Cardiovascular Disease: The American Epidemic
Cardiovascular Disease Demographics
Heart attack, coronary heart disease, congestive heart failure, congenital heart disease, and stroke: the mere mention of these terms is sure to elicit some concern, if not understanding, in the average American. The prevalence of cardiovascular disease (CVD) in the United States makes it something akin to an epidemic. Afflicting 81.1 million people and claiming the lives of 831,300 people in 2006 alone, CVD has become America's leading cause of death. In fact, the American Heart Association estimates that 34.3% of all deaths in 2006 were caused by CVD. The number of deaths due to CVD far outstrips deaths caused by cancer, and AIDS (American Heart Association). The prevalence of heart disease comes at a high economic cost. In 2010, Americans spent a staggering amount of $503.2 billion dollars on healthcare expenses to treat and prevent cardiovascular diseases (Lloyd-Jones et al).
History of Cardiovascular Disease
Heart disease is commonly dubbed 'the modern' epidemic. Before the 19th century, heart disease was much less prevalent due to the structure of society and the overall lifestyle of the average person. During these times, agricultural societies were more common, with most people performing manual labor to earn a living. Every task had to be done by hand because of the lack of machines; tasks such as washing clothes and even cooking required more effort. Laundry had to be washed and wrung by hand. Procuring water for cooking was an arduous task and involved walking over long distances carrying heavy containers. Walking was the most affordable form of transportation and, coupled with manual labor, kept the population physically fit (The Franklin Institute). Furthermore, the diet of the average person was healthier than it is today, consisting of naturally grown, unprocessed foods. The daily diet was rich in protein and contained less carbohydrates, fats, and salt. Only wealthy upper classes could afford expensive, unhealthy foods. Therefore most people had less adipose tissue and better blood circulation, making them less likely to suffer from cardiovascular diseases (The Franklin Institute, Ruddy).
Industrialization in the 19th century created less physically demanding and more sedentary lifestyles. With the advent of machines, people did not have to perform all tasks manually. Vehicles were developed for transportation and machines were created to produce mass quantities of processed food, thereby making everyday life easier. As machines became more common, people started eating unhealthy processed foods rich in carbohydrates, fats, and salt. Household tasks did not require as much physical activity as in the past. Industrialization created the first spark of a reliance on machines, and the development of technology continued to progress. Today, technology that meets our every need with a minimal amount of individual effort is prevalent. This has led to unhealthy lifestyles and diets, contributing to a greater incidence of cardiovascular disease. Thus, as the standard of living has improved, it has also worsened general health as incidences of cardiovascular disease have risen (The Franklin Institute, Ruddy).
The major risk factors for heart disease fall into two categories: unmodifiable and modifiable. Unmodifiable risk factors include old age, family history of heart disease, and male gender. Modifiable risk factors are those affected by lifestyle choices. These include high blood cholesterol (also known as hyperlipidemia), lack of exercise, diets high in saturated fats, use of tobacco smoke, alcohol abuse, high blood pressure, obesity, and diabetes mellitus (Cleveland Clinic, World Health Federation).
While these factors may be linked to genetics, they also are associated with the modern lifestyle. For example, diets high in cholesterol, saturated fats, and carbohydrates lead to plaque formation within arteries, causing atherosclerosis. Alcohol abuse increases triglyceride levels within the blood, damages heart muscle, and contributes to high blood pressure, one of the risk factors of heart disease (Johns Hopkins Medicine, "High Cholesterol And Triglyceride Levels"; World Health Federation). Stress also acts as a compounding factor, causing people to overeat, drink, and smoke (Ingham Regional Medical Center).
Contribution of Excess Cholesterol to Atherosclerosis
Even though high cholesterol consumption can cause heart disease, the human body does depend on cholesterol for the formation of cell membranes, hormones, and other tissues. Cholesterol is a lipid synthesized by the liver and consumed through foods as dietary cholesterol, including high cholesterol foods such as meat, poultry, seafood and dairy products. All cholesterol travels through the blood in two forms: low density lipoprotein (LDL) and high density lipoprotein (HDL). Both LDL and HDL are composed of proteins and cholesterol; while LDL is high in cholesterol and low in protein, HDL is low in cholesterol and high in protein.
The function of LDL is to deliver cholesterol to organs to be used in cell membrane formation and hormone synthesis. However, if excess cholesterol is present, LDL will deposit this cholesterol in the arterial walls as plaque, making the arterial walls narrow and lowering blood flow. This narrowing of the arteries, shown in Figure 1, is known as atherosclerosis. HDL, on the other hand, reduces the amount of cholesterol in the blood by delivering excess cholesterol in the blood to the liver to be broken down. Therefore, LDL is known as "bad" cholesterol while HDL is known as "good" cholesterol (MedicineNet).
Most Common Types of Heart Disease
The most common type of heart disease in adults is coronary artery disease (CAD), which is caused by atherosclerosis in the coronary arteries, which is shown in Figure 2. CAD can cause angina, or chest pain when the heart does not receive enough oxygenated blood; or a heart attack (also known as a myocardial infarction) when total blockage of the coronary artery completely prevents oxygenated blood from being delivered to the cardiac muscle (National Heart Lung and Blood Institute).
National Heart Lung and Blood Institute
When atherosclerosis takes place in an artery that provides blood to the brain, this can cause an ischemic or hemorrhagic stroke. There are two types of ischemic strokes: thrombotic and embolic. A thrombotic stroke occurs when an artery in the brain is completely blocked, preventing oxygenated blood from reaching a certain region in the brain. An embolic stroke takes place when a clot in an artery breaks off and travels to an artery in the brain, causing blockage of blood flow through that artery. Ischemic strokes also can take place from narrowing of an artery in the brain even if the vessel is not completely blocked. Hemorrhagic strokes take place when plaque buildup in an artery in the brain causes the blood vessel to weaken and rupture, causing the blood to leak into the brain and cause damage to brain cells (Rodriguez).
CAD or past heart attacks may contribute to more cardiovascular problems in the future, including cardiomyopathy, cardiac arrhythmias, or congestive heart failure. Cardiomyopathy involves the thickening of the cardiac muscle, which weakens the heart and makes it more difficult for it to deliver blood to body tissue in systemic circulation. (Mayo Clinic Staff). Cardiac arrhythmia is an irregular heartbeat, which may be caused by dysfunction of the heart's atria, ventricles, or nodes (Johns Hopkins Medicine, "Cardiac arrhythmias"). Congestive heart failure takes place when narrowed arteries from CAD or scar tissue from a past heart attack prevents blood from flowing properly from the heart to body tissues, resulting in an imbalance of blood flow into and out of the heart. As blood flow out of the heart slows down, the blood begins to build up in the veins and cause edema, or swelling, of legs, ankles, or other parts of the body (O'Brien).
Recent Findings: Cardiovascular Disease Risk Factors
Since patients may often have a poor prognosis after cardiovascular events, those at high risk for heart disease should take extra precautions and maintain a healthy lifestyle to prevent onset of cardiovascular problems. Studies are being done to identify risk factors for heart disease and to study their role in diminishing cardiovascular health. Researchers at the University of Missouri-Kansas City School of Medicine sought to determine the effects of obesity and atherosclerosis-promoting risk factors on the cardiovascular health of children. They recruited a group of 70 children from the ages of 9 to 16 with risk factors for obesity and atherosclerosis including hypertension, insulin resistance, tobacco smoke exposure, and familial dyslipidemia. Carotid artery ultrasounds were performed in these children to measure the thickness of their carotid arteries. The findings, which were published in the American Heart Association's journal Circulation in 2009, showed that children with high blood triglycerides and obesity had higher arterial thickness and BMI, increasing their risk for heart disease. These results emphasize the role of excess cholesterol levels in undermining cardiovascular health (Le et al).
While it is true that modern lifestyle contributes to heart disease, there may be other factors that are also involved. Recent studies suggest that the iconic risk factors associated with heart disease – lack of exercise, high consumption of cholesterol, and habits such as frequent smoking and alcohol abuse – might not be the only ones to blame for the problem.
A meta-analyses conducted by Dr. Tuula Paajanen and colleagues and published in the European Heart Journal suggested that height might play a role in causing cardiovascular disease. The systematic review, conducted at the University of Tampere in Finland, aimed to elucidate the relationship between height and heart risk, which has been the subject of many studies dating as far back as 1951. Paajanen and her colleagues studied data from 52 of these studies, resulting in a comprehensive analysis of over 3 million people. They found that men under 5'5 and women under 5'0 are 50% more likely to develop heart problems than are their taller counterparts. The findings from this review suggested that height could be a major risk factor for cardiovascular disease (Paajanen et al).
Despite the implications of this study, height is not a set determinant of cardiovascular risk. Dr. Michael Lauer, the director of the division of cardiovascular sciences at the National Heart, Lung, and Blood Institute, asserts that short stature does not necessarily indicate higher risk. Height is determined by many factors that include, but are not limited to, nutrition, exposure to pollution, and genetics. Children who are improperly nourished in the womb and after birth have impaired growth compared to other children. As they get older, these children gain weight more rapidly and accumulate excess fat that makes then them more susceptible to heart problems. Therefore, short height may be caused by heart disease risk factors and is likely not a risk factor itself. Nevertheless, Drs. Lauer and Paajanen agree that while patients cannot modify their height and other potential heart disease risk factors controlled by genetics, people with more risk factors should take extra precautions to improve their health and prevent cardiovascular disease (Klein).
Cardiovascular Disease Prevention
Measures such as maintaining a healthy diet and exercising regularly can prevent or control cardiovascular disease risk factors. A study conducted at the University of Pittsburgh School of Medicine examined the effects of diet and exercise interventions in severely obese adults and found that a healthy diet combined with physical activity resulted in significant weight loss. These interventions were conducted over the span of one year, and resulted in a decrease in visceral abdominal fat, hepatic fat, and blood pressure, showing that a healthy lifestyle can reduce risk factors for cardiovascular disease (Goodpaster et al).
According to the Departments of Agriculture and Health and Human Services, no more than 5.8 grams of salt should be consumed by a single person each day. However, the amount of salt in the average American's diet far exceeds that amount. A study conducted at the Department of Medicine at the University of California, San Francisco on the effect of salt intake showed that decreasing the amount of salt consumed by 3 grams per day would decrease the number of new cases of coronary heart disease by 60,000 to 120,000 and stroke by 32,000 to 66,000. About 75% to 80% of the salt in an average American's diet comes from processed foods, which are also high in carbohydrates and fats. According to this study, avoiding such high sodium, unhealthy foods would significantly decrease risk of a cardiovascular event (Bibbins-Domingo).
Developing New Treatments and Prevention Measures
A study conducted by researchers at UT Southwestern Medical Center found a potential mechanism of recovering damaged cardiac tissue. The study, which was published in February 2011 in Science, assessed the effect of removing cardiac tissue from the hearts of newborn mice. When about 15% of cardiac tissue was removed, the heart was able to regenerate the lost tissue within three weeks, resulting in a normal, whole, and functioning heart. This indicates that the newborn mammalian heart can repair itself, an ability that is lost as the organism matures into an adult. The authors of this study believe that uninjured beating cells called cardiomyocytes stop beating in order to duplicate themselves and replace the lost tissue. Cardiomyocytes possess this regenerative ability only for a specific period of time after birth and cannot be found in the adult mammalian heart (Porrello et al).
When cardiac tissue in an adult heart is damaged or lost, such as after a heart attack, the tissue's inability to regenerate itself renders the heart weaker. This leads to susceptibility to heart failure resulting in death. Therefore, an understanding of the regenerative properties of cardiomyocytes could lead to treatments that make use of this regenerative ability and allow repair after heart damage from a cardiovascular event. Further research in this area will play an important role in the future of heart disease.
While cardiovascular disease is a leading cause of death in the United States, studies are attempting to elucidate unknown risk factors and potential mechanisms of reducing associated risk factors. Improving lifestyle choices by exercising regularly, eating low cholesterol diets, and decreasing sodium consumption have been shown to reduce heart disease risk. As studies continue, physicians and researchers hope to develop better preventive measures and treatments for heart disease, leading to improved health and a better quality of life for those with cardiovascular disease.