July 31, 2009

Apolipoprotein- B But not LDL Cholesterol Linked to Artery Calcium Build Up

Many of my readers know that despite their doctors' obsession with their Cholesterol levels the evidence has never supported the idea that cholesterol levels predict heart attack. You can read about this issue, with resarch citations, on this page: A1c And Post-Meal Blood Sugar Predict Heart Attack or if you are looking for total immersion in the research regarding cholesterol and cardiovascular disease you can get it from reading Gary Taubes' monumental book, Good Calories, Bad Calories.

But because people with diabetes do get heart attacks at a rate higher than the general population, it would be nice to know what markers could be trusted to help you know your real risk.

Your A1c and, even more strongly, your post-meal blood sugar levels are helpful in assessing risk. But some people with well controlled blood sugars do develop heart disease. So some recent research published in the journal Diabetes might point to another safe tool you can use to assess your own, personal risk.

You can read the abstract of the study here:

Apolipoprotein B but not LDL Cholesterol Is Associated With Coronary Artery Calcification in Type 2 Diabetic Whites Seth S. Martin et al. Diabetes. Diabetes August 2009 vol. 58 no. 8 1887-1892 doi: 10.2337/db08-1794

Apolipoproteins are proteins that are produced in the intestines and liver. They attach to cholesterol particles released by digestion and are what allow these particles to be transported through the body. Because apolipoproteuns fit receptors on various cells, they play a large part in the processes that allow cholesterol to be metabolized.

Apolipoprotein B (APO B) is the lipoprotein that attaches to LDL cholesterol and helps transport it around the body. It has long been known that it provides a better measure of cardiac risk than does the measurement of LDL cholesterol. This is not news. You can read about that in a study published in 2002:

How, when, and why to use apolipoprotein B in clinical practice. Sniderman Allan D. The American journal of cardiology, ISSN 0002-9149 2002, vol. 90, no 8A (86 p.) (32 ref.), pp. 48i-54i

The reason APO B is useful is so useful is that there is one molecule of APO B associated with every particle of LDL cholesterol. This means that the measurement of APO B points the the actual number of LDL particles. This is especially important because The usual LDL measure you get on your lab report does not. In fact, the LDL value on your cholesterol test result isn't an actual measure of your LDL. It is a calculated number that is derived by applying a simplistic formula to the triglycerides and total Cholesterol that were measured. Because it is a calculation, not a measurement, it can give either erroneously low or erroneously high readings depending on the size of your LDL particles.

Dangerous LDL comes in small particles which are prone to attach to arteries. Very large fluffy LDL molecule tends not to bond to your arteries. The LDL calculation apparently gives something like the total volume of your LDL, so if, like me, you have a modest number of very large fluffy molecules the formula gives an extremely high LDL figure while someone with a lot of very small dense LDL may be told they have a low, misleadingly comforting LDL number.

This is one reason why fully one half of people who have heart attacks have "normal" cholesterol--because just measuring the amount of cholesterol is worthless. You have to know how many cholesterol particles you have to better understand risk since small dense LDL does correlate with your risk of having cholesterol clog your arteries.

So while it isn't new that your APO B value is a useful indicator of risk, the new Diabetes study is useful because it finds that APO B is the only LDL test result that provides useful information to people with Type 2 diabetes.

This may be because most people with diabetes have extremely high triglicerides which skew the LDL calculation. If you have normalized your blood sugar this may mean that the APO B test is not quite as useful for you.

The other reason that the APO B test might be more useful for people with diabetes is that they are usually put on statins which can cut down on the amount of LDL they secrete without changing the characteristics of those LDL particles. So while LDL may drop after taking a statin, the person may still be making a lot of very tiny, dense LDL molecules that give them a heightened risk of clogged arteries, even though their LDL numbers went down.

Reading this study, you might ask yourself, "Why not just get a CAC scan, as Dr. Davis of the Heart Scan Blog suggests. The answer is that the CAC is expensive and may not be covered by insurance. In addition, depending on who offers it, it may expose you to significant amounts of radiation. Dr. Davis points out this doesn't have to be the case, but in practice you may not have the expertise to know if the CAC scanning available to you is being done with low radiation equipment or not, and sadly, you can't trust the people doing the test to give you a trustworthy answer because they have a strong financial interest in selling you the scan.

So if you have a high risk of heart attack and are trying to decide if a heart scan would be worth the money and the radiation exposure, you might consider asking your doctor to do the APO B test to help you get a better feel for whether the scan would provide useful information. If the APO B number is high, it is more likely you would see evidence of significant calcification in your arteries. If you need to see the picture to get motivated to do something about this issue, the scan might be worthwhile.

But this raises an important issue. Medical testing is a waste of money unless result A will lead to your adopting a different treatment than result B. It should never be done just to satisfy your curiosity.

If you believe you have a higher risk of heart attack than a normal person you may already be doing all the things people can do: cutting way down on carbs, monitoring your blood sugar and aiming for the lowest possible A1c, keeping your blood pressure normal, supplementing with Vitamin D, and exercising. If you have had your C-reactive protein measured and it was high, you may already be on a statin.

So before you invest in further cardiac testing you have to ask yourself, "What will I do if the test comes back with a value suggesting I am developing heart disease?"

The answer may be, become obsessive and depressed about health in a way that does not improve the quality of your life and this is the last thing that you want. You can live every day of the next 30 years waiting for your heart attack, or you can do what you can do and extract the maximum pleasure out of today and the days that follow it. My dad lived for 30 years after a diagnosis of "severe heart disease." He did end up having a heart attack--28 years after his diagnosis, at the age of 98. He died of a fall two years later. He led an active life for those last 30 years and would have been far better off without the diagnosis since he spent 28 years waiting for that heart attack--and threatening to have it any time anyone in the family disagreed with him!

Heart disease is a valid concern for people with diabetes, but I hear from far too many recently diagnosed people who are terrified that their diabetes diagnosis is a death sentence. It isn't-if you keep your blood sugar under control.

As I have mentioned in an earlier blog post, researchers are seeing far fewer heart attacks than expected in large scale studies. Many reports about cardiovascular disease use the "risk" statistic, which produces a big, scary number rather than the incidence per 1000 people number which gives a much smaller, more reasonable number.

So if you are already taking the steps a prudent person would take, there probably is no point in pursuing ever more diagnostic tests. If the tests could make a difference in your treatment plan--for example, convince you to take an expensive, side-effect rich statin--they might be worth consideration.

To summarize data I have discussed on the main Blood Sugar 101 web sit, here are the test results most indicative of cardiovascular health:

1. Triglyceride levels. Under 150 is the minimum, much lower is much better. Triglycerides should come down as you cut your carbohydrate levels because triglycerides are the product of the digestion of carbohydrate. If they don't come down with low carb dieting and tight blood sugar control, you should have your doctor explore why.

2. Blood pressure. Keep it under 140/85 and demand aggressive therapy from your doctor if it stays higher for any period of time.

3. Cardiac Specific C-Reactive Protein. High levels point to inflammation in your arteries and suggest you might be one of the people who would benefit from taking a statin.

4. Apo B which can help you interpret your LDL score.

5. LDL particle size is a helpful test since LDL particle size appears to be a very good indicator of whether your LDL will caused clogged arteries but very few doctors will perform it or have even heard about it.

6. EKG to determine if you have had a silent heart attack in the past.

6 comments:

Ryan Lanham said...

What does one do with silent heart attack info assuming one is doing all that is possible for the other risk factors? I mean, really, a particular EKG doesn't lead to a different treatment set. It may lead to a stress test, but then what?

Jim Purdy said...

An imaginary Red Lobster restaurant conversation:

ME: Waiter, I'm thinking about ordering your Red Lobster Crispy Calamari and Vegetables, but it has a whopping 1520 calories and 116 grams of carbohydrates. What will that do to my Apolipoprotein B?

WAITER: Uh, excuse me sir?

ME: You know, Jenny talks about that in her Diabetes Update blog. And what about the impact on my Cardiac Specific C-Reactive Protein?

WAITER: Who's Jenny?

ME: Surely you know Jenny, the anti-Roche crusader.

MANAGER: Sir, we don't have roaches at Red Lobster. I'm going to have to ask you to leave and never return.

Jenny said...

Jim,

THAT was very funny. Thanks.

trinkwasser said...

Gosh I'm jealous of you Yanks, you can get all these sophisticated tests! Here in the UK we get TChol to check for Statin Deficiency and that's your lot. When I asked for an A1c and Full Lipid Panel it was cancelled by the receptionist.

Seriously though, William Davis is a major source of information on such things and their relationship to cardiovascular risk.

Someone reported recently that their doctor's access to his blog was blocked, so he must be doing something right.

Jenny said...

The trade off is that if you lose your job and have an accident, you don't end up getting charged $1100 for a 3 minute talk with a doctor who doesn't do anything and an x-ray.

Even if you paid for your own tests via a private clinic, you'd still come out WAY ahead. And many doctors here won't do the extra tests either, even though we pay through the nose for the insurance. That's because some doctors get paid extra by insurance companies for NOT ordering tests etc the insurer has to pay for.

Nasty, nasty system. I'd rather have yours and pay for the extras if I had to. As it is I pay over $6,000 a year for insurance and have to pay for quite a lot anyway and FIGHT for the rest.

trinkwasser said...

Yes both our systems have their advantages and their disadvantages. The downer is that they are both converging onto the worst of both possible worlds. :(