21.10: Cardiovascular disease is a leading cause of death in the United States.

The heart is among the most neglected organs. Most people take it for granted. But diseases of the heart, including heart attacks, result in more deaths in the United States every year than any other single cause. They also are among the most avoidable of all causes of death. In 2009, just over 24% of the deaths in the United States were caused by diseases of the heart. Heart attacks are brought on by an interruption in the flow of blood through one of the coronary arteries—the blood vessels that deliver oxygen and nutrients to the heart muscle itself. When cells in the heart muscle are deprived of oxygen, the heart may beat irregularly or cease to beat, and the heart muscle cells deprived of oxygen die. This has serious and long-term implications, because heart cells are among the cells of the body with the lowest rates of cell division and renewal—usually less than 1% per year. Heart attacks rarely strike out of the blue. Although the heart attack itself is a sudden event, it usually occurs after decades of progressive deterioration of the arteries and other degradations of the circulatory system, collectively called cardiovascular disease (FIGURE 21-20).

Figure 21.20: Diseases of the heart and blood vessels. Fatty deposits and damage to arteries can disrupt blood flow and interfere with proper circulation.

“Broken heart. A pump after all, pumping thousands of gallons of blood every day. One fine day it gets bunged up and there you are.”

JAMES JOYCE, Ulysses

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Cardiovascular disease includes all diseases of the heart and blood vessels and is ultimately responsible for close to half of all deaths in the United States. In addition to heart attacks, strokes are a common outcome of advanced cardiovascular disease. Caused by blocked arteries or blood clots in the brain, strokes also lead to cell death in the brain tissues starved of oxygen. There is, however, some cause for optimism: the death rate from heart disease has been declining steadily for the past 50 years, including a 25% drop in the past 20 years. These reductions have come, not from advances in heart transplants and other surgical interventions, but rather from improvements in diet and exercise as well as advances in diagnosis and preventive medicine.

Cardiovascular disease generally begins with the development of fatty deposits called plaques on the inner walls of arteries. Plaques increase the risk of formation of blood clots and, by narrowing the artery, reduce the flow of blood. This narrowing of arteries, called atherosclerosis, is often followed by the depositing of calcium at the plaques, causing them to harden in a process known as arteriosclerosis. The initial formation of plaques is usually a consequence of circulating cholesterol in the bloodstream. Because most of this circulating cholesterol comes from cholesterol in our diet, we can reduce our risk of atherosclerosis by reducing our cholesterol intake.

All cholesterol is the same chemically, but you may hear references to “good” cholesterol and “bad” cholesterol. Why is this? As we discussed in Chapter 3, most cholesterol circulating in the bloodstream is packaged as LDL, or low-density lipoproteins. These molecules consist of thousands of molecules of cholesterol surrounded by a phospholipid coat. Because the LDL particles are sticky, they adhere to artery walls and can initiate the buildup of dangerous plaques. Other circulating particles, high-density lipoproteins (HDL), are considered “good” cholesterol. Less well understood than LDL, these particles seem to remove cholesterol from arteries and deliver it to liver cells, where it can be broken down. This process can actually reduce the progression of cardiovascular disease. By including in your diet fish and other foods that contain a specific type of fatty acids, called omega-3 fatty acids, you can increase your HDL levels.

Both nature and nurture play a role in cardiovascular disease. As we saw in Chapter 3, the tendency to develop cardiovascular disease is inherited. Individuals differ in the number of LDL receptors they produce on their liver cells, and the more receptors an individual has, the better that individual is able to remove atherosclerosis-causing cholesterol from circulation. You cannot alter the genes you inherit for LDL receptor production. But you can alter the amount of cholesterol or type of cholesterol (LDL vs. HDL) that is circulating in the first place. Several different behavioral changes, such as increasing aerobic exercise, not smoking, and eating a low-cholesterol, low-fat diet, can reduce the level of circulating cholesterol and the risk of cardiovascular disease (FIGURE 21-21).

Figure 21.21: Cholesterol can be helpful or harmful.

With aerobic training, such as running, the muscle fibers of the heart get bigger (in much the same way that skeletal muscle gets bigger when you lift weights), and cardiovascular health is improved. When people are sedentary, though, their hearts may have to work harder for reasons such as hypertension or poor diet. The increased load on the heart causes the heart to get bigger, but in a pathological manner that increases the risk of heart failure, rather than in a manner that increases strength and efficiency.

In summarizing its research-based recommendations for reducing risk factors for heart disease, heart attack, and stroke, the American Heart Association suggests a focus on “A, B, and C”:

Avoid tobacco

Be more active

Choose good nutrition

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These behavioral changes are much easier said than done, but because they include the most effective strategies for reducing the risk of cardiovascular disease, the payoffs are significant.

TAKE-HOME MESSAGE 21.10

Cardiovascular disease includes all diseases of the heart and blood vessels, including heart attacks and strokes, and is the leading cause of death in the United States. It generally begins with the development of fatty deposits on the inner walls of arteries that increase the risk of blood clots and reduce the flow of blood in coronary arteries that supply oxygen to the heart (atherosclerosis). Because the hardening of arteries (arteriosclerosis) is usually initiated by circulating cholesterol, it is possible to reduce the risk of cardiovascular disease by reducing cholesterol intake.

Compare the roles and importance of LDL, or low-density lipoproteins, and HDL, or high-density lipoproteins.