Cholesterol
What is cholesterol? What do you think it is or means and how do we get it?
Well?
“Cholesterol” is a component of the several kinds of fat in our blood. Frequently however, it is a generic term used to refer to all the fats in our blood. When we doctors check your cholesterol level, we are in reality checking several of the more important fat components of the blood, that make up a lipid profile, which should be the appropriate term used. Our bodies produce, cholesterol and fats. Around 20–25% of our total daily cholesterol production occurs in the liver. Other sites of production include the intestines, adrenal glands and reproductive organs. This is why there are some people who may have an ideal weight, exercise regularly and eat healthy, yet may have elevated lipids. Genetically, excess cholesterol is either being produced or inappropraitely/incompletely eliminated. Cholesterol and lipids is needed for our bodies to function healthy, and lipids among other important roles, serve as the building blocks for hormones. In addition to the main “fats” produced and absorbed by our bodies, total cholesterol (TC) and trigycerides (TGL), there are several groups of lipoproteins such as chylomicrons, very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density lipoproteins (LDL) also referred to as “bad” cholesterol and high density lipoproteins (HDL) referred to as “good cholesterol” whose function is to enable lipids like cholesterol and triglycerides to be transported within the water based blood stream.
Total cholesterol (TC) is the main “fat” if you will, and again is transported to and from the cells by the carrier fat molecules, lipoproteins, as just explained. During a lipid profile in addition to TC and TGL, we also routinely measure HDL and LDL. The other lipoprotein particles can also be measured however these are in small concentration and their presence is not significant enough to be routinely checked.
Continuous study and research over the years have lead to current recommendations of ideal and desired levels of these lipids, which by the way have continued to be decreased with subsequent updates. Typically in patients with coronary artery disease (CAD) or risk factors for CAD, those who have had a heart attack, diabetes, congestive heart failure, hypertension etc, the desired or goal levels are lower than that for the general population. Currently the consensus panel has indicated that we should strive to achieve a TC level of less than 200mg/dl. From 200-239mg/dl, borderline high and values above 240mg/dl is considered high. In persons with coronary artery disease (CAD), risk factors including diabetics, the lower the level, the better. My heart disease patients are encouraged to reach and maintain TC levels be below 190mg/dl. As I previously mentioned, our bodies produce cholesterol and can normally remove excess fats from the blood. In situations when we find elevated lipid levels in circulation, depending on how the fat is transported within lipoproteins, and the length of time the elevation exists can lead to the progression of “hardening of the arteries” or atherosclerosis. Cholesterol is also recycled. It is excreted by the liver via bile into the digestive tract. Typically about half of the excreted cholesterol is reabsorbed by the small intestine and eventually goes back into the blood stream, while the other, typically more atherogenic components of the fats, flow back into the intestinal lumen for elimination.
As mentioned before, in the liver, cholesterol is converted to bile, which is then stored in the gallbladder. Bile is important because contains bile salts, which function to make fats soluble in the digestive tract and aid in the intestinal absorption of fat molecules as well as the fat soluble vitamins, Vitamin A, Vitamin D, Vitamin E and Vitamin K. Cholesterol is also an important precursor molecule for the synthesis of the steroid hormones, including the adrenal gland hormones including cortisol as well as the sex hormones progesterone, estrogens, and testosterone.
Another important lipid or lipoprotein that is measured during a “cholesterol” check is Triglycerides (TGL). This is a form of lipid used in transportation of the fat molecule along the blood stream, therefore its level gives us an indication as to the numbers or concentration of fat molecules floating around the circulation. Normal levels are below 150. Triglyceride is also synthesized in the body. Elevated triglycerides can be due diet, seen in persons who are overweight, are obese, physical inactive, smoke cigarettes, with excess alcohol consumption and diets high in carbohydrates. People with high triglycerides often have a high total cholesterol level, including a high LDL (bad) level and a low HDL (good) level. Many people with heart disease and/or diabetes also have high triglyceride levels. Triglycerides in plasma are derived from fats eaten in foods or made in the body from other energy sources like carbohydrates. Calories ingested in a meal and not used immediately by tissues are converted to triglycerides and transported to fat cells to be stored. This is one reason we should eat more frequent, small amount meals as opposed to one or two large meals a day. Hormones regulate the release of triglycerides from fat tissue so they meet the body's needs for energy between meals.
LDL, low density lipoproteins, or the so called “bad cholesterol”. The purpose of low density lipoprotein (LDL) is to transport cholesterol and triglycerides from the liver to peripheral tissues. Bad, because when too much LDL cholesterol circulates in the blood, it can slowly build up in the inner walls of the arteries, including the arteries that feed the heart and brain. With time and with the addition of other circulating substances and chemicals, direct deposition of these fat particles or atheromas occur in the blood vessel walls contributing to plaque build up and atherosclerosis. Levels should be kept to less than 100mg/dl and people with heart disease or risk factors, lower at below 70mg/dl. Plaque or atheromas can form thick, hard deposits inside the lumen of arteries that can narrow the arteries and make them less flexible. This is known as atherosclerosis. As explained in the section on stress tests, if a clot was then to form and block a narrowed artery, heart attack or stroke can result. Remember that LDLs transport cholesterol to the arteries, can be retained there, and can start the formation of plaques, increasing the process of atherosclerosis, and heart attack, stroke, as well as peripheral arterialr disease (PAD). The cholesterol transported inside LDL lipoproteins is often referred to as bad cholesterol, yet we need to remember and understand that the cholesterol contained in LDL is the same kind of cholesterol as transported by other lipoproteins. In and of itself is not worse or any “badder” if you allow me to state it that way, than the other forms of fats and cholesterol. The reason why LDL gets the reputation as bad, has to do with the way the cholesterol is being transported, to where the cholesterol is being transported, and more importantly the amounts over time being transported all of which contribute to causes adverse effects.
Lp(a) Cholesterol
Lp(a) is a genetic variation of LDL (bad) cholesterol. A high level of Lp(a) is a significant risk factor for the premature development of fatty deposits in arteries. Lp(a) isn’t fully understood, but it may interact with substances found in artery walls and contribute to the buildup of fatty deposits.
HDL, HDL-C, high density lipoproteins or ‘good cholesterol”. In direct opposite of the rest of the lipoprotein values, with HDL, the higher the number, the better. HDL provides protection against heart disease. Levels should be kept above 40 in women and 50 in men. Medical experts think that HDL tends to carry cholesterol away from the arteries and back to the liver, where it's removed and excreted from the body. Some believe that HDL also contributes in removing excess cholesterol from the arterial plaque, retarding its growth and slowing its buildup. This is why HDL-bound cholesterol is referred to as good cholesterol. A high level of HDL seems to offer protection against cardiovascular diseases, while low HDL cholesterol levels increase the risk for heart disease.
So now that you have the basics lets review it to try to make it clearer. Cholesterol and triglycerides are the major lipids produced by the body and obtained also from our diets. Hence why we recommend a low fat diet as the first step for people who have high cholesterol levels. These lipids are then transported throughout the blood stream through arteries and blood vessles via carrier molecules called lipoproteins. The most common of these lipoproteins are HDL, and LDL. These four make up the lipids we check when you check your cholesterol levels with a lipid profile. This blood test is done after a 12 hour fast.
Now I would like to share with you another interesting and important finding in regards to lipids, specifically in regards to LDL. For a long time doctors had been seeing some patients, who had normal levels of cholesterol yet who developed CAD and atheromas, conditions typically associated with high cholesterol levels. This was a curious yet misunderstood finding which was finally explained by researchers. We understood fairly well the complex processes involved in the synthesis, distribution and elimination of cholesterol and triglycerides as well as the mechanism of action of the lipoproteins. What was recently identified was that the SIZE of the fat particle, specifically the size of the LDL particle had its own independent significance. Small, dense LDL particles have been shown to be more atherogenic than larger LDL particles.
Researchers referred to the small dense LDL particles as "pattern B", and a larger and less dense LDL particles as “pattern A". The reason that the smaller, denser particle of pattern A, are more atherogenic or dangerous in the development of heart disease than the larger molecule pattern, equating to a higher risk factor for coronary heart disease, is because the smaller particles are more easily able to penetrate the walls of the endothelium (the cells that line the inside of the blood vessle).
Recap: atheromas and plaque buildup is related not only to the amount of lipid particle but also to the size and numbers of the particular LDL particle both of which are importance in the development of atherosclerosis. Atherosclerosis, is inflammation and as such, we can detect degrees of inflammation with blood tests. This little tease will be expalined later on. (Keep reading)!
So now I hope you have a better understanding and knowledge about cholesterol, an extremely important subject as it is a main contributor to heart disease. Important also for the simple fact that it is modifiable and controllable.