Heart Disease, Artery Damage and PCBs
| More than 50 research studies involving human studies
and heart disease are cited in this report. They indicate a link
between PCB exposure and atherosclerosis (coronary artery disease)
which is a leading cause of coronary heart attacks, strokes and
aneurysms. Several studies show PCBs raise or alter blood levels
of cholesterol, triglycerides, lipoproteins, and other blood chemicals
considered serious risk factors for atherosclerosis.
Several mechanisms for arterial damage are described in
the studies. More than 100 additional animal studies confirm these results
and provide more information.
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A team of researchers at the University of Kentucky has found that Vitamin E can protect the lining of blood vessels against attack from PCBs (source: R.M. Slim et al., "Antioxidant protection against PCB-mediated endothelial cell activation," Toxicological Science, in press). One of the researchers, Dr. Bernhard Hennig stated, "Some outreach programs might suggest that people who are at risk take supplements of antioxidants to make them less susceptible to PCB-mediated toxicity. It's unbelievable how potently Vitamin E protects." Another professor of toxicology, Larry Robertson, added, "PCBs are constantly moving from blood or fat," he notes. Furthermore, Hennig and his colleagues reported earlier this year that a high-fat diet can increase the endothelial damage caused by PCBs (source: B. Hennig et al., "Linoleic acid amplifies polychlorinated biphenyl-mediated dysfunction of endothelial cells," Journal of Biochemical and Molecular Toxicology, 13[2]:83-91, 1999).
Why haven't we heard anything about this research in Northeast Wisconsin? Heart disease is affecting many people in our area, and widespread PCB contamination may be a contributing factor. The public should be informed.
Atherosclerosis --- This type
of arteriosclerosis forms deposits of yellowing plaques containing cholesterol
and other lipids in arteries, leading to "hardening of the arteries." Atherosclerotic
coronary artery disease is the underlying cause of most ischemic cardiac
events and can result in myocardial infarction, congestive heart failure,
peripheral vascular disease, cardiac arrhythmias, and sudden cardiac death.
| In a normal artery its endothelial lining allows smooth passage of blood and acts as a protective cover against harmful substances circulating in the bloodstream. The endothelial lining is surrounded by a sheath of muscle cells. In the earliest stage of atherosclerosis fatty streaks form on the lining. The lesions are widely scattered at first, but as the disease progresses they become more numerous and can eventually cover the entire inner surface. Later, atheromas of newly formed muscle cells filled with cholesterol and other lipids build up and protrude into the vessel. These deposits cause the inner wall to become roughened and also cause the muscle wall to be rigid and inelastic. |  |
Narrowing of the diameter of the artery and hardening of the muscle wall decrease blood flow through the vessel and may lead to death of the tissues served by the vessel. The body forms calcium to wall off the inflamed areas in the artery. This brittle, calcified area can be sheared off as blood flows through the artery, resulting in injury and formation of a blood clot (thrombus). A clot that forms in the region of this plaque can block the flow of blood to part of the heart muscle and cause a heart attack. If a clot blocks the flow of blood to part of the brain, the result is a stroke. The process also damages and deforms the muscle wall to the extent that it becomes weakened and may develop an aneurysm.
The exact cause of atherosclerosis is unknown and is most likely a combination of factors, including high blood pressure (hypertension), heredity, age, obesity, and smoking. Women’s risks are lower until after menopause. Diabetics are especially susceptible and tend to develop atherosclerosis earlier in life. (See Diabetes and PCBs)
Lipids --- Lipids are fats or fat-like substances (fatty acids, fatty oils, waxes, sterols, and esters of fatty acids) found in plants and animals. Lipids eaten with food are a source of energy and other body nutrients, or they are stored in fat (adipose) tissue. The plasma lipids consist of combinations of cholesterol and triglycerides carried on lipoprotein molecules through the blood stream. Excess levels in the blood (hyperlipemia) is closely associated with the development of coronary heart disease.
Cholesterol --- Cholesterol is a white crystalline or waxy substance found in egg yolk, all animal fats, bile, gallstones, nervous tissue, and blood. Almost all body tissues contain cholesterol but it is concentrated in the liver, blood, and brain. Cholesterol is only created in animals, not plants. The body makes all the cholesterol it needs, primarily in the liver, as an essential nutrient for repairing cell membranes, making vitamin D on the skin's surface, and creating hormones such as estrogen and testosterone. Cholesterol can't dissolve in blood, so it has to be carried by lipoproteins. An excess level of cholesterol in the blood (hypercholesterolemia) is a major risk factor for heart disease
Triglycerides --- Triglycerides are lipids and the chief constituent of fat in foods, blood and fat reserves in the body. They provide energy to the body. Calories eaten in a meal and not used immediately are converted to triglycerides and transported to fat cells to be stored. Hormones regulate the release of triglycerides from fat tissue to meet energy needs between meals. Triglycerides are carried along with cholesterol on the lipoproteins, which serve as transport in the bloodstream.
Medical researchers believe elevated triglyceride levels (hypertriglyceridemia) contribute to heart disease. High triglyceride levels displace HDL cholesterol (the good cholesterol) and the body converts triglyceride carriers into Very Low Density Lipoprotein (VLDL cholesterol) ---which is more dangerous than LDL. High triglyceride levels seem to reflect a lower activity level of enzymes which break down fats in the blood. Triglycerides may also be responsible for the development of blood clots in the arteries. High triglycerides are often associated with insulin resistance, obesity (particularly around the abdomen), and diabetes. (See PCBs and Diabetes)
Researchers in Boston studied 350 heart attack patients and found that those with high triglyceride levels had an almost three-fold risk of heart attack compared to patients with low levels. Furthermore, patients with the highest triglyceride/HDL ratio had a risk 16 times greater than patients with the lowest ratios. Patients with high triglyceride levels were more likely to be males, diabetic, hypertensive, have a higher body mass index, have a higher level of physical activity, and drink more alcohol. (From: "Fasting Triglycerides, High-Density Lipoprotein, and Risk of Myocardial Infarction", Circulation, 96(8): 2520-2525; Amer. Heart Assoc. Oct. 21, 1997.)
Low Density Lipoproteins (LDL) --- This lipid is the major cholesterol carrier in the blood, carrying about 75% of the body’s circulating cholesterol, and is often referred to as the "bad" cholesterol. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries, contributing to atherosclerosis. LDL can penetrate artery walls to interact dangerously through a process called oxidation caused by unstable molecules called oxygen-free radicals. These particles are released naturally during the body's chemical processes and increase when the body is exposed to environmental toxins, such as cigarette smoke. Free radicals help fight bacteria, but in excess cause harm. Free radicals tend to bind with any other molecule in the body and become destructive. If LDL collects on artery walls, free radicals released from the wall membranes attack and modify its form. The resulting oxidized form of LDL triggers white blood cells in the immune system to gather at the site, forming the plaques of atherosclerosis. Oxidized LDL may also impair nitric oxide, a chemical that helps relax the blood vessels and allow blood to flow freely.
High Density Lipoproteins (HDL) --- This is the "good" cholesterol. HDL removes excess cholesterol and LDL from the blood and walls of the arteries and returns it to the liver, where it can be passed out of the body. High HDL levels (above 45 mg/dl) appear to protect arteries from dangerous narrowing and so help prevent heart attacks. In one study, HDL levels below 35 mg/dl were strongly predictive of death from coronary artery disease.
Lipoprotein(a) --- Studies are finding an elevated risk for angina and first heart attacks in people with elevated levels of a cholesterol-carrying molecule called lipoprotein(a), or lp(a). The molecules have a structure similar to LDL and carry a protein that may deter the body's ability to dissolve blood clots and so may contribute to heart attacks. On the other hand, high levels of lp(a) may merely be by-products of long-term injury to the arteries that serve only as markers of late-stage atherosclerosis.
Albumin --- Serum albumin is the highest concentration protein in plasma. It transports many molecules in the blood (such as bilirubin, fatty acids, calcium, progesterone, cortisol, drugs and thyroxine). Albumin is responsible for much of the colloidal osmotic pressure of the blood, and is an important factor in regulating the exchange of water between the plasma and the interstitial compartment (keeping fluid from leaking out into the tissues).
Recommended Lipid Levels for People Without Heart Disease
The following are generally recommended blood plasma lipid levels for people without heart disease. Cholesterol levels must be interpreted after accounting for other risk factors, such as smoking, obesity, diabetes, etc.
Type Desirable Level (mg/dL) Undesirable Level (mg/dL)
Total Cholesterol
Below 200
Above 240
LDL Cholesterol
Below 130
Above 160
HDL Cholesterol
Above 45
Below 35
Triglycerides
Below 200
Above 400
The Social and Economic Costs of Heart Disease
Heart disease is the leading cause of death in the U.S., accounting for nearly 740,000 deaths each year (287 deaths per 100,000 population), and cerebrovascular disease (stroke), the third leading cause of death, accounts for about 150,000 deaths each year (58/100,000) In 1995, the American Heart Association estimated that approximately 1.5 million Americans would suffer a myocardial infarction, and one third would not survive the event. Although mortality from heart disease has declined steadily over the past three decades in the U.S., the total burden of coronary disease is predicted to increase substantially over the next 30 years due to the increasing size of the elderly population. The cost of medical care and lost economic productivity due to heart disease in the U.S. was projected to exceed $60 billion in 1995.
The studies listed in this report show that PCBs could be a factor in some of these serious health problems, especially in areas such as Northeast Wisconsin with a long history of elevated PCB levels in the fish, water and air, and numerous occupational PCB exposures.
Go to Summaries of 60 Studies linking PCBs and Heart Disease
The information listed above, except for the PCB discussion, was condensed from the following websites:
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