Cholesterol – The Good and Bad
Cholesterol is the principal sterol for animals and humans alike, consisting of a hydroxyl group, a steroid group, and a hydrocarbon side chain. (htpp://EncyclopediaBritannica.com). It is an insoluble lipid substance produced by the liver and found both in cell membranes and circulating in the blood stream.
The name cholesterol is derived from the Greek word chole, which means bile, in conjunction with stereos, also a Greek word that means solid. That is because it was discovered in the 18th century in solid form, as gallstones, by François Poulletier de la Salle in 1769. The -ol part in the word is the way alcohol is named in chemistry. A few years later the chemist Eugène Chevreul gave it the name “cholesterine”. (htpp://EncyclopediaBritannica.com).
Cholesterol was correctly synthesized for the first time in 1951 by Robert B. Woodward, an American chemist and Nobel Prize winner, and it has been known to have potentially dangerous health effects as early as the year 1910 (http://science.jrank.org/pages/1454/Cholesterol-History.html) On that year, Russian biologist Nikolai Antischow found plaques of cholesterol on the arterial walls of laboratory rabbits fed a high cholesterol diet. This breakthrough discovery prompted scientists around the world to further study the controversial and elusive role of cholesterol and its relation to heart disease, currently the leader in deaths for both men and women in the Western world.
That’s because even though cholesterol is involved in many important metabolic processes, there has been increasingly clear evidence that when present in elevated levels it can lead to Cardiovascular Disease (CVD), stroke, and atherosclerosis.
Cholesterol, contrary to its popular image as a potent enemy of
health and longevity, is actually a crucial substance that performs
innumerable vital functions in the body. Cholesterol is needed for
the synthesis of bile acids, which are essential for the absorption of
fats, and of many hormones such as testosterone, estrogen,
dihydroepiandrosterone, progesterone, and cortisol. Together with
sun exposure, cholesterol is required to produce vitamin D.
Cholesterol is an essential element of cell membranes, where it
provides structural support and may even serve as a protective
antioxidant. (Colpo 83)
Cholesterol levels are measured in milligrams per deciliter of blood. The desirable levels are 200 mg/dL, while anything over 239 mg/dL is considered high.
The imminent connection between CVD and elevated levels of blood cholesterol is that as excessive amounts circulate freely in the blood stream, it accumulates in the arterial walls. When this process continues over the years, the buildup, also called plaque, hardens and therefore narrows the arteries. Calpo mentions that:
The plaques are complex entities with numerous
components, including smooth muscle cells, calcium,
connective tissue, white blood cells, cholesterol,
and fatty acids (84).
The result is a reduced volume of blood reaching the heart; blood that is rich in oxygen necessary for its normal function. A heart attack occurs when an artery gets completely blocked.
Of particular importance is the Framingham Heart Study started in 1948 under the direction of the National Heart, Lung, and Blood Institute and the University of Boston. Culminating in 2005 and spanning three generations of thousands of people, it conclusively catalogs hypercholesterolemia as a risk for CVD and other serious health conditions. This study spawned over 1,200 medical research articles published in leading medical journals (Byrne).
Still under investigation by the Framingham Heart Study is the direct relationship of low density lipoproteins (LDL), commonly known as “bad cholesterol” and CVD (http://www.framingham.com/heart/). There is mounting evidence that low density lipoproteins (LDL) and high density
lipoproteins (HDL) play an important role in the overall health effects of cholesterol:
Because cholesterol is water-insoluble, it must be transported
inside lipoproteins. Various types of lipoproteins exist, but the two
most abundant are low-density lipoprotein (LDL) and high-density
lipoprotein (HDL). The main function of LDL is to transport
cholesterol from the liver to tissues that incorporate it into cell
membranes. HDL carries old cholesterol that has been discarded
by cells back to the liver for recycling or excretion.(Colpo 83)
Based on this information, HDL is considered a benign type of cholesterol, while LDL is feared as the main culprit of increasing the incidence of a large variety of cardiovascular ailments. Optimal LDL levels are 100 mg/dL, and anything over 159 mg/dL is considered high, placing the patient at risk of CVD. On the other hand, because HDL is a type of cholesterol that could prevent heart disease, the higher its levels the better for the patient. Thus, doctors look for numbers at around 60 mg/dL, while blood test results lower than 40 mg/dL might place the patient at an elevated risk of heart disease.
Furthermore, there is clear evidence that genetics plays a role in hypercholesterolemia:
The cells of the body contain information, in the form of genes, for
the body to make all the necessary structural components and
chemicals to ensure normal function. Genes contain the
instructions for the way in which cholesterol and other fats are
taken into the cells. The LDLR gene contains the instructions for
the body to make the low-density lipoprotein (LDL) “receptor”
(R) that enables the absorption of the LDL into the cell. When this receptor
is not working properly, cholesterol and other fats build-up in the blood,
causing plaques to form and resulting in a susceptibility (predisposition) to
coronary artery disease. (McKusick 298)
While McKusick concludes that a very small percentage of the population carries the faulty gene, scientists have been able to confirm that age and gender also play a role in cholesterol levels found in the general population (299). Middle-aged men and women typically notice their cholesterol levels rise, and even though pre-menopausal women maintain lower numbers than men, once they reach menopause their numbers are equal to men.
Moreover, most researchers agree that diet has a strong impact on reducing the incidence of high cholesterol. Studies show that consuming high levels of saturated fats and some oils significantly increases the blood levels of LDL cholesterol.
Therefore, the current medical recommendations lean toward following a diet low in meat and dairy products, reducing overall fat consumption. Additionally, exercising regularly helps maintain proper weight and reduce cholesterol levels with the added benefit of improving overall cardiovascular health. A diet low in saturated fats and a consistent and age-appropriate exercise program go hand in hand with acceptable cholesterol levels. Patients with hypercholesterolemia who achieve their ideal weight as a result of diet and exercise typically see a reduction in cholesterol serum levels.
Also, bi-yearly check ups are recommended to assess the blood cholesterol levels of patients, as well as to allow the physician to better manage the blood test results (Henkel 24). A typical visit with the doctor includes a follow-up chart of weight and overall heart screening including normal pulse, respiratory capacity and any symptoms indicative of cardiac problems. Blood test results are analyzed for total cholesterol levels as well as individual LDL and HDL levels. Hemoglobin and other blood lipids, such as triglycerides are screened as well. Hemoglobin transports oxygen in the blood, a vital component for a healthy cardiovascular system.
Statin drugs are the prescription medicines of choice when diet and exercise are not enough to control hypercholesterolemia. They reduce blood cholesterol by blocking the synthesis HMG coenzyme A reductase, a liver enzyme necessary for producing cholesterol (Colpo 85). Furthermore, Colpo mentions that statins prevent the formation of plaque, and even reverse atherosclerosis, according to studies performed on laboratory rabbits (85). Additionally, and this is very important as it relates to the inflammatory nature of heart attacks, Colpo states that:
In research with mice, statins markedly reduce measures
of both inflammation and atherosclerosis, despite
little change in serum cholesterol levels. In humans,
statin therapy produces significant reductions in C-reactive
protein, a marker of inflammatory activity that has
repeatedly been associated with increased cardiovascular risk (86).
Pharmaceutical drugs such as Lipitor and Crestor are widely prescribed nowadays, with additional cardiovascular fringe benefits that go beyond lowering cholesterol levels, as mentioned in the previous paragraph (Colpo 86).
The synthesis and metabolism of cholesterol is a complex process that directly affects cardiovascular health. Regardless of family history, exercise, diet, and proper administration of prescription drugs successfully
help reduce overall cholesterol levels, including lowering the levels of LDL. However, as with any medical condition, more research is necessary to better understand the complexity of cardiovascular disease and exactly how elevated blood cholesterol and in particular low density and high density lipoproteins affect its onset.
Byrne, Kevin P. Understanding and Managing Cholesterol: A Guide for Wellness Professionals. Human Kinetics Books, 1991.
Colpo, Anthony. “LDL Cholesterol: Bad Cholesterol, or Bad Science?”
Journal of American Physicians and Surgeons Volume 10 Number 3 (Fall 2005): 85-86.
Henkel, John. “Keeping Cholesterol under Control.” FDA Consumer
Magazine. (January – February 1999): 22-24
McKusick, Dr. Victor A. John Hopkins Directory of Genetics Support
Groups, Services and Information (2006): 298-299