Monday, August 31, 2009

Cholesterol Clues - What those confusing cholesterol numbers really mean

by Kalia Doner

YOU MAY NOT REALIZE IT, but your every breath depends in part on a pale-yellow waxy substance that's a building block of cell walls, sex hormones, the brain and even the juices that digest fat in the gut.

Exactly what is this oh-so-essential element? It's cholesterol, a fat-like product of the liver and intestines that moves through the bloodstream to every organ in the body. Cells extract cholesterol from the blood as they need it, and, if there's any extra floating around, the liver helps the body excrete it.

What's the Worry?

Despite the importance of cholesterol to all the body's systems, we are constantly told we should be concerned about it. So, if that seems confusing, here's the scoop.

It turns out that our body makes all the cholesterol we need to be healthy, but we end up with far too much in our bloodstream because our diet is overloaded with saturated and trans fats — found in meat, dairy and some prepared foods — and the liver turns that excess fat into excess cholesterol. (We also take in cholesterol itself from foods such as eggs, but high blood levels are mostly a result of eating an excess of the wrong kinds of fats, not dietary cholesterol.) Once cholesterol is ready to be sent into the bloodstream, it needs to hook up with a fat-transporting protein. The protein that most often becomes its partner is called LDL (low-density lipo-protein). The more harmful the fats we take in, the more cholesterol is produced and the more LDL arrives to transport it.

When there are too many of these packages of cholesterol and LDL, they can get hung up along the lining of the blood vessels. This can result in the formation of plaques that constrict blood flow and permeate the vessel walls, stiffening them so they can't respond to stresses appropriately. The consequences may be devastating: stroke, peripheral artery disease and heart attack.

Alphabet Soup
If you are one of the 99 million adult Americans who have been told they have "high total cholesterol," you are at increased risk of heart disease. If your number is 200 to 239mg/dl, you are at a borderline high-risk level; a level of 240 or higher means you are more than twice as likely to develop heart disease as someone whose cholesterol level is below 200.

But knowing your total cholesterol number is not as helpful in predicting your risk of cardiovascular disease as knowing the particular subsets of total cholesterol: your LDL level; the level of another lipoprotein called HDL (high-density lipoprotein), which helps shuttle cholesterol out of the body; and the level of a blood fat called triglyceride.

Unfortunately, elevated LDL and triglyceride levels don't usually cause symptoms, so you may not be able to tell that you are at risk for heart disease without a blood test.

That's why the Third Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (ATP III) recommends that at least once every five years, adults age 20 or older have a complete lipid profile that measures total cholesterol, LDL, HDL and triglyceride levels.

LDL lowdown
When it comes to coronary heart disease, LDL appears to be the main culprit, since it can damage vessel walls.

"Studies have clearly shown that the more intensive the approach to lowering LDL, the more effectively you prevent heart attacks and other problems," says Steven Nissen, M.D., chairman of the department of cardiovascular medicine at the Cleveland Clinic in Cleveland. "You want to use lifestyle modifications that include stopping smoking, improving nutrition and increasing physical activity, along with intensive drug therapy."

An LDL of 130 to160mg/dl and above indicates an increased risk of heart disease. But if you have already been diagnosed with heart disease, your LDL cholesterol should be less than 100, and your doctor may even set your goal at lower than 70.

Tricky triglycerides
If we take in more calories than we need to run our body, the excess is turned into triglycerides and stored in fat cells for later use. If you consistently eat more calories than your body needs, your triglyceride level may be high. That's the case for around one-third of adults in the U.S., who have levels of 150 or higher, according to a study in the Archives of Internal Medicine.

The National Institutes of Health guidelines for triglycerides levels are: Normal is lower than 150mg/dl; borderline high, 150 to 199; high, 200 to 499; very high, 500 or higher.

Healthy HDL
These lipoproteins are used for reverse cholesterol transport, carrying it from other parts of the body back to the liver and out of the body. HDL helps keep cholesterol from building up in the walls of the arteries and acts as an anti-inflammatory that reduces the likelihood of clots and dilates the blood vessels.

According to the National Cholesterol Education Program (NCEP), you should know the risks associated with various HDL levels: Less than 40 mg/dl creates a major risk factor for heart disease, 40 to 59 is a healthier level, and 60 and higher is considered more protective against coronary heart disease.

What is Non-HDL Cholesterol?
This new category of cholesterol measure¬ment was introduced in ATP III and is believed by many doctors to be an important number for people with elevated triglycerides and diabetes. It combines information about triglyceride levels with information on a form of LDL called very-low-density lipoprotein (VLDL). To determine your non-HDL level, you subtract your HDL number from your total cholesterol. Non-HDL levels should be 30mg/dl above a person's LDL goals.

Med Smarts
The medications that lower total and LDL cholesterol as well as triglycerides include statins, bile acid sequestrants, niacin (nicotinic acid) and fibric acids.

Statins can lower LDL 18 to 55 percent, raise HDL 5 to 15 percent and lower triglyceride levels 7 to 30 percent. But "statins' side effects are dose-related," says Cleveland's Dr. Nissen, "so you want to use them as judiciously as possible."

Bile acid sequestrants can lower LDL 15 to 30 percent and raise HDL 3 to 5 percent, but have no effect on triglyceride levels.

Niacin (nicotinic acid), a B vitamin in prescription doses, can lower LDL 5 to 25 percent, raise HDL 15 to 35 percent and lower triglycerides 20 to 50 percent.

Fibric acids can lower LDL 5 to 20 percent, raise HDL 10 to 20 percent and lower triglycerides 20 to 50 percent.

Going Lower
Bringing down your elevated cholesterol levels is a matter of finding the right balance between therapeutic lifestyle changes and medication. "If your LDL level is above your goal, you want to talk with your doctor about lowering it' says Scott M. Grundy, M.D., Ph.D., former chairman of the panel that produced ATP III and currently professor of internal medicine at the University of Texas Southwestern Medical Center in Dallas. "How you do that is secondary to getting it done. But you do want to do it with minimum side effects and cost effectively."

Lifestyle steps
TLC dietary recommendations in APT III include making sure that your daily fat intake adds up to no more than 25 to 35 percent of total calories: 7 percent or less from saturated fat, 10 percent from polyunsaturated fat, up to 20 percent from monounsaturated fats. Carbohydrates (mainly from grains —especially whole grains—fruits and vegetables) should make up 50 to 60 percent of total calories; fiber, 20 to 30 grams a day; protein, less than 15 per¬cent of total calories; and cholesterol, less than 200mg a day.

"In addition," says Dr. Grundy, "weight management and increased physical activity are recommended." However, it is difficult for many people to stay on a TLC program. "Lifestyle changes, combined with managing individual risk factors, are vitally important in terms of initial therapy," says C. Noel Bairey Merz, M.D, director of the Cedars-Sinai Women's Heart Center in Los Angeles. "Regrettably, many patients find it difficult to permanently alter their lifestyle or to follow through on risk-management recommendations. While therapeutic lifestyle changes have a large role in heart health and work well when the recommendations are carefully followed, the role of oral medications is also important—especially because most people are better at taking pills than making lasting life-style adjustments."

The Damage It Can Do
We constantly hear about the relationship of high cholesterol to heart disease — after all, heart attacks (triggered by cholesterol-blocked arteries) cause around a half million deaths a year. But the consequences of elevated cholesterol levels are more far-reaching than that, contributing to significant damage of other organ systems.

Cholesterol and the Brain
There is mounting evidence that chronically high cholesterol levels alter brain function. Not only can they reduce blood flow and oxygen to the brain, they may actually contribute to the formation of the tangles in the brain — caused by a protein, beta-amyloid—that characterize Alzheimer's disease. One study in the Archives of Neurology found that among the women studied, "the higher LDL and total cholesterol they had, the worse they did on cognitive testing.” These findings are echoed by Yaakov Stern, Ph.D., a professor at the Taub Institute for Research on Alzheimer's Disease and the Aging Brain at Columbia University Medical Center in New York City. His research over the past decade has also demonstrated that those with a history of diabetes and higher cholesterol levels experience faster cognitive decline as they age. Unfortunately the dream that taking cholesterol-lowering statins may help the elderly with high cholesterol stave off dementia or Alzheimer's seems unfounded. A Cochrane Library review of two studies that looked at more than 26,000 people found there was no benefit.

Cholesterol and Kidneys
Researchers have long known that diabetes and high blood pressure are risk factors for kidney disease. But in the past five years or so they have identified the risks to the kidneys that elevated total cholesterol, low HDL levels, and high levels of LDL and triglycerides pose. A study in the Journal of the American Society of Nephrology found that men with total cholesterol above 240 were particularly vulnerable. And, according to study author Tobias Kurth, M.D., and his colleagues, "men with HDL cholesterol below 40mg/dl, those with elevated non-HDL cholesterol or an elevated cholesterol/HDL ratio had double the risk of kidney disease."

2 comments:

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