to the researchers, the prior belief that viewed heart disease as a result from abnormal blood level lipid distribution, may in fact be the result of lipid mis-distribution to the immune system.
Lipoproteins
There are five recognized categories of lipoproteins. They are specialized transport proteins that serve to shuttle insoluble lipids through the water-based bloodstream. A lipoprotein is a submarine-like particle with an outer shells that works well in solution with blood, and it has an inner chamber fit to house fats and cholesterol in route to cells. Some lipoproteins transport fats to tissues, others take them to the liver, and some take them from the liver and deliver them to cells.
Low Density Lipoprotein
Low-density lipoprotein, or LDL, is the primary shuttle that transports cholesterol and delivers it to every cell in the body. Since cholesterol has a fundamental role in the maintenance of cell membranes, increases in its transport to cells that have suffered damage would appear to make sense. According to researchers at the University of Virginia, LDL, in connection with atherosclerosis, is greater both in levels of circulation in the blood, and in retention at damaged arterial sites. Such an accumulation of LDL, however, impairs cholesterol's exit from the LDL particle; consequently, the cholesterol cannot enter the cell to make the needed repairs.
Reevaluating Health Implications
For decades, the association between blood cholesterol levels and heart disease was thought to have a causative relation, but the vast amounts research have generally acknowledged that the cause of heart disease is difficult to know. According to a 2005 article in "Current Pharmaceutical Design," much of the current research focuses on understanding the mechanisms of cholesterol's LDL distribution and how these may contribute to LDL accumulation and death. Given the vital role of cholesterol in cellular maintenance, and the research on its role in the immune response, it may be reasonable to consider that an elevation in its production is an indication, rather than a cause, for why a disease exists.
References
- "Current Pharmaceutical Design"; Macrophage Differentiation to Foam Cells; Pavel Shashkin, et al.; 2005
- Harvard Medical School: Focus: Special Delivery Brings Fats to Immune System:
- "Fundamentals of Anatomy & Physiology 8th Edition"; Frederic Martini, Pearson Education; 2009
