Part I
Americans are conscious of cholesterol as never before, but not necessarily clearer about what it all means. Some of us know our blood cholesterol levels almost as ‘well as our phone numbers. Books ‘about cholesterol appear on best seller lists, and more and more foods are suddenly sporting the label “cholesterol free”. But 79% of us don’t even know what our cholesterol levels should be, let alone ‘what they are, according to one recent poll. If you’re like most people, you’re tripped up by some fundamental questions.
CONFUSION #1: Does the cholesterol in your blood come from the cholesterol you eat?
Actually most of the ‘cholesterol in your blood is manufactured in your body, primarily by the liver. The body produces varying amounts, usually about 1,000 milligrams a day, from the fats, protein and carbohydrates you eat. In addition, the average American consumes 400 to 500 milligrams ‘of cholesterol in food every day. So, in a sense, we talk about two different “types” of cholesterol though chemically they’re the same the kind’ we eat in food (called dietary, or preformed, cholesterol) and that made by the body both 6f which end up in the blood.
Cholesterol is a waxy, fatlike substance classified as a lipid. It is found in all animals and thus in all animal products we eat meat, eggs, fish, poultry, and dairy products (no plant derived food contains cholesterol). Though we usually think of it as being in the bloodstream, its actually in all tissues in humans as well ‘as in other animals. Cholesterol is essential to life: it is used to form all cell membranes certain hormones and other vital substances. The body makes all the cholesterol it needs, so it isn’t an “essential nutrient”. In other words you don’t need to consume any to stay healthy.
Too much cholesterol can build up in the bloodstream, accumulating in the walls of the blood vessels, 4 condition known as atherosclerosis. Nodules, called plaques are formed decreasing the flow of blood and favoring the formation of blood clots. This may ultimately cut off the flow of blood, in the conorary arteries this leads to a heart attack and in the cerebral arteries, a stroke.
CONFUSION # 2: Which foods contain “good” cholesterol?
You can’t eat “good” cholesterol. No type of cholesterol you eat is good for you. What’s called good cholesterol is actually high-density lipoprotein, HDL, a complex particle that’s assembled in the liver and circulates in the bloodstream. HDL has been much in the news lately (it made the cover of Time in December), leading some bewildered consumers to search for it in their supermarket aisles.
Just how cholesterol is distributed through the body is not entirely clear, but researchers how hypothesize that the mechanism works like this: the liver puts together packages called lipoproteins, made of proteins, cholesterol, and triglycerides (fats either made by the body or derived directly from foods). The larger of these are called very low density lipoprotein, or VLDL, As it circulates through the system, VLDL drops off the triglycerides to the muscle and fat cells to be used for energy or stored for later use. When VLDL drops off its triglycerides, it breaks up into smaller low-density lipoprotein, or LDL. The LDL then carries the cholesterol through the system dropping it off where it is needed for cell building. and leaving unused residues of cholesterol in the arterial walls.
As it circulates in the bloodstream, HDL seems to be able to pick up cholesterol and bring it back to the liver for reproduction or exertion. In simple terms, then, LDL, brings cholesterol into the system So it’s often called bad cholesterol. And because HDL clears cholesterol out of the system, it has been dubbed good cholesterol. If you have trouble remembering which is which, think “lousy” for LDL and “helpful” for HDL.
CONFUSION #3: Who should worry about HDL?
This is currently being hotly debated, in light of the findings of at least four recent studies that boosted the importance of HDL. Researchers found that people with “safe” total cholesterol levels below 200 milligrams per deciliter (mg/dl) may still be at risk for coronary artery disease (CAD) if their HDL levels are low; and, inversely, that some people with elevated total cholesterol levels (usually women) may not be at high risk if their HDL levels are high. On the basis of these studies, some scientists now recommend that HDL be measured in all people with risk factors for CAD even if their total cholesterol levels are low.
Average HDL levels in adult Americans are about 45 to 65 mg/dl with women ranging higher than men. The new studies suggest that levels above 70 may protect against CAD, while those below 35 signal coronary risk. Female sex hormones tend to raise HDL, this may help explain why women are usually protected against atherosclerosis during their childbearing years, when estrogen production is high.
Ultimately, despite the headlines, the new research on HDL hasn’t significantly changed the way we understand or treat high cholesterol. It’s a matter of emphasis. Until now, physician have focused on elevated total cholesterol and LDL because the evidence linking them to heart disease is substantial. But when they look at LDL, doctors normally also look at HDL in order to get the whole picture.
At this point research on HDL is still in its early stages. No clinical study has demonstrated that people with low HDL levels can actually decrease the risk of coronary disease solely by raising these levels. Complicating matters is the fact that there are different types, or subclasses, of HDL and LDL, which interact in complex ways and appear to have different effects ‘on coronary risk. Only future research will tell whether a low HDL level is the key risk factor for CAD or just one element in the equation.
To Be Continued
Article extracted from this publication >> April 21, 1989