For close to five decades we have been led to believe that cholesterol is bad for our body, that it is a major causative factor for cardiovascular disease that is, coronary artery disease, strokes (“brain attack”) and related ailments. This translated into a rash of advisories and guidelines admonishing us to consume a diet low in fats and cholesterol, keep our weight in check and in extremis, even resort to medication to lower our cholesterol levels in case they were found to be elevated. However, recent evidence has tilted the balance to the contrary. In scientific terms, cholesterol is not quite the villain it has been made out to be. In fact, this compound is actually an essential part of our body cells. Each and every cell in our body is bounded by a membrane, which is a complex structure that is composed of lipids, a form of cholesterol. This substance is also a vital part of the chemical composition of Vitamin D and many other important hormones of the body. However, how exactly has cholesterol come to assume the status of the villain of the piece? A simple explanation follows:
Blood levels of cholesterol are considered in terms of lipoproteins, which are substances that transport cholesterol through the blood. The structure of lipoproteins is comprised of a core of lipid or fat, surrounded by a matrix of proteins. There is a whole series of lipoproteins but the two fractions most relevant to heart disease are High Density Lipoproteins (HDL) and Low Density Lipoproteins (LDL). LDL, which comprises 60-70% of total blood lipoproteins, has been called the “bad” cholesterol, as it has been linked to atherosclerosis (buildup of cholesterol plaques in arteries). The actual number of LDL particles has been linked to a correspondingly higher risk of heart disease.
HDL particles, on the other hand are responsible for transporting excess cholesterol to the liver for metabolism or breakdown. By this mechanism, they are considered to exert a protective effect against cholesterol plaque buildup in the arteries, which has led them to be dubbed “good” cholesterol.
This brings us to the topic of contention: what is the relation of our diet to blood levels of cholesterol? Logic would dictate that there exists a direct relation between the two that is, the more the dietary levels, the higher the blood levels of cholesterol. Simplistic as that may sound, it is not the way the body works. The majority of our body cholesterol is produced by the liver, and this is sensitive to dietary intake in the form of a feedback loop mechanism. That is, the more cholesterol we hog in our diet, the less our liver churns out, and vice versa. Simply put, as long as our liver is fighting fit, our blood cholesterol levels are well regulated, with the liver producing as much as is needed for the essential roles played by cholesterol as outlined above. As far back as 2009, an interestingly named study, the Harvard Egg Study found that there was no conclusive evidence to back the claim that increased egg (obviously!) consumption was associated with an increased risk of cardiovascular disease. This was applicable to normal subjects in which the feedback loop as mentioned above (where the liver cuts back production consequent on an increased dietary cholesterol intake) was normal.
The causation of cardiovascular and especially, heart disease is now known to be multifactorial. It is common knowledge that diabetes, smoking, hypertension and a strong family history of heart disease are significant risk factors in the causation of coronary artery disease. It has also been found that diabetes is associated with a defect in the feedback loop that regulates inherent cholesterol production by the body in response to dietary cholesterol. Besides this, diabetes is also associated with damage to blood vessels at the microscopic level. Cardiovascular disease has also been found to be caused by an inflammatory process, the exact mechanism of which is still under investigation. Hence, the mere existence of a raised blood cholesterol level may not suffice to cause cardiovascular disease. Rather, it may do so ONLY in the presence of the other risk factors as mentioned above.
The take-home message thus may be crystallized as thus:
1. Dietary cholesterol is NOT the villain it has been made out to be.
2. Dietary cholesterol has no direct correlation to your blood levels subject to certain caveats like, a normal liver function and the absence of other conditions that may affect cholesterol metabolism like diabetes, or genetically determined high cholesterol levels. However, high cholesterol levels are a definite risk factor for heart disease.
3. This does NOT mean that we may proceed to stockpile on greasy, gooey stuff like jalebis and samosas! This is because, while they may not necessarily lead to high blood cholesterol levels, they will still lead to a widening of our midriffs and weight gain. These two factors have been found to have a direct correlation with the causation of cardiovascular disease. Indeed, a simple/difficult (depending on one’s perceptions!!) way to lower your blood cholesterol is through exercise and weight loss.
4. We must focus on keeping our blood cholesterol levels at a healthy clip, but should shed the belief that diet ALONE is responsible for elevated levels.
Teaser: who then is the actual dietary villain of the piece, if not cholesterol? That, my friends will be revealed in our next article! Until then, keep fit, keep moving!
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Dr. A. Kundu, Consultant Cardiac Surgeon, National Heart Institute New Delhi |
