Friday, March 27, 2009

Will Eating Meat Make Us Die Younger?

by Chris Masterjohn

A widely reported and blogged about study conducted by the National Institutes of Health, published Monday in the American Medical Association's Archives of Internal Medicine, found that among over a half million followed from 1995 to 2005, those who reported eating the most meat were more likely to die than those who reported eating the least meat.

The accompanying editorial was written by Barry Popkin, an economist who used to work for the Rockefeller Foundation and is currently a fellow of the Carolina Population Center, an organization started by the Ford and Rockefeller Foundations in the 1960s as part of their effort to institute worldwide population management programs. Popkin recommended reducing saturated fat to less than seven or ten percent of calories, requiring "higher-income countries to significantly cut their animal source food intake, shift to leaner meats, and shift to reduced-fat dairy products." Strangely, he left out any discussion of the relationship between low-fat dairy products and infertility; this relationship would certainly make switching to low-fat dairy products a good form of population control. He concluded that practicing clinicians should avoid preaching vegetarianism but rather advise a general reduction in the intake of animal foods, to prevent chronic disease and global crises of food, water, and climate.

News reports claimed that the study showed eating the equivalent of a quarter-pound hamburger per day "gave" men and women 20-50 percent increases in the risk of chronic diseases such as cancer and heart disease. In reality, the study showed no such thing. It was not designed to determine cause and effect, and its ability to determine true meat intake was almost non-existant. News reports and editorials alike failed to discuss its embarassing finding that meat intake was associated with the risk of dying from accidental injury, probably because the apparent lack of a plausible mechanism by which eating meat could cause someone to get into a car accident emphasizes the most basic principle of science that they want us all to forget: that correlation does not prove causation.

There are thus two important points we need to understand about this study to realize just how little it does to increase our knowledge:

  • The study found a correlation between increased mortality and a population's propensity to report eating meat, not a correlation between mortality and true meat intake. As we will see below, these may be two completely different things.
  • Correlation does not show causation. There is absolutely no scientific basis to conclude from this study that eating meat increases mortality.
These types of studies are useful to generate new hypotheses, but this study failed to do even that. As we will see below, it therefore provides us with no useful information of any kind.

Reported Meat Intake — Is It Related to True Meat Intake?

Beginning in 1995, the authors of this study gave a food frequency questionnaire (FFQ) to over a half million people. You can view the questionnaire here. It contained 124 questions, each question about a particular type of food or group of food. It asked the participant how often she or he consumed the food over the course of the last year, giving them ten options. Then it asked how large of a serving size they consumed, giving them usually three or four options. Sometimes they were given additional instructions, like including sandwiches in some cases or excluding sandwiches in other cases.

Obviously any individual trying to quantify his or her average intake of 124 foods over an entire year is going to have to engage in a lot of guess work. Even 24-hour recalls of what a person ate the day before are subject to a great deal of error. For this reason, researchers will commonly "validate" an FFQ or a 24-hour recall to test whether these accurately measure the intake of the foods of interest. In order to do this, they have the participants make a weighted dietary record where they meticulously weigh everything they eat with a dietetic scale and record it as they prepare each meal. Then the researchers compare the FFQ or 24-hour recall to the weighted dietary record, assuming that the weighted dietary record is the best indicator of true dietary intake.

The researchers who published the red meat study did this differently. They "validated" their FFQ with two 24-hour recalls!

This is rather strange. Consider how the researchers who conducted the Nurses' Health Study described the need for validation:
The role of diet in disease processes is of great scientific interest. One limitation in assessing associations between diet and disease is the often-large measurement error in reported dietary intake, which arises from two major sources. First, there is random within-person variation in reported dietary intake based on commonly used instruments such as a food frequency questionnaire (FFQ) or a 24-hour recall. Second, even if a surrogate instrument (e.g., FFQ) were perfectly reproducible, it might not be a valid measure of true dietary intake as might be captured in a weighed diet record, in which subjects record what they eat on a real-time basis.

To address the validity issue, it is becoming common to conduct a validation study. A small subset of persons, ideally from the same population as the main study, are administered both the surrogate instrument (e.g., FFQ) and a "gold standard" instrument (e.g., diet record) and the relation between them is ascertained.
If the FFQ and the 24-hour recall are both "surrogate instruments" in need of validation with a directly measured dietary record, how can a 24-hour recall instead of a dietary record be used to validate an FFQ? Obviously, it can't.

Moreover, the authors' "validation study" found that the "true intake" of protein, carbohydrate, fat, cholesterol, fiber, vitamins, minerals, fruits, and vegetables estimated by the 24-hour recall could explain between 5 percent and 45 percent of the variation in the participants' answers on the FFQ, but they never "validated" the FFQ's ability to predict the "true intake" of meat!

It is therefore bizarre to say the FFQ was "validated" at all.

Fortunately, the researchers who conducted the Nurses' Health Study (Harvard) conducted it far more rigorously than the researchers who conducted this study (the Federal government), so their research can give us an idea of just how foolish it is to believe that answers to questions about meat on an FFQ represent true intake of meat.

Researchers conducting the Nurses' Health Study have administered and continue to administer FFQs repeatedly to the study's participants to track food intake over time. They validated their FFQ with four seven-day weighted dietary records, each given three months apart. Their validation therefore takes into account day-to-day variation within the week as well as seasonal variation during the year.

They found that the FFQ predicted true intake of some foods very well and true intake of other foods very poorly. True intake of coffee could explain 55 percent of the variation in answers on the FFQ, while true intake of beer could explain almost 70 percent. True intake of skim milk and butter both explained about 45 percent, while eggs followed closely behind at 41 percent.

But the ability of the FFQ to predict true intake of meats was horrible. It was only 19 percent for bacon, 14 percent for skinless chicken, 12 percent for fish and meat, 11 percent for processed meats, 5 percent for chicken with skin, 4 percent for hot dogs, and 1.4 percent for hamburgers.

If your jaw just dropped, let me assure you that you read that right and it is not a typo. The true intake of hamburgers explained only 1.4 percent of the variation in people's claims on the FFQ about how often they ate hamburgers!

What explained the other 98.6 percent of their answers on the FFQ? One possibility for which there is substantial evidence is that some foods are, in our culture, socially and emotionally charged, and participants are more likely to lie about their intake of those foods, or more likely to deceive themselves about how much of those foods they are really consuming. Consider what the researchers who validated the Nurses' Health Study FFQ had to say:

Focusing on the second questionnaire, we found that butter, whole milk, eggs, processed meat, and cold breakfast cereal were underestimated by 10 to 30% on the questionnaire. In contrast, a number of fruits and vegetables, yoghurt and fish were overestimated by at least 50%. These findings for specific foods suggest that participants over-reported consumption of foods often considered desirable or healthy, such as fruit and vegetables, and underestimated foods considered less desirable. . . . This general tendency to over-report socially desirable foods, whether conscious or unconscious, will probably be difficult to eliminate by an alteration of questionnaire design.
The implications are even worse than suggested in this quote. The authors looked at the results from two FFQs, one administered three to six months before the first dietary record was taken, and a second one administered a year later, on the immediate tail of the third or fourth dietary record. In other words, the results from the second FFQ should be more accurate because the participants had just spent a week meticulously measuring and recording everything they ate. So the tendency to exaggerate intakes of socially desirable foods and under-report intakes of socially undesirable foods was probably even greater on the first FFQ, and thus even greater on an FFQ in the current NIH-red meat study, in which no dietary record was ever administered.

If true intake of hamburgers represents 1.4 percent of the variation in intakes as estimated by the FFQ, and other factors such as a person's willingness to deceive themselves about how much hamburger they are eating or, worse, lie about how much hamburger they are eating explains at least a substantial portion of the other 98.6 percent, would you believe any study finding correlations between hamburger consumption and some health endpoint was actually testing the effect of eating hamburgers? I wouldn't.

We must therefore be careful to say that the NIH study found an association between increased mortality and someone's willingness to report consuming red meat to researchers from the Federal government. We must carefully avoid saying that the study found an association between mortality and actually eating red meat.

Remember the Scientific Method — Correlation Does Not Prove Causation

Every student learns this most basic fact of science in any introductory science course: correlation does not prove causation. If A increases as B increases, this may be because A causes B, but it may also be because B causes A or because a third factor C causes them both.

The NIH study found that people who reported eating more red meat were more likely to be married, to be white, to smoke, to eat more food in general, to weigh more, to be less educated, to take vitamin supplements less often, to eat fewer fruits and vegetables, and to exercise much less often. In fact the proportion of people that engaged in vigorous physical activity among those who reported high intakes of red meat was only 16 percent, hardly more than half of the proportion of people that engaged in vigorous physical activity among those who reported low intakes of red meat, which was 30 percent.

Researchers call these confounding variables and use statistical methods to try to control for them. But there are always other confounders that the researchers do not know about. For example, this paper did not report statin use among participants. Since these drugs are extremely common among elderly people and are believed to affect lifespan, could they not present us with another confounding variable? Are people who report eating more red meat more or less likely to be placed on statins?

The potential number of confounders is limited only by our imaginations. This is why we never, ever use epidemiological studies that uncover correlations to demonstrate causation.

To illustrate the pitfalls of confusing correlation with causation, let us consider this: the study found a 26 percent increase in the risk of "mortality from injuries and sudden deaths" among those who reported eating the most red meat. It is entirely possible that eating red meat could increase the risk of injury, but is it probable? Not very. So the news reports and editorials have largely ignored this finding in favor of the increase in heart disease and cancer risk it found, because it seems intuitively more reasonable to most people that eating meat could cause these diseases.

The strongest correlation, however, was between eating red meat and the risk of "all other deaths," a category that included mortality from tuberculosis, HIV, other infectious and parasitic diseases, septicemia, diabetes, Alzheimer disease, stomach and duodenal ulcers, pneumonia and influencza, chronic obstructive pulmonary disease and related conditions, chronic liver disease and cirrhosis, nephritis, nephrotic syndrome and nephrosis, congenital anomalies, certain conditions originating from the perinatal period, ill-defined conditions, and unknown causes of death.

In order to begin laying down a solid hypothesis that reporting eating red meat (which is falsely assumed to represent actually eating red meat) actually causes death from all of these diseases, the authors need to make an argument that causation is biologically plausible. And that is just to present the hypothesis. In order to begin confirming the hypothesis, studies in cells, animals, and eventually humans are needed to show that modifying red meat intake controls the risk of these diseases.

The authors have another large obstacle before them: reporting a high intake of white meat was associated with a lower risk from almost all of these deaths! But the chemical constitutents of red meat that the authors of this paper blame for causing disease — carcinogens formed during high-temperature cooking, iron, and saturated fat — are also found in white meat.

Epidemiological studies such as this one are observational in nature. Observation is the first step of the scientific method. One then develops a hypothesis to explain those observations, and then tests the hypothesis through experimentation. Epidemiological studies, therefore, are useful for generating hypotheses, but not for testing them. They could also be used to quantify the importance of a risk factor once it is already established to cause the health-related endpoint with which it is associated through experimentation.

Red meat has not already been shown to cause early death, so this study cannot be used to quantify its importance as such a cause. The hypothesis that red meat causes all sorts of disease already exists, so this study cannot be used to generate a new hypothesis.

If this study had analyzed red meats of different quality separately, it may have shed light on a new hypothesis. It could have analyzed grass-fed versus grain-fed meat. It could have analyzed meat from animals raised on pasture grown in soils of different quality. It could have analyzed how well the meat was cooked. But it did none of these things.

The study therefore provides us with no more useful information than we already had. In fact, by using an unvalidated food frequency questionnaire that most likely had almost no ability to actually estimate true intake of red meat, the study just adds more confusion to the multitude of conflicting claims about the relationship between diet and health. This is where our tax dollars are going to, at least the portion of them that is not going towards bailing out the big banks. Meanwhile, I will continue to eat red meat.

Read more about the author, Chris Masterjohn, PhD, here.

Sunday, March 22, 2009

Do Blockages In Coronary Arteries Really Cause Heart Attacks?

by Chris Masterjohn

Last weekend I was invited to speak at the Freedom Law School's 2009 Health and Freedom Conference, which was an interesting mix of nutrition and politics, the latter portion largely devoted to opposition to the income tax, opposition to the Federal Reserve, and alternative theories about what happened on September 11, 2001. I don't agree with all of the political views expressed, but I found the political talks enjoyable and thought-provoking. They asked me to speak about the health benefits of eating animal fat, which of course I was happy to do.

Knowing very little about the organization, I did not expect an award. But the head of the organization, Peymon Mottahedeh, is an extremely generous and warm-hearted person who obviously loves to give awards since he gave out about twelve of them. He gave one to me. The plaque reads, "Freedom Law School, In Recognition of Your Tenacious Efforts to Find Health Solutions And Expose the Truth About Cholesterol, Recognizes You, Chris Masterjohn, As A Health Freedom Fighter."

While Richard Gage, the founder of Architects and Engineers for 9/11 Truth, gave the talk that provided the most compelling evidence-based alternative to a mainstream dogma, it wasn't the most radical talk when one considers that over a third of Americans believe there was some government complicity or direct involvement in the attacks. (Of course, A&EFor9/11Truth does not promote this idea directly, but rather analyzes the physical evidence demonstrating explosives were used in the WTC building collapses and demands an investigation of this matter, without placing blame on any particular group).

The most radical talk was Dr. Tom Cowan's. He argued that blockages in coronary arteries do not cause heart attacks. Heart attacks, according to his view, cause blockages in coronary arteries. The real cause of heart attacks is a buildup of lactic acid in the cells of the heart muscle. (He has also written an article on this here.)

Well, everyone agrees that a buildup of lactic acid in the heart muscle is what causes heart attacks. The difference is what is believed to happen before this. The mainstream view is that, in most cases, direct rupture of an atherosclerotic plaque in the coronary artery leads to a blood clot, which then blocks the artery and deprives the heart muscle of oxygen. In a large minority of cases, the endothelial lining above the plaque erodes, leading to a clot. In a smaller minority of cases, the plaque itself becomes so severe that it occludes the artery. Cowan's view, shared by other scientists mostly based out of Brazil, is that capillary dysfunction, not artery blockage, deprives the heart muscle of oxygen.

At some point in the future, I will thoroughly research this issue and present my conclusions.

For the time being, I could like to present one important argument that should leave a quiet unease in anyone who believes that atherosclerotic plaque is not at least one major cause of heart attacks: the genetic evidence that the activity of the LDL receptor can almost completely control the risk for heart attacks.

Goldstein and Brown won a Nobel Prize in 1985 for their discovery of the LDL receptor in the 1970s. They have written a new review of the LDL receptor that provides a historical overview.

Goldstein and Brown are remarkable scientists, but they have made some unscientific public statements. On the homepage of this site, I quote them describing researchers and physicians as militant warriors against cholesterol rather than inquisitive and helpful people searching for truth. Nevertheless, as some say, God gave us two ears and only one mouth for a reason, so rather than looking for an excuse not to listen to them, we should gratefully learn from their expertise. We should also nevertheless critically evaluate the evidence they provide, because God gave us a mind too.

The LDL receptor brings LDL into cells. Familial hypercholesterolemia is a genetic defect in the LDL receptor. One in 500 people are heterozygous for this condition, meaning they have one copy of the defective gene, resulting in half the quantity of active LDL receptors and twice the concentration of LDL in the plasma. One in a million people are homozygotes, people with two copies of the defective gene. They have 6-fold to 10-fold elevations in plasma LDL levels.

Heterozygotes develop atherosclerosis early and begin having heart attacks as early as age 30. Although they only constitute 0.2% of the population, they constitute 5% of people who have heart attacks before the age of 60.

Homozygotes develop atherosclerosis much, much earlier, and can have heart attacks in childhood. Homozygotes have cholesterol deposition in many other places besides arteries, like the extreme versions of the cholesterol-fed rabbit model. As in arterial plaques, this cholesterol comes from the accumulation of oxidized LDL into macrophages (immune cells), which is a phenomenon mediated not by the cholesterol but by the oxidation of the polyunsaturated fatty acids (PUFAs) in the LDL membrane, which in turn damages the protein in the membrane, leading the immune system to mop it up before it wreaks havoc on every cell it encounters.

Homozygotes, according to case reports I have found, have died of heart attacks as early as age 3. I have read reviews claiming death even in two-year-olds.

As I pointed out in Issue #14 of my free newsletter, a genetic mutation in the enzyme that degrades the LDL receptor has the opposite effect, increasing the expression of the LDL receptor and reducing the risk of heart disease by 88 percent, nearly abolishing it.

This suggests that LDL receptor activity has almost complete control over the risk of heart disease: when it is low, one gets heart attacks earlier; when it is absent, heart attacks can occur in young children; when it is high, one is almost guaranteed freedom from a heart attack.

Now, what exactly does the LDL receptor do that can affect the risk of heart disease?

As Goldstein and Brown recount in their review, they found that cells tightly regulate their cholesterol synthesis in response to the cholesterol provided them from LDL. In a normal cell, LDL will suppress cholesterol synthesis by delivering cholesterol to it. In a cell from someone homozygous for famililal hypercholesterolemia, however, the cell cannot take in LDL, so its cholesterol synthesis remains very high at all times. Thus these cells are not suffering from cholesterol deficiency. They are making plenty of their own cholesterol, as much as a normal cell makes in the total absence of LDL.

The only thing changing is the LDL in plasma. Golstein and Brown thus conclude that this defect provides "formal genetic proof that elevated LDL alone can produce atherosclerosis in humans."

But is this true?

Consider an analogy to a traffic jam. Two things happen:
  • The concentration of cars in the road increases.
  • The time it takes you to get home increases.
It is the same for LDL. The concentration increases, but so does the time it spends in the blood. Which determines the risk of heart disease?

In the late 1970s and early 1980s, it was discovered that LDL incubated with endothelial cells, the cells that line the inside of the artery, would over time become oxidized, due to the interaction between the PUFAs in its membranes and free radicals produced by the endothelial cells. Normal LDL would be taken up in small amounts by macrophages, but as soon as the macrophage obtained a little bit of cholesterol, it would shut off its LDL receptors and stop taking any more in. The "endothelial cell-modified LDL," however, would accumulate in macrophages unregulated. For a five-fold increase in the concentration of normal LDL, there would be absolutely no increase in the absolute amount of LDL taken up into the macrophage. For the same concentration, however, oxidized LDL would be taken up at five-fold the rate of normal LDL. Moreover, as higher and higher concentrations were reached, oxidized LDL would be taken up at higher and higher amounts, but normal LDL would not.

Obviously, these experiments showed that the concentration of normal (called "native") LDL could not affect the amount of LDL that macrophages would take up.

Later experiments, as described in my article linked to above, showed that it was oxidized derivatives of linoleic acid, mainly derived from dietary vegetable oils, that were the key constituents of the LDL particle that could turn on the genes in the macrophage that would cause it to turn into a foam cell.

It is these macrophages and foam cells that populate atherosclerotic plaques, initiating the inflammatory process, eventually degrading the fibrous cap and increasing the chances of rupture, and committing suicide, leaving cellular debris and large pools of oxidized lipid -- that is, a giant mess of toxic waste -- in the center of the plaque.

This evidence not only presents a problem for Goldstein and Brown, who argue that the concentration of LDL is the main determinant of heart disease risk, but also presents a problem for those who would argue that atherosclerotic plaque does not cause heart disease.

The "myogenic" theory promoted by Dr. Cowan is not necessarily at odds with the atherosclerotic-thrombotic theory promoted by the mainstream. Atherosclerotic plaque not only impedes oxygen delivery to heart tissue by occluding arteries, it also contains a mass of oxidized toxic waste. If it ruptures, and a clot doesn't form right away, then all that toxic waste would be free to wreak havoc on the oxygen-based metabolism of heart cells.

The obstacle to the myogenic theorists is this: if the LDL receptor activity exerts almost complete control over the risk of heart attacks, then any theory of how heart attacks happen must give a central role to the lipoproteins that interact with that receptor (this actually includes most lipoproteins, not just LDL).

So the question the myogenic theorists must answer is, what is the role of LDL or oxidized LDL in promoting capillary dysfunction or otherwise compromising the oxygen status of heart tissue, if not in promoting atherosclerosis, plaque rupture, and thrombosis?

Read more about the author, Chris Masterjohn, PhD, here.

Friday, March 20, 2009

Wherefore Art Thy Protection, O HDL?

by Chris Masterjohn

Hey everyone! It's great to be back. I got way behind with things after slipping and falling and dislocating my shoulder at the end of January, but I hope to be back to blogging regularly now.

Many of you may remember the drug torcetrapib, aimed at increasing HDL-cholesterol. It failed miserably, and killed a lot of people. Remarkably, there is a new drug, anacetrapib, aimed at doing the exact same thing, that is now going through the same trial process. Will it kill people?

An eight-week trial of under 600 people published in February found that anacetrapib had no more adverse effects than the placebo. This would be comforting, except that an eight-week trial of under 200 people published in 2006 found the exact same thing with torcetrapib, causing the lead author to publicly wonder, "Will torcetrapib be the next big thing in coronary heart disease risk reduction?" It was big, alright, but it didn't reduce any risks. A large-scale trial with over 15,000 people was stopped early at just over two years instead of more than 4.5 years because the drug was killing people. All-cause mortality was increased by 58 percent, representing an increase in cardiovascular deaths of 25 percent and a doubling of non-cardiovascular deaths.

These drugs are based on the reverse cholesterol transport theory, a theory that was tested for the first time in the torcetrapib trial and should have been at least tentatively rejected.

HDL binds to cells in the artery wall and takes up free cholesterol. It then esterifies the cholesterol, by which I mean it binds the cholesterol to a fatty acid, and moves it down into the core of the HDL particle. It can do two things with this cholesteryl ester. It can be taken up by the "LDL receptor" (the name is deceptive, I know) in the liver, thus delivering the cholesteryl ester to that organ, or it can deliver the cholesteryl ester directly to LDL. LDL, according to reverse cholesterol transport theorists, can deliver it to the liver too, but unfortunately can also deliver it right back into the artery wall.

What determines which action HDL takes? Cholesteryl ester transfer protein (CETP) facilitates an exchange between HDL and LDL (or especially VLDL, which is later transformed into LDL) wherein the HDL loses a cholesteryl ester and picks up a triglyceride.

Thus, let's block CETP! This is the reasoning of the drug manufactures. By blocking CETP, we lower LDL-cholesterol and boost HDL-cholesterol.

Epidemiological evidence suggests that the total-to-HDL cholesterol ratio, which is basically the same thing as the LDL-to-HDL cholesterol ratio, is the best blood lipid marker for heart disease. The word "marker" is key. Reverse cholesterol transport theorists assume this marker is causal. I believe it is a marker for the amount of time the LDL particle spends in the blood. If LDL receptor activity is low due to a) genetics, b) low thyroid status, or c) oxidative stress, LDL (or its VLDL precursor) will spend more time in the blood, interact more and more with CETP, and "steal" away cholesterol from HDL. LDL-cholesterol increases and HDL-cholesterol decreases. At the same time, it interacts with free radicals more and more, its limited supply of antioxidants runs out, the polyunsaturated fatty acids in its membrane oxidize, and it becomes atherogenic. This is causal.

How would reverse cholesterol transport theorists show that high HDL-cholesterol is causally protective? The perfect way to do this would be to use a drug that specifically boosts HDL-cholesterol and show that it reduces cardiovascular disease. The problem is that they just did this with torcetrapib and it increased cardiovascular disease. Reverse cholesterol transport theorists do not want to reject or modify their theory. They would prefer to believe there was something toxic about torcetrapib that had nothing to do with its CETP-blocking effects. There is one problem with this. In December, 2008, some scientists published a study finding no relationship between the degree to which torcetrapib boosted HDL-cholesterol and the change in the degree of atherosclerosis. They concluded the following:

The absence of an inverse relationship between high-density lipoprotein cholesterol [HDL-C] change and cIMT [carotid intima-media thickness, a measure of the degree of atheroslcerosis] progression suggests that torcetrapib-induced high-density lipoprotein cholesterol increase does not mediate atheroprotection [protection against atherosclerosis].

The medical field has created enormous confusion by conflating "HDL" with "HDL-cholesterol." When you go to the doctor and get bloodwork, they do not test your "LDL" and your "HDL." They test the amount of cholesterol contained in these lipoproteins. But they call your LDL-cholesterol your "LDL" and they call your "HDL-cholesterol" your "HDL."

When I say I do not believe that the epidemiological associations with HDL-cholesterol are causal, this does not mean that I do not believe that the HDL particle is protective. It is. But the evidence suggests that it is protective because of its highly specific role in delivering vitamin E to endothelial cells, not becuase of its role in reverse cholesterol transport. And guess what? CETP blockers directly undermine this process!

As Daniel Steinberg relates here and in his book, The Cholesterol Wars, researchers first discovered what came to be known as the oxidative modification of the LDL particle in 1979. When LDL was incubated for a long time with endothelial cells, the cells that line the inside of the blood vessel wall, something about it changed that made it toxic. Blood serum and HDL both prevented this change. In 1981, this "endothelial cell-modification" of LDL was shown to confer on the LDL particle the ability to be taken up by macrophages and transform those macrophages to the foam cells that populate atherosclerotic plaques. Further research showed that the polyunsaturated fatty acids in the membrane phospholipids of the LDL particle were oxidizing (going "rancid") during this modification, and that serum, HDL, or vitamin E could prevent the effect.

HDL is contained in serum and vitamin E is contained in HDL. This suggests that the protective effect of serum was largely due to its HDL content, and that the protective effect of HDL was largely due to its vitamin E content.

As it turns out, there is a very specific transport system designed to transfer vitamin E from the intestines and liver to endothelial cells, and it involves HDL. Vitamin E is originally released from the intestines into the lymph in chylomicrons, which then travel from the lymph into the blood. It is also recycled by the liver in the VLDL particle, which is the precursor to LDL. The liver secretes "nascent" HDL particles, meaning particles that have membrane proteins and phospholipids but not much of anything else. These HDL particles pick up vitamin E from the chylomicrons and the VLDL and LDL particles in the blood and then deliver it to endothelial cells.

HDL, as shown here, is three to five times more effective than LDL at delivering vitamin E to endothelial cells. LDL appears to deliver vitamin E to these cells simply by being taken up as a whole particle, whereas HDL interacts with what could be called the "HDL receptor" but is instead for the sake of confusing non-scientists called the scavenger receptor, class B, type I (SR-BI), and delivers vitamin E to the endothelial cell at between eight and twenty times the rate it is itself taken up by those same cells.

Once delivered to the endothelial cell, vitamin E not only prevents the oxidation of LDL particles as described above, but decreases the expression of "adhesion molecules" involved in the formation of atherosclerotic plaque, such as ICAM-1, VCAM-1, and E-selectin, and boosts the synthesis of nitric oxide, which protects against atherosclerosis at multiple levels. All of these actions have been attributed to the HDL particle, but since vitamin E accomplishes the exact same results, the actions of HDL appear to be attributable to its role in vitamin E transport.

Now how does HDL acquire the vitamin E from the other lipoproteins in the first place? One of the proteins involved appears to be... *drumroll*... CETP!

A test tube study published in May of last year found that a CETP-specific inhibitor decreased the transfer of vitamin E from other lipoproteins to HDL by 45 percent!

Perhaps torcetrapib killed people because of its "off-target toxicity." But why did its HDL-cholesterol-boosting effect fail to proportionally reduce atherosclerosis? Is it because the reverse cholesterol transport theory is wrong? If HDL's protective effect is due to its role in vitamin E transport, is it possible that CETP was killing people at least in part because it was undermining the transport of vitamin E from other lipoproteins to HDL, and thus undermining the delivery of vitamin E to the endothelial cells where it inhibits the oxidation of LDL, decreases adhesion molecule expression, and boosts nitric oxide synthesis, all the main components of the early atherosclerotic process?

If so, will large-scale long-term trials of the new CETP inhibitor anacetrapib show that this drug also kills people?

Read more about the author, Chris Masterjohn, PhD, here.