November 4, 2012
Cholesterol holds your cells together
Think back to your first chemistry or physics class. Never took chemistry or physics? Well, then imagine being in class where one of the first things your teacher wants you to know is that there’s no such thing as a solid substance.
Things that look solid — this book, that lamp, you, and me — are actually gazillions of individual atoms, molecules, and cells whirling around in space, held together only by an exchange of electrical charges. If you can’t remember much chemistry or physics, check out the “Recognizing the difference between an atom, a molecule, and a body cell” sidebar in this chapter. Mark your place, read the sidebar, and then come right back.
Okay, as I was saying, some things that look solid aren’t solid. They’re simply groups of cells held together by electrical charges that keep the cells in place so that a piece of this page or a piece of your finger doesn’t go spinning off into space. Individual cells stay intact because they have a cell membrane, an outer skin that serves as neat and tidy packaging for the cell.
One requirement for healthy cell membranes is — drumroll please — cholesterol. A whopping 90 percent of all the cholesterol in your body is in your cell membranes. The cholesterol protects the integrity of the cell membrane, helping to keep it flexible and strong.
If you were to diet so stringently or use so many cholesterol-lowering drugs that your cholesterol level fell to zero (an impossibility by the way), your cell membranes would be very dry and easily torn. The stuff inside the cells would leak out, and cells would die all over the place. That would sort of put an end to the whole darn shootin’ match. Every healthy body cell needs some cholesterol, and so does every healthy brain.
Recognizing the difference between an atom, a molecule, and a body cell
Atoms are the basic building blocks of elements — hydrogen, oxygen, carbon, and all their chemical cousins.
Each atom carries the name of the element it represents (such as hydrogen). In addition, each atom has a shorthand symbol — call it a nickname — such as H for hydrogen. Sometimes, an atom’s shorthand name seems totally divorced from its full name. For example, lead atoms are called, well, lead atoms, but the symbol for a lead atom is Pb, from plumbum, the Latin word for lead. There are also elements and atoms named for human beings. For example, seaborgium is named for Nobel Laureate Glenn T. Seaborg; its shorthand symbol is Sg.
Individual atoms form bonds with other atoms to create clusters of atoms called molecules. To write the name of a molecule — its formula — you write the symbols of the different atoms that the molecule contains and the number of each type of atom right after the symbol. For example, if I write H2O, the formula for the water molecule, you know immediately that a water molecule has two hydrogen atoms and one oxygen atom.
A body cell, the smallest independent unit of a living creature, is a collection of molecules. And you, wonderful reader, are a collection of cells.
Cholesterol helps your body develop
Cholesterol begins to influence your body even before you’re born. According to a 1996 report in the journal Science, cholesterol enhances an embryo’s healthy development by triggering the activity of the specific genes that instruct embryonic cells to become specialized body structures — arms, legs, spine, and so on. Sadly, as Science reported, approximately one in every 9,000 babies is born with a birth defect linked to the fetus’s failure to make the cholesterol it needs.
In 2003, researchers at the U.S. National Human Genome Research Institute linked a pregnant woman’s cholesterol deficiency to a defect in the fetal brain called HPE (the failure of the brain to divide normally into two halves). Ninetynine percent of embryos with HPE are spontaneously aborted; those born live experience severe mental retardation, are unable to walk or talk, and usually die within the first year of life.
To prevent these problems, pregnant women are often advised not to take cholesterol-lowering drugs.
Believe It or Not, You Need Cholesterol
Your healthy body needs cholesterol, but I haven’t told you the reasons why.
Let me list them now:
- Cholesterol directs the development of some cells in the growing fetus.
- Cholesterol is part of the membrane that surrounds and protects each cell in your body.
- Cholesterol comprises a major portion of your brain, which is composed of mostly fatty tissue.
- Cholesterol contributes to the construction of synapses, structures through which nerve cells transmit messages.
- Cholesterol is a building block for hormones, including the male sex hormone testosterone and the vital adrenal hormone cortisone.
- Cholesterol is an ingredient in digestive juices, such as bile.
- Cholesterol is used as a building block for vitamin D, which is made when sunlight hits the fatty tissue just under your skin.
- And, oh yes, cholesterol is part of body fat.
Is that an impressive list or what? I think it’s impressive as all get out, so I’m going to take some time to explain exactly how cholesterol performs each of these incredibly important jobs.
Pinning a blue ribbon on good lipoproteins
HDLs truly deserve the name “good cholesterol.” These particles don’t carry cholesterol into your arteries for the simple reason that they’re so compact and dense that they can’t squeeze through the spaces in the walls of your arteries. As a result, HDLs — and their cholesterol — travel away from your arteries and out of your body with the rest of your, um, solid waste.
What a neat set of facts to park in the back of your brain for the next time you’re at a party and someone asks you to explain the differences between VLDLs, IDLs, LDLs, and HDLs. “Well,” you can say, “it’s all a question of density, which, as you know, means. . . .” Don’t you just love being the smartest kid in class?
The good news about HDLs
You can think of HDLs as scavenger molecules that remove cholesterol from the arteries. Having a lot of HDLs reduces your risk of heart attack regardless of your total cholesterol levels.
In fact, X-ray studies have shown that people who raise their HDLs by exercising, stopping smoking, or taking medication not only reduce the cholesterol in the arteries but also remove the plaque — thus opening the arteries.
Having read that paragraph carefully, you may assume that all LDLs are bad guys, right? Wrong.
With LDLs, size may make all the difference
For years, everyone — that is, all the experts evaluating your cholesterol — conversely believed that a person with a lot of light and mushy LDLs (which can squeeze through your artery walls) inevitably had a higher risk of heart attack. The fact that some people with high levels of LDLs sailed happily into old age without experiencing heart problems was dismissed as plain good luck.
Maybe not, says a group of researchers at Albert Einstein College of Medicine in New York City. In 2003, looking for clues to longevity, the team, which included members from the University of Maryland School of Medicine, Tufts University, Boston University School of Medicine, and Roche Molecular Systems, ran various tests, including cholesterol tests, on 213 senior citizens, plus 216 of their children and grandchildren. For comparison, they ran the same tests on a control group of non-blood relatives, such as the children’s husbands and wives.
The tests showed something really surprising: The long-lived oldsters were three times more likely than other people to have a mutation in a gene that regulates cholesteryl ester transfer protein (CETP), an enzyme that affects the size of lipoproteins. As a result, compared with other people, including those non-related husbands and wives, even the oldsters who had high levels of LDLs had relatively larger low-density lipoproteins. (Their HDLs were also relatively bigger.)
According to the Einstein team, led by Dr. Nir Barzilai, the level of LDLs doesn’t predict heart disease; it’s the size of the LDLs in the mix. In other words, having many small LDLs may raise the risk of heart attack even if your overall cholesterol level is low. Definitely more to come on this one.
Moving through the fat factory
As anyone who has ever read a nutrient chart knows, liver (as a food) is very high in fat and cholesterol. In fact, your liver is a veritable fat and cholesterol factory that collects fat fragments from your blood and uses them to make cholesterol and new fats that your body can use to build tissue and perform other physiological functions.
The next few sections explain exactly how lipoproteins are made.
Putting the fats in lipoproteins (and taking them out again)
When the chylomicron hits the liver, it picks up fat particles and mutates into the largest kind of lipoprotein, a fluffy particle called a very low density lipoprotein (VLDL).
Then your liver sends the VLDL out into the wide world — your body. As the VLDL travels far and wide, it drops globs of fat, picks up globs of cholesterol, and changes into a slightly smaller, heavier particle called an intermediate low-density lipoprotein (IDL), and then a slightly smaller, heavier low density lipoprotein (LDL).
The last step in the transformation of the baby lipoprotein (the chylomicron) occurs when an LDL has dropped so much fat and cholesterol into body tissue that it’s mostly protein. Now, you’re looking at a high density lipoprotein (HDL).
Naming the proteins in lipoproteins
The primary proteins in VLDLs, IDLs, and LDLs belong to a class of apolipoproteins called apoB. The primary proteins in HDLs belong to a class of apolipoproteins called apoA. Other less prominent apolipoproteins found in lipoproteins are apoC and apoE.
You may have heard about a blood test for apoA; this test is interesting because a high level of apoA indicates a high level of protective HDLs (the “good” particles that haul cholesterol out of your body).