Life Extension Magazine®

Issue: Oct 2005

Why Our Arteries Become Clogged As We Age


By John Colman.

Artwork of a human heart showing narrowing of the coronary arteries due to atherosclerosis on the artery wall. The narrowing causes abnormal clotting, which blocks the vessel and starves the heart muscle of blood, causing a heart attack.


Despite aggressive intervention with diet, exercise, supplements, and drugs, pathological changes still occur in the arterial wall that predispose aging adults to vascular diseases. The encouraging news is that a non-prescription method has been developed to address the underlying reason why arteries become occluded as people reach the later stages of their lives.

For the past 35 years, the standard way to treat coronary atherosclerosis has been to bypass the blocked arteries. Recuperation from coronary bypass surgery can take months, and some patients are afflicted with lifetime impairments such as memory loss, chronic inflammation, and depression.1,2

The scientific literature reveals that atherosclerosis is associated with high blood levels of homocysteine, C-reactive protein, insulin, iron, low-density lipoprotein (LDL), and triglycerides, along with low levels of high-density lipoprotein (HDL) and testosterone. Optimizing blood levels of these substances can dramatically reduce heart attack and stroke risk.3-14

Prescribing a “statin” drug is what today’s doctors typically do to prevent and treat coronary atherosclerosis. Cholesterol and LDL, however, are only partial players in the atherosclerosis process.

Mainstream cardiologists fail to appreciate that coronary atherosclerosis is a sign of systemic arterial dysfunction requiring aggressive therapy to correct. Health-conscious adults have grown impatient with doctors who do not translate research findings into improved therapies. More than ever before, people are taking responsibility for the health of their arteries by correcting as many of the known risk factors as possible.

A coronary artery with atherosclerosis. [enlarge image]

Anatomy of the Artery

Arteries are the blood vessels that bear the full force of each heartbeat. Laypeople often think of arteries as flexible tubes whose only function is to carry blood that flows continuously throughout the body. In reality, arteries are dynamic, functioning muscular structures that in good health expand and contract to facilitate circulation and maintain optimal blood pressure.

The artery’s outer layer mostly consists of connective tissue and provides structural containment for the two layers beneath. The middle arterial area comprises elastic smooth muscle that provides the contractile strength to make possible the artery’s expansion and contraction with each heartbeat. The inner layer—known as the endothelium—consists of a thin area of endothelial cells whose integrity is crucial if atherosclerosis is to be prevented.

A vital function of the endothelium is to form a barrier to prevent toxic substances in the blood from entering the elastic smooth muscle in the middle vessel wall. Another specialized function of the endothelium is to react to mechanical forces such as blood pressure and blood flow generated by the heart’s beating action. The endothelium releases substances into cells of the middle layer smooth muscle that changes the tone or firmness of the artery.

When endothelial cells sense an injury, they produce signals that prompt smooth muscle cells in the middle arterial wall to change. These changes result in the smooth muscle cells moving toward the site of vascular injury, where they reposition themselves just beneath the endothelial cell layer. In reaction to injury, endothelial cells also produce substances that signal circulating blood cells to stick to the endothelium (instead of effortlessly flowing through the vessel). Atherosclerosis gradually forms in response to this initial injury to the endothelium.

Cross-section of a narrowed coronary artery partially blocked by atherosclerotic plaque. [enlarge image]

Changes in the Aging Endothelium

As we grow older, some of the specialized functions of our endothelial cells become blunted. The self-renewal process weakens. The endothelial barrier becomes leaky. Signals to the middle wall smooth muscle cells that regulate their function become altered.

Smooth muscle cells behave as if in reaction to endothelial injury, migrating to the endothelium, where they multiply and produce matrix proteins that gradually occlude the blood vessel. The addition of these smooth muscle cells and matrix proteins within the sub-endothelial space results in thickening of the artery’s inner wall. In older arteries, the inner wall becomes a battleground where multiple reactions occur that are similar to the process of chronic injury. The inner wall dysfunction that occurs in the aging artery provides fertile soil for the seeds of atherosclerosis. All of these processes whereby normal endothelial function is compromised are collectively referred to as endothelial dysfunction.

How Atherosclerosis Develops

Atherosclerosis is so common in older adults that some experts used to think it was part of normal aging. An alternative view is that atherosclerosis is a disease process that takes advantage of changes that occur within the aging artery.

The vascular aging process and atherosclerotic process influence each other and become intertwined as we age. The more severe vascular aging is, the easier it is for atherosclerosis to take hold. The more severe atherosclerosis is, the greater its impact on diseases associated with vascular aging, such as stroke and heart attack. Thus, it appears that with advancing age, atherosclerosis and the aging process combine forces.

An often-used analogy for atherosclerosis is a “clogged pipe.” This misguided perception either leads to bypass surgery or a procedure in which the blocked coronary artery is forced opened with a balloon catheter (angioplasty) and a stent is implanted to keep the artery open. While these surgical procedures have become necessary for many people, the “clogged pipe” analogy is an inaccurate way to view the process of atherosclerosis.

Atherosclerosis begins with changes in endothelial cell function that cause white blood cells moving through the blood to stick to the endothelium instead of flowing by normally. The endothelium becomes weakened, which allows blood cells and toxic substances circulating in the blood to pass through the endothelium and enter the artery’s sub-endothelial compartment. Lipid or fat cell-like substances in the blood, such as LDL and triglycerides, then accumulate in this area.

Cross-section through an artery obstructed with atheroma plaque. The muscular wall of the artery (orange) takes up much of the image. At center, fatty deposits of plaque (gray) are seen on the inner arterial wall; the lumen (black) has been severely reduced for the flow of blood. Narrowing of the artery disrupts blood flow and may result in clot formation or severe artery blockage that can prompt a heart attack. [enlarge image]

The lipids that accumulate in the broken endothelium become oxidized. This causes them to signal the endothelial cells, which then alert smooth muscle cells to begin a “repair” process that eventually results in an atherosclerotic lesion. Depending on a person’s individual risk factors (such as poor diet, lack of exercise, smoking, high blood pressure, and the aging process itself), fat accumulation continues and the atherosclerotic process accelerates.

White blood cells called macrophages then invade the area to digest the fat. Smooth muscle cells that have migrated to the area have already changed their nature to also scavenge fat. These fat-laden white blood cells and smooth muscle cells, which are called “foam cells,” induce chronic inflammatory attack by various immune components. Smooth muscle cells try to curtail the injury to the endothelium by producing collagen, which forms a cap over the injury site. Then calcium accumulates and forms a material resembling bone. This is why atherosclerosis used to be referred to as “hardening of the arteries.”

This complex array of foam cells, calcification, and lipid accumulation is called an atherosclerotic plaque. The plaque grows, and if it becomes unstable, is vulnerable to acute rupture that exposes its contents to the blood. Platelets can then rapidly accumulate around this ruptured plaque, resulting in a blockage (or blood clot) on the inner surface of the blood vessel wall. This clot can become very large and occlude the vessel. Even small plaques, if they rupture, can interfere with blood flow and cause an acute heart attack.

Alternatively, atherosclerotic plaques can enlarge to such a degree as to completely block blood flow. When blood flow within an artery is severely compromised by a large plaque or blood clot, the cells of tissues that depend on blood flow from that artery become damaged or die. Coronary atherosclerosis cuts off the heart’s blood supply by occluding the heart’s arteries, thus stopping the oxygen supply to the heart and causing a heart attack. A stroke results when atherosclerosis processes cut off the oxygen supply to a portion of the brain.


The Arterial Wall Under Attack

High blood pressure, elevated LDL and triglycerides, low HDL, cigarette smoking, diabetes, obesity, and lack of exercise contribute to endothelial dysfunction and the subsequent development of atherosclerosis.15-25

Additional endothelial-damaging factors include excess levels of glucose, insulin, iron, homocysteine, fibrinogen, and C-reactive protein, as well as low HDL and free testosterone (in men).3,9,10,24,26-28

Homocysteine is particularly dangerous because it can induce the initial injury to the endothelium. Homocysteine then facilitates oxidation of the fat/LDL that accumulates beneath the damaged endothelium, and finally contributes to the abnormal accumulation of blood components around the atherosclerotic lesion.29

Fibrinogen is a clotting factor that accumulates at the site of the endothelial lesion. Fibrinogen may contribute to plaque buildup or participate in blood clot-induced blockage of an artery after an unstable atherosclerotic plaque ruptures.30



C-reactive protein is not only an inflammatory marker, but also directly damages the endothelium. Chronic inflammation, as evidenced by persistent high levels of C-reactive protein, creates initial injuries to the endothelium and also accelerates the progression of existing atherosclerotic lesions.3,27

In response to numerous published studies, health-conscious people are altering their diets, taking drugs, hormones, and dietary supplements, and trying to exercise regularly in order to reduce these atherosclerosis risk factors. However, these efforts alone cannot be completely successful because age itself is a major risk factor for atherosclerosis.

Atherosclerotic risk conferred by age is attributable in large measure to pathological endothelial dysfunction.37,38 As noted earlier, endothelial dysfunction is not synonymous with atherosclerosis, but the two processes are increasingly intertwined with advancing age.


Maintaining the endothelium’s integrity is crucial to protecting against occlusive atherosclerosis and helping to keep blood pressure under control. The four primary functions of endothelial cells are to:

  • Form a barrier to prevent toxic substances from entering the smooth muscle in the middle arterial wall;
  • Sense mechanical forces (pressure and/or flow) and release substances that act to change the “contractile tone” of the smooth muscle medial layer;
  • Release substances into the blood to change the function of blood platelets, making them more or less sticky;
  • Sense arterial wall injury and produce substances to change the nature of smooth muscle cells in the middle layer of the artery. This causes smooth muscle cells to migrate to the area of endothelial injury, and signals blood cells to stick to endothelial cells.

Poor health habits and normal aging result in endothelial dysfunction, a pathological process that is initiated when the endothelial boundary lining the arteries is broken. Atherosclerotic lesions form in response to endothelial injury.

Cross-section of an artery demonstrating plaque. [enlarge image]

Maintaining Vascular Health During Aging

Endothelial cells line the arteries, veins, arterioles, and capillaries of the vascular system. Twenty years ago, the endothelium was seen as a relatively inert structure that played no active role in vascular function. Since then, however, research has shown that the endothelium is dynamic and participates in vital aspects of arterial structure and function.39

Arterial blood vessel dilation depends on endothelial cells triggering the production of a signaling molecule called cyclic guanosine monophosphate (cyclic GMP) in the muscle cells. Cyclic GMP prompts a change in calcium flux at the smooth muscle cell surface, producing relaxation of the muscle. Relaxation of the artery muscle cells allows the artery to expand and then subsequently contract, helping to pump blood back to the heart.40 Nitric oxide production by endothelial cells also regulates vascular tone, changes cardiac contraction, prevents vessel injury, and helps prevent the development of atherosclerosis. Once atherosclerosis is present, however, endothelial cells cannot function properly, and this blocks nitric oxide-induced dilation, thus stiffening the arteries.

The endothelium’s ability to manufacture enough nitric oxide to maintain artery dilation is one of its most crucial functions. When arteries lose their ability to respond to sudden increased demand for blood flow, endothelial dysfunction develops. This condition is a hallmark of cardiovascular disease.

Endothelial dysfunction is also the earliest measurable functional abnormality of the vessel wall. Tests of endothelial dysfunction may detect abnormalities in the initial stages of atherosclerotic disease before clinical symptoms are present.40,41 In subjects with coronary artery disease, hypertension, and hypercholesteremia, endothelial dysfunction is always present.41 Furthermore, endothelial dysfunction is present in type I and type II diabetes, and is related to the development of diabetic vascular complications.41

Preventing endothelial dysfunction may be possible through innovative nutritional strategies. Emerging research suggests that propionyl-L-carnitine and PEAK ATP™ may protect cardiovascular health by preventing endothelial dysfunction, restoring healthy endothelial function, and optimizing the energy available to cardiac and vascular cells. PEAK ATP™ also works synergistically with propionyl-L-carnitine to protect cardiovascular function while promoting enhanced cellular energy for people with conditions ranging from chronic fatigue syndrome to erectile dysfunction.42,43

Propionyl-L-Carnitine (PLC)

Research suggests that propionyl-L-carnitine (PLC) plays an important role in protecting the function and health of endothelial cells.44-46 Studies also indicate that PLC may act as a nutritional corrective agent, relieving clinical symptoms of cardiovascular conditions such as peripheral arterial disease, angina, coronary artery disease, cardiomyopathy, intermittent claudication, ischemic heart disease, atherosclerosis, and congestive heart failure.47-54 PLC appears to be more potent than L-carnitine in improving vascular function.55

PLC passes across the mitochondrial membrane to supply L-carnitine directly to the mitochondria, the energy-producing organelles of all cells. Carnitines are essential for mitochondrial fatty acid transport and energy production. This is important because heart muscle cells and endothelial cells burn fatty acids rather than glucose for 70% of their energy. By contrast, most cells generate 70% of their energy from glucose and only 30% from fatty acids.56

Carnitine deficiency has been associated with congestive heart failure.50 PLC supplementation has been reported to increase exercise capacity, optimize energy production, and reduce ventricular size in patients with congestive heart failure.50







PLC Improves Physical Performance

Intermittent claudication is a condition caused by narrowing of the leg arteries. Patients typically experience pain in their calf muscles that makes walking long distances difficult or impossible.

In a 24-week study, patients supplemented with PLC gradually increased the distance they were able to walk on a treadmill by up to 73%. The study authors concluded, “The response rate during the entire titration course was significantly in favor of [PLC] compared with placebo. Although the precise mode of therapeutic action requires clarification, [PLC], at a dose of 1000 mg to 2000 mg a day appears to be effective and well tolerated, with minimal adverse effects.”60

Several studies have shown that PLC increases the walking capacity of patients with peripheral arterial disease. A study comparing PLC to L-carnitine showed that PLC increased patient walking distance from 245 to 349 meters, while carnitine was only slightly better than placebo.55 Ultrasound testing found that PLC acts through a metabolic mechanism rather than by altering blood velocity or flow.55 Another study suggested that PLC increases muscle strength in patients with peripheral arterial disease.54

PLC and Male Sexual Dysfunction

In a study of male sexual dysfunction, testosterone supplementation was compared to supplementation with a combination of oral PLC and acetyl-L-carnitine. Both the carnitine combination and testosterone improved the following penile functions: peak systolic velocity, end-diastolic velocity, resistive index, nocturnal penile tumescence, and the International Index of Erectile Function score.

The combination of 2 grams each of PLC and acetyl-L-carnitine daily was more effective than testosterone at improving nocturnal penile tumescence and the International Index of Erectile Function score, an important measure of erectile and sexual function. PLC and acetyl-L-carnitine thus appear to be safe, effective agents for managing male sexual dysfunction.42

PLC and Chronic Fatigue

In a landmark study, researchers examined carnitine’s effects on patients with chronic fatigue syndrome. In this 24-week study, investigators followed three groups of 30 patients who supplemented daily with 2 grams of acetyl-L-carnitine, 2 grams of PLC, or a combination of the two.

The results were remarkable: the clinical global impression of change after treatment improved significantly in 59% of the patients taking acetyl-L-carnitine and in 63% of patients taking PLC. While the main effect of acetyl-L-carnitine was improving mental fatigue, PLC helped to improve symptoms of general fatigue.43

Replenishing Cellular Energy Stores

Adenosine triphosphate (ATP) is the primary molecule used by all human cells as energy currency. ATP is stored in the organs and red blood cells, but is especially concentrated in the liver. A study measuring ATP levels in human red blood cells found that people in their seventies had about 50% less ATP than young adults in their twenties.61

For 40 years, scientists have worked to create an effective, orally ingested form of ATP that is able to boost endogenous ATP levels. Five years ago, they developed an orally administered ATP that can effectively raise pools of ATP throughout the body.62-64 Orally administered ATP expands ATP in the liver, red blood cells, blood plasma, and organs. Supplemental ATP improves blood vessel tone and relaxes blood vessel walls, increasing blood flow to the lungs, heart, and peripheral areas without affecting heart rate or blood pressure.62-64

ATP supplementation can also elevate the body’s intracellular and extracellular stores of ATP, providing increased energy and improved athletic performance. Additionally, ATP supplementation enhances the delivery of glucose, nutrients, and oxygen to recovering and working muscles, while speeding the muscles’ removal of waste products. ATP benefits muscle growth, recovery, and strength, and lessens the perception of fatigue and exercise-associated pain.62 Supplementing with ATP helps to restore youthful levels of ATP in the body.62,63,65,66

Studies Confirm Benefits of PEAK ATP™

The patented brand of ATP tested in numerous human and animal studies—PEAK ATP™—elevates red blood cell and plasma ATP levels, producing effects similar to those achieved by intravenous ATP administration.62-64 Studies show that PEAK ATP™ is readily absorbed, broken down into adenosine and organic phosphate, and incorporated in the liver and red blood cells to raise ATP pools. PEAK ATP™ boosts circulating ATP levels for at least six hours and should reach a steady-state plasma level within 24 hours.62-64

When administered orally to rabbits, ATP regulates and normalizes their cardiopulmonary functions, increasing blood flow, reducing overall vascular resistance, and increasing arterial oxygen pressure.65 In baboons, ATP infusions increased cerebral blood flow by nearly 50% and boosted oxygen consumption in the brain.65

Red blood cells.

During exercise, vascular blood flow increases due to the release of ATP into the blood. Infusing ATP into the legs of resting subjects increases blood flow in the thighs similar to that produced by exercise, suggesting that exogenously administered ATP may likewise promote increased circulation.66

Recent studies show that arterial and vein diameter is regulated by red blood cells sensing low blood oxygen levels. The red blood cells then release ATP, which produces endothelial vasodilation, or widening of the arteries. This mechanism of artery widening has been demonstrated in studies involving various species and tissues.67,68 Thus, red blood cells use ATP to help meet local tissue oxygen needs. Ensuring adequate red blood cell pools of ATP to help regulate vascular tone is now seen as critical to maintaining circulatory health.68

ATP release decreases with advancing age, which may be a cause of age-related increases in blood pressure. In fact, patients with primary pulmonary hypertension have been shown to suffer from impaired ATP release from red blood cells.69 This is also true of patients with cystic fibrosis who also develop pulmonary hypertension.70

Adenosine, a breakdown product of ATP, may act as an endogenous protector of the heart. Research suggests that through various chemical processes, adenosine may inhibit the damaging effects of ischemic heart disease and heart failure.71 Adenosine may increase coronary blood flow and alleviate the harmful effects of chronic heart failure.71

Adenosine is released from the heart primarily when the heart’s oxygen supply is limited as a result of increased oxygen consumption during exercise, restricted blood flow due to atherosclerosis, or ischemic events such as heart attack.71 Thus it is vitally important to maintain optimal levels of adenosine produced by the heart and arteries internally, as well as of adenosine supplied from external sources such as dietary plant and animal foods


Atherosclerosis remains the number-one cause of death and disability in the United States. The endothelial cells that line blood vessels are crucial to maintaining vascular integrity. Endothelial dysfunction is a critical factor in the initiation and progression of cardiovascular disease.


Together, these two powerful compounds support optimal cellular energy and vascular health.


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