Heart Disease: Causes, Prevention, and Current Research

Heart disease is the leading cause of death in the United States. The causes and prevention of heart disease have been studied for years, and new information is emerging. For the last several decades, saturated fat and cholesterol have been thought to be major contributors to coronary artery disease, and therefore people are typically advised to strictly limit these in their diet. However, recent studies are indicating that it may not be wise to strictly limit the intake of dietary saturated fatty acids or replace them with polyunsaturated fatty acids when taking other health conditions into consideration. Depending on a person’s genetics, diet may or may not be an important factor in preventing heart disease. Exercise is also beneficial for everyone in preventing heart disease. When considering human development, including the negative effects of heart disease, humans still have a lot to learn about the human body and the interaction of diet, the environment, and genetics. Cover Page Footnote Pete Peterson, PhD, was the JCCC faculty adviser on this paper. This article is available in JCCC Honors Journal: http://scholarspace.jccc.edu/honors_journal/vol5/iss2/1 Human development can be defined as changes in the interactions between an individual and their environment across the lifespan. Development begins when a zygote is formed in utero and continues throughout the remainder of an individual‟s life. There are many factors that can affect healthy development, but perhaps none is so devastating in the United States of America as cardiovascular disease (see Appendix A). The term cardiovascular disease refers to a variety of ailments that affect the heart as well as all of the blood vessels in the body. Atherosclerosis is one of these ailments, and is caused by a buildup of plaque in a person‟s arteries; this buildup can accumulate to the point that a clot forms and clogs the artery completely, leading to either a stroke or a heart attack ("What is Cardiovascular Disease (Heart Disease)?", 2013). When atherosclerosis occurs in the heart, it is then called Coronary Artery Disease (CAD) and CAD is the leading cause of death amongst people with heart disease (webmd). Heart disease itself is the leading cause of death in the United States (National Center for Health Statistics, 2013). The causes and prevention of heart disease have been studied for years, and new information is always emerging. For the last several decades, saturated fat and cholesterol have been thought to be major contributors to CAD, and therefore people are typically advised to strictly limit these in their diet (Siri-Tarino, Sun, Hu, & Krauss, 2010). However, recent studies are indicating that it may not be wise to strictly limit the intake of dietary SFAs or replace them with polyunsaturated fatty acids (PUFAs) when taking other health conditions into consideration. Lipids are “. . .oily or fatty biological substances that are not soluble in water. . . (Lawrence, 2010)”. Lipids include fatty acids as well as cholesterol (which is a steroid), and other substances such as fat soluble vitamins. There are two types of fatty acids: saturated and unsaturated. Unsaturated fatty acids are further broken down into two subcategories: polyunsaturated and monounsaturated. Saturated fatty acid molecules have a hydrogen atom for 1 Kelley: Heart Disease Published by ScholarSpace @ JCCC, 2014 each carbon atom in the molecule, hence they are called saturated. Polyunsaturated fatty acid molecules have one carbon to carbon bond (or double bond), meaning that additional hydrogens can be added; monounsaturated fatty acid molecules have two or more double bonds (Lawrence, 2010). Each one of these categories of fat has a different effect on the human body, and there are many sub-categories of fatty acids that fall into each of these three categories. Polyunsaturated fatty acids include both Omega-6 (found mostly in plant sources) and Omega-3 (found mostly in cold-water fish) fatty acids (Lawrence, 2010). It is important to understand these distinctions in order to better understand how dietary fats affect heart disease. Back in the 1800s, cholesterol levels were linked to atherosclerosis, but even after almost 200 years of research, there is still a lot to be learned on this topic, and it is an area of great controversy among scientists and nutrition experts (Lawrence, 2010). Cholesterol is only found in animal sources, and it is also supposed to be limited in the diet since the human body makes its own cholesterol (Allen, 2009). Studies have shown that blood cholesterol level increase of even 1% can put someone at a 2% higher risk of heart disease (DeBakey, 2012). Although High Density Lipoproteins and Low Density Lipoproteins are the two types of cholesterol in the bloodstream that are typically measured by doctors, there are actually five types in the blood; the higher the density, the smaller or more compact the particles of cholesterol are (see Appendix B). Limiting dietary cholesterol can be quite difficult, depending on an individual‟s typical diet. For example, one large egg contains approximately 186 mg of cholesterol (NDL/FNIC Food Composition Database Home Page). This is over half of the recommended daily intake of 300 mg for a healthy person, and almost the entire amount (200 mg) recommended for someone at high risk for heart disease (Dietary Guidelines for Americans, 2010). In addition to low cholesterol consumption, Americans are advised to keep saturated fatty acid consumption as low 2 JCCC Honors Journal, Vol. 5 [2014], Iss. 2, Art. 1 http://scholarspace.jccc.edu/honors_journal/vol5/iss2/1 as possible (at or below 10% of total caloric intake) by substituting saturated fatty acids with polyunsaturated and monounsaturated fatty acids (Hoenselaar, 2012). For individuals at high risk of heart disease, saturated fatty acid consumption is supposed to be restricted to 7% or less of total caloric intake (Smith, et al., 2011; DeBakey, 2012). Reducing saturated fatty acids in the diet has been shown to lower Low-Density Lipoprotein (LDL) cholesterol levels in the blood, which is thought to be important in preventing cardiovascular disease (Smith, et al., 2011). Not only is it important to have low LDL cholesterol in the blood, it has also been shown that the higher the concentration of HDL cholesterol in comparison to LDL cholesterol, the lower a person‟s risk for heart disease (Fogelman, et al., 2011). Americans are typically told to limit red meat and dairy, as these animal products both contain saturated fats. However, a recent study showed that a higher intake of saturated fat from dairy products actually decreases risk of heart disease, while a higher intake of saturated fat from red meat increases risk of heart disease (Otto, et al., 2012). The reason for this is unclear, but it may have something to do with the different fatty acid combinations in milk and meat. This is contrary to current dietary recommendations that discourage consumption of dairy fats altogether in individuals over the age of 2. In addition, this particular study did not find that replacing saturated fatty acid consumption with carbohydrates had any effect on an individuals‟ risk of cardiovascular disease. Another study looked at the different effects of replacing saturated fats with monounsaturated fats versus carbohydrates, and found that either replacement resulted in lower LDL cholesterol, but also lowered HDL cholesterol (Berglund, et al., 2007). As previously mentioned, however, the higher the concentrations of HDL cholesterol in comparison to LDL cholesterol have been shown to lower a person‟s risk for heart disease (Fogelman, et al., 2011). Therefore, simply lowering overall cholesterol may not be the most effective approach to 3 Kelley: Heart Disease Published by ScholarSpace @ JCCC, 2014 reducing risk of cardiovascular disease, unless LDL and HDL serum cholesterol levels are at a good ratio already. Other studies have shown saturated fat consumption to increase overall serum cholesterol, not just LDL, but this is not taken into account when dietary recommendations are being prepared (Hoenselaar, 2012). Although all of these stringent guidelines for dietary cholesterol and saturated fatty acid intake are in place to protect the public from heart disease, not everyone is affected the same way by consuming them (DeBakey, 2012). Some people can eat much higher amounts without a significant increase in blood cholesterol, while others can strictly limit dietary cholesterol and saturated fatty acids but still struggle with high serum cholesterol. Genetics probably account for these differences, and the impact of genes on heart disease is just beginning to be understood. There is one gene that has recently been found to have an impact on the amount of LDL cholesterol that people produce. This gene, PCSK9, has a variation that has been seen to reduce LDL levels (and therefore risk of heart disease) in the people who have it by 40% to 80% (Thanassoulis, 2013). This gene is not alone in its effect on cardiovascular disease, leading us to conclude that an individual‟s true risk cannot be determined without additional research and extensive genetic profiling. There are at least nine genes that, depending on their alleles, have been shown to influence the incidence of heart disease (Yiannakouris, 2012). The polygenic nature of heart disease combined with environmental effects such as diet, exercise, and other factors makes it a very complicated disease and explains why there is so much confusion over the exact cause and the best way to prevent and treat it. One thing that all of the current dietary guidelines fail to mention is the fact that Omega-6 polyunsaturated fatty acids are more likely to contribute to other health complications such as cancer while Omega-3s may have a cancer reducing effect (Lawrence, 2010; de Lorgeril & 4 JCCC Honors Journal, Vol. 5 [2014], Iss. 2, Art. 1 http:/