June 26, 2012

Cholesterol

The straight dope on cholesterol – Part VIII

by Peter Attia

Read Time 10 minutes

In this post we’ll double-click on a paper covering cholesterol and heart disease risk factors.

Last week the Journal of the American Medical Association (JAMA) published an article titled Lipid-Related Markers and Cardiovascular Disease Prediction, which you can download here.  This is quite timely as we are in the midst of our series on cholesterol and heart disease risk factors.

I was planning to write a post on my interpretation of this report, as I know many of you have questions about it, when I was reminded of one of my favorite principles in life: never be afraid to outsource to those more qualified.

While there are many folks more qualified than me to address this entire topic of cholesterol and heart disease risk, there are a handful who have always been very generous with their time and insights on this subject and who I consider mentors on this topic.  This list includes Drs. Tom Dayspring, Tara Dall, Allan Sniderman, and Jim Otvos.

Below are excerpts of comments from Drs. Dayspring and Dall, followed by the comments of Dr. Sniderman, with my comments interspersed for clarification.

 

Initial response by Drs. Dayspring and Dall

The authors from the The Emerging Risk Factors Collaboration (ERFC) conclude:

In a study of individuals without known cardiovascular disease (CVD), the addition of information on the combination of apolipoprotein B and A-I, lipoprotein(a), or lipoprotein associated phospholipase A2 (Lp-PLA2) mass to risk scores containing total cholesterol and HDL-C led to slight improvement in CVD prediction.

In other words, the authors concluded that advanced lipid testing, beyond “just” LDL-C, HDL-C, TG, and total cholesterol did little to help predict heart disease in people without a known history of heart disease.

The accompanying editorial by Dr. Scott Grundy (the former NCEP chairman) raises several flaws of the analysis including old apoB data where studies used primitive and non-standardized apoB assays as well as the use of out-dated older risk assessment tools established 20-30 years ago when cardiac disease manifestation and presentation were very different than today.

These analyses are flawed with respect to examining the atherogenic lipoprotein variables in patients in which cholesterol measurements and lipoprotein concentration measurements are not also examined in the patients where the variables are discordant. These measures (cholesterol concentrations and apoB) are correlated.  However, in the many patients where the measures are discordant, apoB and LDL-P are the proven better variables to measure both risk prediction and therapeutic goals. It is also unfortunate that this study provided no LDL-P analysis. Thus, these analyses might be of some interest to epidemiologists who look at entire populations, yet have little value to practicing clinicians who treat people one at a time.

It is difficult to make the case for apoA-I by itself in routine screening as it is not the most accurate way of quantifying total HDL-P. However both AMORIS (which somehow was not included in this analysis) and INTERHEART — two very large trials — revealed that the best risk predictor was the apoB/apoA-I ratio. So, in drug naive patients the ratio (which requires apoA-I measurement) is validated. No ratio is likely valid in patients on lipid modulating medications as drugs do not effect apoB and apoA-I equally nor do apoB and apoA-I have equal predictive abilities.

With respect to inflammation markers, such as highly sensitive C-reactive protein (hs-CRP), their appropriate use (as discussed in the recent NLA biomarker statement) is to be used not in place of lipid or lipoprotein concentrations but afterwards to better fine tune risk which several studies have shown they do. Their elevation, based on current knowledge, should lead the clinician to obtain more resolute lipid and lipoprotein goals of therapy, not per se any (still nonexistent) inflammatory goals of therapy. However, current studies do suggest further studies will be needed to show if it is important to also normalize at least some inflammatory markers.

The JAMA study states:

The addition of the combination apolipoprotein B and A-I, lipoprotein(a), or lipoprotein-associated phospholipaseA2 (Lp-PLA2) to risk scores containing total cholesterol and HDL-C provided slight improvement in CVD prediction.

When you apply that slight improvement to 300 million Americans you are talking about millions of persons who would indeed benefit.

Interestingly, last year the NLA reviewed all of these data, and much more, and came to the conclusion that apoB, LDL-P, Lp-PLA2 and Lp(a) were indeed useful in almost all folks who have greater than a 5% ten-year Framingham Risk score (most adults over 40 years of age).

Subsequent response by Drs. Dayspring and Dall

This study combined data from 37 prospective cohort studies where plasma apolipoprotein levels were measured at baseline in patients followed for an average of 10 years. They conducted 2 analyses:

  1. One which used apolipoprotein B (apoB), apolipoprotein A-I (apoA-I), lipoprotein(a) (Lp(a)), or Lp-PLA2 instead of total cholesterol (TC) and HDL cholesterol (HDL-C), and
  2. One using the alternative biomarkers in addition to TC and HDL-C.

They concluded that replacement of TC and HDL-C with apolipoproteins or their ratios was not associated with improved cardiovascular risk prediction, whereas adding lipoprotein factors to TC and HDL-C was associated with slight improvement in risk prediction.

Several previous epidemiologic studies have demonstrated that apolipoproteins, including apoB, may be as good as, and often better than, LDL-C , non-HDL-C and cholesterol ratios for estimating coronary heart disease (CHD) risk. In a previous meta-analysis assessing the association between baseline apoB levels and CHD risk from 19 prospective studies with follow-up of 9 years, apoB was a significant predictor of CHD, with an overall relative risk of about 2 (i.e., double the risk) for the upper tertile (i.e., upper third of the population) compared with the lower tertile.

Non-HDL-C has been suggested as a potential surrogate for apoB. However, while non-HDL-C and apoB are highly correlated they can also be discordant in many patients, including those with and without metabolic syndrome, as shown here and here.

Clinical trials showing that apoB was superior, even to non-HDL-C, in predicting risk for CHD are numerous, including AMORIS, Leiden Heart Study, AFCAPS/TexCAPS, LIPID, Health Professional Follow-up Study, NHANES, The Chinese Heart Study, Framingham Offspring Study, Cardiovascular Risk in Young Finns, INTERHEART, and IDEAL (summarized here).

Strong evidence now also exists that cardiovascular disease risk tracks with LDL-P/apoB (not LDL-C) in patients with discordant levels of these markers. Discordance analyses in the MESA study show that LDL-C over- or underestimated LDL-related risk in many patients, leading to suboptimal LDL management.  This recently published study in JAMA did not account for specific groups that were discordant but looked only at the population as a whole.  Remember physicians do not treat populations; they treat individual patients, one by one.

How can a physician know if a patient is discordant if they do not measure apoB or LDL-P?  To restate the point, another limitation of this study is that it did not include studies that used LDL-P analysis.

Most physicians view it as their goal not to miss one patient who could benefit from preventive therapies through lifestyle and counseling interventions or medications proven to reduce cardiovascular (CV) risk in the primary prevention setting.

Multiple organizations support the use of apoB level as both marker of CV risk and treatment goal. Current Canadian lipid guidelines have incorporated apoB as an alternate primary target of therapy due to the wealth of data supporting apoB in CV risk prediction. The American Diabetes Association and American College of Cardiology consensus statement in 2008 also recommended apoB as a target of therapy in those with high cardiometabolic risk.  Furthermore, as part of the comprehensive diabetes care treatment goals, the American Association of Clinical Endocrinology published recommendations for apoB as another target of therapy in addition to LDL-C, Non HDL-C, HDL-C and triglycerides.  The recommendations from AACC Lipoproteins and Vascular Diseases Division Working Group on Best Practices also list goals of therapy for apoB and LDL-P.

The JAMA study in question included studies from 1968 to 2007. ApoB assays have improved significantly over the years, as early assays were more primitive, non-standardized, and therefore less reliable. The study authors recognize this limitation in their comment section and it was also addressed in the accompanying editorial by Dr. Scott Grundy, the former NCEP chairman.  He highlighted several other flaws in the analysis including the use of out-dated risk assessment tools established 20-30 years ago when coronary artery disease presentation was very different to today. In addition, correct interpretation of the study findings is difficult without consideration of treatment differences among the patients included in the study (e.g., patients with multiple high risk markers may have been treated more aggressively, resulting in fewer events).

As a practicing physician, I have used apoB/LDL-P for more than a decade in order not to miss any patient that could be at risk and might benefit from preventive therapy.  I do not want any of my patients to become part of the national statistic:

50% of people with heart disease have normal traditional lipid values.

Population studies have diluted relevant clinical meaning to physicians treating individual patients. Clearly a better measure is needed to understand risk in individual patients. Randomized controlled clinical outcomes trials in children are rare, but does that mean we don’t treat children or young women?  ApoB and/or LDL–P can help physicians target which of those primary prevention patients need more aggressive lifestyle or medical therapy.

Conversely, it is also important not to over-treat patients with high cholesterol who in fact may not have apoB, LDL-P or lipoprotein (a)-related risk.  It may also not be cost-effective or even reasonable to treat such patients based on cholesterol levels. The key is early detection for effective prevention. After very careful review of all the published studies to date, the National Lipid Association’s published consensus on advanced biomarker testing in 2011 recommends that, except in the lowest risk patients, apoB and LDL-P should be considered in most patients for both risk assessment as well as ongoing clinical management.

On the other hand, apoA-I is minimally useful as a test in isolation as there is not a one-to-one relationship between each HDL particle and apoA-1 (as there is for an LDL particle and apoB). As there may be several apoA-I apolipoproteins on each HDL particle, measuring apoA-I alone will not accurately quantify HDL-P.  HDL is incredibly complex and the functionality of the HDL particle will likely be the focus of future assays and studies.  For example, the use of apoA-I as a tool to diagnosis familial hypoalphalipoproteinemia is very helpful.  This condition is very difficult to treat clinically but is an important secondary cause of low HDL-C that should be ruled out. Additionally, in both the INTERHEART and AMORIS studies the best predictor of cardiovascular risk was the apoB/apoA-I ratio.

Lipoprotein associated phospholipase A2 (Lp-PLA2) is an inflammatory marker, not intended for use as a “stand-alone” marker to assess cardiovascular risk, but in combination with other lipoprotein-based tools (e.g., apoB and LDL-P).   It is well recognized that inflammation plays a role in atherosclerosis.  Currently accepted methods of assessing inflammation such as high sensitivity C reactive protein (hs-CRP) may be elevated in many disease states including, but not limited to, vascular disease. Furthermore, hs-CRP levels may also fluctuate greatly so multiple measurements are typically required.  I have always considered Lp-PLA2 to be a superior marker of vascular disease or what I consider “angry arteries.”  When Lp-PLA2 is elevated, treatments aimed at reducing inflammation (e.g., dietary modification, omega-3 fatty acid supplementation, smoking cessation) become important.  Clinically, high levels of Lp-PLA2 indicate that the disease process has not been effectively halted — arterial plaque may still be actively forming — and more aggressive treatment is required as unstable plaque may be present. Lp-PLA2 is not meant to be used as a marker in isolation or to replace other traditional methods of risk assessment.  However, it greatly augments the utility of the latter, and is a very useful tool to guide us in ongoing treatment decisions.

Until levels of a patient’s biomarkers lie within the optimal range, it is not clear that their risk has been eliminated.   If our goal is to reduce the epidemics of cardiovascular disease and diabetes, we need to be aware of the role lipoproteins play in cardiovascular and diabetes disease prediction and continue to carry out research to find better ways of detecting disease at earlier and earlier stages.

Additional commentary by Dr. Sniderman

In the JAMA study the average non-HDL-C was 175 mg/dl, which is the 82nd percentile of the U.S. population whereas the average apoB was 110 mg/dl, which is the 67th percentile. They should match, but they do not. Obviously, some populations have higher non-HDL-C than Americans. The Swedes, for example, certainly do. But the Swedes have higher apoB levels to match.  No population that I have ever seen has values this discordant, which means their lipoprotein composition is different from any I have ever seen.  This raises the question as to how accurately apoB was measured. From Table 1, of the 26 studies with data on apoB, blood was collected in 1 starting in 1968, in 1 in 1970, in 9 in the 1980’s, in 8 in the early 1990’s.

When were the apoB’s measured in relation to when they were obtained?  We don’t know.  Reading the original papers, in the great majority, measuring apoB was not part of the protocol.  For 13 of the studies, no methods are listed and another 5 are listed as in-house assays (i.e., non-standardized). None of these can have standardized results. Nor are they necessarily accurate. Even the studies employing commercial assays were not necessarily standardized.  The actual average values for apoB are listed in Table 1 and, not surprisingly, they are extraordinarily variable. These are mainly European studies and the average apoB ranges from 0.86 to 1.33 with many of values in the 1.0 to 1.2 range. This variance exceeds anything I have ever seen and anything that I think is epidemiologically possible.

The trends can be compared within studies but the problem is that this is a patient level study, which means all of these different results from all of these different assays are mixed together. How do you mix apples and oranges and nuts and pineapples and pretend they are all cherries? Obviously, you can’t. If you did not measure something accurately, if the results from the different studies differ so radically, how can they be lumped together?

What ERFC claims is the strength of their study is actually its weakness.  Our meta-analysis was done at the study level. All the studies in our meta-analysis were published and therefore all the methods to measure apoB are listed. There are two sources of assay error: imprecision (lack of reproducibility) and inaccuracy (lack of standardization). Study level analyses are certainly affected by imprecision but not so much by inaccuracy since the trends in each study are what is quantitated. This means our design, in this instance, is stronger than their design.

The irony of this analysis is that the assays for apoB have been standardized and are precise accurate but require the use of a standardized assay. LDL-C has not been standardized and the errors in measuring LDL-C are much more substantial than the errors in measuring apoB. ApoB is measured much more accurately and precisely in clinical practice today than it was measured in the research studies in ERFC. ApoB was evaluated in this study based on methods that no one would use today.

If one accepts ERFC, then total cholesterol is just as good as LDL-C, non-HDL-C and apoB.  This is not a reasonable conclusion. What does this imply about the studies that showed LDL-C was better than total cholesterol (TC) and the studies that showed non-HDL-C was better than LDL-C and the studies that showed apoB was better than LDL-C and non-HDL-C?  It’s hard to imagine, based on the conclusions of the ERFC, that we should go back to using TC as the screening tool for CV risk.

On page 2501, ERFC writes: “replacement of information on total cholesterol (TC) and HDL-C with apolipoprotein B and A-I significantly worsened risk discrimination and risk classification.”  However, look at Figure 1. What happens when TC and HDL-C are replaced by the TC/HDL-C ratio? Taking out the numerator (TC) and the denominator (HDL-C) and putting in the ratio (TC/HDL-C) is the worst thing one can do. The c-index change is -0.0098 — more than three times worse than with apoB, and net reclassification is much worse also. How can the way the same numbers are entered make such a difference?

The current study published in JAMA does not create a compelling case to abandon the use of advanced lipid testing in favor of standard testing.  It suffers from many methodological flaws and, upon careful examination in the context of the entire body of literature, actually reinforces the need for lipoprotein testing in all but a select few patients.

Photo by Joshua McKenty is licensed under CC by 2.0

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  1. Hi Dr. A. – I’ve been reading your site for a few months and I have to say that I just can’t express how appreciative I am of the information you are presenting. It is so very difficult to find a doctor who understands even a fraction of the relationship between diet, lipids and insulin. They’re all just so stuck in the ‘low-fat, high fiber’ mantra that it makes me want to scream. Thankfully, at least I have a doctor who will listen to me, even if he thinks I’m crazy. The problem is that I get little feedback and I’m doing all my own research. So, if I run into a problem, I’m literally on my own. He’ll support me with what I am doing, but when things come up hinky, his only advice is to fall back on what HE knows and believes – which is, low fat/high fiber, take some pills.

    I have had severe hormonal problems all my life (PCOS, endometriosis and growth hormone deficiency). Needless to say, these things came with the obvious result: insulin resistance. Two years ago I had a complete hysterectomy, which threw me into menopause early. Well, this doesn’t quite ‘cure’ insulin resistance. Although it changes it somewhat. Ever since I discovered that it was sugar consumption that was the culprit and not fat, I have been conscientious about carbohydrate intake. This at least kept me from ballooning up to monstrous proportions. About a year before I had my surgery, I did the basic Atkins program to much success. I dropped all the weight very quickly that I’d piled on over multiple years and went into my surgery feeling pretty good. Post surgery, I was more on a ‘maintenance’ program than anything, but carbs found their way back into my diet. It was not long before I was putting on weight at an alarming rate. I was also feeling horrible, and not just from the weight gain. It was about this time that I started HRT (bio-identical estrogen and progesterone). This seemed to not only make me feel a whole lot better, but stabilized the weight gain. This was also when I started researching the science behind Atkins and low carb eating, as well as the dangers of grains. (I have listened to/watched/read Dr. Noakes, Dr. Kendrick as well as Gary Naughton.) I went full steam into a very strict high fat, moderate protein, less than 20 grams of carbohydrates per day. Well, the first week, I had pretty much a repeat of my experience on Atkins the couple years prior. I lost about 5 pounds. After that, it stalled entirely. I actually managed to reduce carb intake to 10 or less and was able to lose about a pound a week. This was rather depressing and I couldn’t figure out why my experience was so different. After more research, my conclusion was the that the major change in hormones was the glaring thing that was different. Despite HRT, I’m just not going to have the same hormonal makeup that I did before (not that it was optimal then; it was pretty screwed up), but now I make none of my own sex hormones. So, I diligently kept at it and got down to within 10 pounds of where I’d like to be and here I sit. That’s my first dilemma. I just don’t know what else I can do at this point.

    I could live with this….but….a recent routine blood panel showed some pretty glaring problems. First of all my blood pressure all of my life has been low. So low, that it is usually a major endeavor to draw blood from me. It was usually 115-117//72-75. Now it’s 128/85. That’s a big jump for me. Secondly, my cholesterol nearly made my doctor faint. TC was 290; HDL 88; LDL 186; TG 78. Well, I managed to calm him down after I did the calculations for the ratios and told him that TC/HDL was optimal; HDL/LDL was optimal and TG/HDL was also optimal. He wasn’t all that convinced I wasn’t going to have a massive coronary. So, I told him that if it would make him feel better, I’d go for the VAP. Which I did. The problem is that he’s completely unfamiliar with the results of that test and what they all mean. I’m not well-versed enough to understand it all either, but there were some changes of note and the tests were only done 3 weeks apart (with no changes in diet). They were done at different labs, but this time my TC was 212; HDL 85; LDL 178; TG 92. My apoB100- calc was 141 which is flagged as high and my Lp(a) was given as 16.0 (also high). I’m solidly a pattern A with LDL1 46.0; LDL2 91.2; LDL3 39.8 and LDL4 0.9. So, clearly I understand the large particle composition is the majority and a good thing. The problem I’m having understanding is the apoB100 seems to indicate that I have an excessive number of particles?

    I know labs can vary, but there seems to be some marked changes. I have not changed my diet. I am still under 20 grams of carbs per day. I eat when I’m hungry. I am fastidious about consuming no grains whatsoever as part of my daily carb intake. My carb intake is usually in the form of strawberries or blueberries. Otherwise, it’s all kinds of meats, various fish, eggs, cheese, whipped cream (for the berries), whole cream in my daily cup of coffee, and my handful of cashews or almonds every other day or so. I do drink a diet pop once a day, and we make it here at home with filtered water, our own carbonation and flavoring sweetened with Splenda with no other additives. I just can’t figure out why my lipid profile isn’t better. I also can’t figure out why I can’t get rid of the last extra 10 pounds. I don’t feel badly….I actually feel pretty good, but as I’m sure you know, that doesn’t mean something bad isn’t going on. I just wish I could figure out what it is. Can you possibly steer me in the wright direction?

  2. Woops – I just want to say that I made a typo in the transcription of my 2nd cholesterol test. {{They were done at different labs, but this time my TC was 212; HDL 85; LDL 178; TG 92.}} TC should be 312 NOT 212. So, this is UP from the first test where TC was 290.

    • Interesting…certainly violates Occam’s Razor in an amazing way. Not sure I buy it, but never bad to have a hypothesis out there. Does this hypothesis, if true, change the treatment or risk mitigation?

  3. Sorry if I missed this. Are there any drugs that are being developed–or that already exist–that upregulate the production of sterol efflux transporters in macrophages?

    Thanks,
    Nick

  4. I have been reading just about anything I can get my hands on about cholesterol and it has been making me rethink my own situation. Quick overview – my dad had CAD, had bypass surgery many years ago. So I’ve always had the “family history” I have been on a statin for x2 years slowly weaning it almost as soon as I was on it as well as making changes in my diet. Presently I am on a successful ketogenic diet x 7 mths and my HDL/trig ratio and HDL/chol ratio are both good. My next step is to completely stop the remaining small dose of statin and retest again as well as do the NMR Lipo Profile. My question to you is how long should I be off the statin prior to doing the NMR testing. Is there an optimal period for my body to recover and continue with it’s own natural making of cholesterol so I can get an accurate test?

  5. Hello Dr. Attia.
    I know I’m reviving an old blog, I feel you wont mind, because of your desperate need to spread all your insights on the old understandings of cholesterol as it relates to heart disease. I feel inclined to pick your brain, simple because I admire your incredible knowledge, and respect your efforts to actually put any effort into explaining. I myself am a dedicated researcher, have no scientific nor medical background, but I hope to learn from talented people like yourself. In the hopes to provide such services like you do and other great people, by becoming an expert in areas the interest me.
    My questions:
    1. Having elevated LDL-P, but low ox-LDL, does their risk lower than someone with elevated LDL-P and ox-LDL?
    2. Does reverse cholesterol transport happen by LDL-P transferring cholesterol onto HDL-P?I know you wrote that HDL-P transfers cholesterol to LDL-p. Do both have same united responsibilities? It seems to me both have the same actions in lipidation and dislipidation, however APO-B LDL are rebellious, and for that reason tend to get internalized by LDL-R on endothelium cells, while HDL has no role. As the concentration gradient of LDL-P increase in plasma so does the rate of foam laden macrophage, free radical oxidation, and glycation. Once the permeability happens the rate of penetration of LDL-P increases continuously.
    3. I know you have not mentioned much on phytosterols, can you provide some information on it? I read that unesterfied sterols are not able to become esterified, therefore ANY particles carrying the phytosterols will become oxidized. Any truth to this? Can a dysfunction occur with acetyl-coA cholesterol acetyltransferase in the liver, which increases the risks of all particles to become oxidized?
    4. Lastly, how does a smaller HDL-P provide more benefits than a larger HDL-P? From what I gather and understand is the smaller particle will carry more triglycerides than cholesterol, which will deliver more cholesterol into fat cells hence overall improving TG serum concentration? My understandings on when your loosing weight, your not only shrinking fat cells directly, but also refilling fat cells by the actions of particles, and eventually continuing the fat loss process. Meaning, your lowering TG in plasma, by dislipidation and eventually those transported triglycerides will refill fat cell and eventual undergo lipolysis too. That is how TG serum concentration drops. Is this a possibility of the many you state why small HDL particles are beneficial? I believe this will lower LDL-P count because more cholesterol can be shipped by HDL-P, resulting in lower requirement for LDL-P. All complete hypothesis/speculation on my part.

    I hope you have the time to answer me, and I wish you can continue with this cholesterol blog! Hopefully I can revive your interests, to continue blogging/writing on cholesterol.
    Can you provide me with any books/articles/studies/people that I should look into, towards my continuous need to perfect my understandings on cholesterol? I also have huge interests in insulin, brain: food/reward, fat cells, various dieting strategies/pathways involved, etc.
    Thank You Dr. Attia,
    Misha

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