Red Meat Consumption Association with Cardiovascular Disease

Last fall I was tasked with writing a term paper for my Principles of Physiology class on any topic related to physiology of my choosing.  I had the idea of writing something about the health impacts of eating meat, due to the connection between meat consumption and the many environmental and ethical issues related to its production.  Upon doing a bit of research, I realized that eating certain types of meat has known connections with the leading cause of death in the world, cardiovascular disease.  So, essentially, not only does meat contribute to some of the worst environmental problems in the world, but also to some of the worst health problems.  

The resulting paper, found below, details the evidence for the connection between red meat consumption (the type of meat most commonly implicated) and cardiovascular disease, and the physiological mechanisms proposed for the cause.  The results are just one more reason why cutting meat from your diet is a responsible decision.  

Red Meat Consumption Association with Cardiovascular Disease

Introduction

            According to the World Health Organization, cardiovascular-related diseases are the leading cause of death in the world, based on deaths due to ischaemic heart disease and stroke.  In 2015, ischaemic heart disease accounted for 8.76 million deaths worldwide, more than any other single factor.  Stroke followed as the second largest factor, with 6.24 million deaths.  Together these two factors accounted for approximately 27 percent of total global mortality (1).  In 2015, diseases of the heart was similarly the leading cause of death in the United States with 23.4 percent of total deaths, while stroke was ranked as the fifth leading cause with 5.2 percent of deaths (2). 

            Although there are many factors that likely contribute to the development of cardiovascular diseases in individuals, diet is a major factor that has often been implicated in affecting one’s risk.  This is particularly true in Western countries, such as the United States, where the so called “Western diet” of high fat and processed food has been linked to high prevalence of cardiovascular and other diseases.  One specific characteristic of this diet is high intake of red meat (3).  Unlike white meat and fish, red meat consumption is often associated with risk of developing cardiovascular diseases (4).  Coronary (ischaemic) heart disease is one type of cardiovascular disease that has seen particular association with red meat consumption in studies (3), but other conditions have also been linked, including stroke (5), and hypertension (6).  Understanding the risks of developing these diseases associated with consuming red meat, as well as the physiological mechanisms through which regular consumption of red meat may lead to cardiovascular diseases is important from both a scientific and general dietary perspective, especially in light of the high rate of cardiovascular disease-related mortality and high red meat consumption seen in today’s society.  These issues are analyzed here based on current research and established physiological knowledge.                                        

Evidence of Association

            Association between red meat consumption and various types of cardiovascular disease has been observed in numerous prospective cohort-based and case-control studies.  Red meat typically refers to most meat from mammals, such as beef, pork, lamb, or mammalian game, and excludes poultry and fish (7).

            One form of cardiovascular disease in particular that has drawn associations with red meat is coronary heart disease.  Micha et al. conducted a review and meta-analysis of 20 prospective cohort and case-control studies that assessed the risk of eating meat on developing cardiovascular disease.  Based on four studies that assessed risk of consuming unprocessed red meat on developing coronary heart disease, there was no association found.  However, an analysis of five studies that assessed risk of consuming processed meat revealed a 42 percent greater risk of developing coronary heart disease per each serving in a day.  This processed meat included any preserved meat treated by smoking, curing, or salting and any meat with added chemical preservatives, however this was mainly restricted to red meats (7).  Despite this study not finding an association between unprocessed red meat consumption and coronary heart disease, the fact that consuming processed red meat was instead likely to have a link is still particularly significant, as much of meat consumption in Western culture today such as in the United States is of processed meats (3). 

            Another type of cardiovascular disease that has been associated with red meat consumption is stroke.  Micha et al. did not find an association between either unprocessed red meat consumption or processed meat consumption, although this was only based on a review of three studies (7).  Chen at al. performed a review and meta-analysis of five prospective cohort studies assessing relation between unprocessed red meat and processed meat consumption and risk of stroke, and found an overall association between both unprocessed red meat and processed meat and risk of stroke.  Here, again, “processed meat” consisted largely of red meat.  Based on a dose-response analysis, it was found that risk of stroke increased 13 percent for each 100 gram per day increase for unprocessed red meat consumption, and 11 percent for each 50 gram per day increase in processed meat consumption (5).                   

                        Another cardiovascular condition which has been seen to be positively associated with red meat consumption is hypertension.  Hypertension is a major risk factor for other cardiovascular diseases, including coronary heart disease and stroke, so determining risk factors for this has been of great concern for researchers.  One example of the connection that has been found between red meat and hypertension includes results from the Coronary Artery Risk Development in Young Adults (CARDIA) Study, a 15 year prospective cohort study of 4304 men and women ages 18 to 30 years old at baseline. In this study, higher consumption of both unprocessed red meat and processed meat among individuals way seen to result in a significantly greater incidence of high blood pressure.  This was true even after adjusting for factors including demographics, lifestyle, and other dietary factors (6).  In another prospective cohort study of an older subset of individuals (men aged 41-57 at experiment baseline) performed over seven years, a positive association was also seen between red meat consumption and increase in blood pressure (8).             

Physiological Mechanisms

            There are many factors that may contribute to the development of cardiovascular diseases, as well as a number of mechanisms that have been proposed as potential explanations for how consumption of red meat may contribute to the development of these diseases.  A common theme seen in many of these explanations, however, is the narrowing of the arteries.  There are several factors related to eating red meat that may contribute to this (7).        

            The primary factor cited as a likely explanation for red meat’s contribution to cardiovascular disease is the high saturated fat and LDL cholesterol content in red meat (7).  LDL cholesterol, sometimes referred to as “bad cholesterol”, is a form of cholesterol that often can lead to negative health effects when existing at raised levels in the body.  Saturated fat increases the production of LDL cholesterol, and so when ingested at high levels this raises LDL cholesterol concentration in the blood, along with consuming it directly.  When LDL cholesterol is at a high concentration in the blood, it can combine with other materials to form a thick substance called plaque that sticks to the walls of the arteries, thereby narrowing the passageway through these vessels, and making it harder for blood to flow through.  This condition, known as atherosclerosis, can lead to a number of health problems, including those cardiovascular diseases discussed above (9).

            There most obvious of the conditions discussed that can be caused by atherosclerosis is hypertension.  As the arteries narrow from plaque build-up, the body still tries to pump blood through them at a normal rate.  This same volume of blood trying to squeeze through a smaller space means that blood is pushing harder against the walls of the artery, increasing pressure within the vessel.  Hypertension is defined by an elevated pressure in the arteries (9). 

            Many of the conditions that lead to hypertension, including atherosclerosis, also contribute to other cardiovascular problems.  One of the most serious of these is coronary heart disease.  Coronary heart disease occurs when there is obstruction in the coronary arteries, which provide blood flow to the tissues of the heart.  Intuitively, atherosclerosis can be a major contributor to this, as the plaques in on the artery walls prevent normal flow through the vessels.  Serious problems can occur from the obstruction that occurs in coronary heart disease, including myocardial infarction, or heart attack.  A heart attack occurs when a coronary artery somewhere in the heart becomes completely occluded, prohibiting flow of blood that the heart need to function.  This is most often occurs when a clot in the artery blocks the flow of blood, but the narrowing of the vessel due to atherosclerosis greatly increases the chance of this occurring (9).

            The impact of atherosclerosis on stroke occurs by much the same mechanism.  A stroke occurs when there is insufficient blood flow provided to the brain, such as due to occlusion of a cerebral artery.  Just like in the heart, these arteries can become narrowed by build-up of plaques, and if complete occlusion occurs, a stroke will take place (9).

            The mechanisms described above detail how high intake of saturated fats and LDL cholesterol from regular consumption of red meat may contribute to various cardiovascular diseases.  Another possible explanation that may contribute in addition to this is the high sodium and nitrate content found in processed red meats.  Large amounts of salt and nitrates are often added in processed meats to help preserve them, and in the case of salt for added taste.  These substances have a number of effects that contribute to narrowing of the arteries.  Sodium from salt in food directly contributes to raising blood pressure, and also may increase stiffness of blood vessels, making them harder to expand as blood flows through them.  Nitrates have been seen to contribute to atherosclerosis and vascular dysfunction.  All of these effects have the similar result of decreasing the area through which blood can flow through the arteries and increasing the risk of the cardiovascular diseases mentioned above (7).  Decreased radius in the arteries increases resistance and thus pressure, leading to hypertension.  It also increases difficulty for blood flowing through the coronary arteries and cerebral arteries, increasing risk of coronary heart disease, heart attack, and stroke (9).  This mechanism may also explain why higher incidence of coronary heart disease was seen in some studies for consumption of processed red meat that for unprocessed red meat (7).

            Evidence for some other proposed mechanisms through which red meat consumption may contribute to development of cardiovascular disease has been found.  One of these proposed mechanisms is by effects of iron intake that occurs through red meat consumption.  Heme iron, a type of iron found only in meat, has been linked to increased risk of coronary heart disease.  An explanation for this is that heme iron may catalyze oxidation of LDL cholesterol, leading to atherosclerosis.  A meta-analysis conducted by Hunnicutt et al. of studies looking at the potential coronary heart disease risk of different types of iron, heme iron was found to increase risk, while nonheme iron from plant and other non-meat sources did not (10).  Other studies have implicated the metabolism of a particular nutrient found in red meat, L-carnitine, by microbiota in the intestines as another potential contributor to cardiovascular disease.  This intestinal microbiota metabolism has been found to increase atherosclerosis in mice, suggesting a similar effect in humans (11).  Both of these proposed mechanisms, through their potential to incite atherosclerosis, thereby narrowing the passageway of the arteries, have the potential to increase risk of hypertension, coronary heart disease, stroke, and other cardiovascular diseases (9).                        

                                               

Conclusions

            Cardiovascular disease, representing the number one cause of death in the world, is a major human health problem facing societies throughout the globe (1).  This is especially true in Western countries, such as the United States, where a diet of high fat, processed foods has been implicated in the prevalence of cardiovascular diseases.  Red meat is one particular, highly consumed staple of this diet (3).  Numerous prospective cohort and case-control studies of individuals with varying levels of red meat consumption have found positive associations between red meat intake and incidence of cardiovascular disease, including coronary heart disease (7), stroke (5), and hypertension (6,8).  A variety of mechanisms have been proposed to explain these associations, including the high saturated fat and LDL cholesterol content of red meat producing atherosclerosis in the arteries, and the effects of sodium and nitrates in processed red meat on the arteries (7).  These mechanisms share the common theme, however, of narrowing of the arteries, a hallmark of cardiovascular disease which contributes to many serious conditions (9).                   

            There are a variety of factors that may contribute to development of cardiovascular disease, including consumption of other foods that are high in fat, cholesterol, or sodium (9).  Consumption of red meat is only one particular factor that may play a contributing role towards this.  However, a review of the literature surrounding red meat’s potential to contribute to cardiovascular disease reveals that eating this type of meat poses a significant and well documented risk towards this end.  This is particularly true for processed red meat, which carries the added risk of consuming preservatives it is treated with, such as high amounts of sodium (7).  The risk of consuming red meat is particularly highlighted by the contrast with the studied effects of eating other types of meat, such as poultry and fish, which have not shown this type of risk (4).  Numerous studies have shown the benefits of eating plant-based diets that are high in fruits, vegetables, nuts, and whole grains on prevention of many chronic diseases, including cardiovascular diseases (12).  Reducing red meat consumption may be one particularly important step that can be taken to move towards this seemingly healthier diet.    

References

1.      World Health Organization. Top 10 causes of death. 2017. Retrieved from http://www.who.int/mediacentre/factsheets/fs310/en/  

2.      National Center for Health Statistics. Health, United States, 2016: With Chartbook on Long-Term Trends in Health. 2017. 

3.      Hu F.B., Rimm E.B., Stampfer M.J., Ascherio A., Spiegelman D., Willett W.C. Prospective study of major dietary patterns and risk of coronary heart disease in men. Am J Clin Nutr 2000;72:912-921.

4.      Hu F.B., Stampfer M.J., Manson J.E., Ascherio A., Colditz G.A., Speizer F.E., Hennekens C.H., Willett W.C. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr 1999;70:1001-1008.

5.      Chen G.C., Ly D.B., Pang Z., Lui Q.F. Red and processed meat consumption and risk of stroke: a meta-analysis of prospective cohort studies. Euro J Clin Nutr 2013;67:91-95.

6.      Steffen L.M., Kroenke C.H., Yu X., Pereira M.A., Slattery M.L., Van Horn L., Gross M.D., Jacobs D.R.  Associations of plant food, dairy product, and meat intakes with 15-y incidence of elevated blood pressure in young black and white adults: the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Am J Clin Nutr 2005;82:1169-1177.

7.      Micha R., Wallace S.K., Mozaffarian D. Red and Processed Meat Consumption and Risk of Incident Coronary Heart Disease, Stroke, and Diabetes Mellitus. Circulation 2010; 121:2271-2283.

8.      Miura K., Greenland P., Stamler J., Liu K., Daviglus M.L., Makagawa H. Relation of vegetable, fruit, and meat intake to 7-year blood pressure change in middle-aged men: the Chicago Western Electric Study. Am J Epidemiol 2004;159:572–80.

9.      Widmaier, E.P., Raff, H., Strang, K.T. Vander’s Human Physiology. 12^th ed. McGraw Hill; 2011. p. 421-427.

10.  Hunnicutt, J., He, K., Xun, P. Dietary iron intake and body iron stores are associated with risk of coronary heart disease in a meta-analysis of prospective cohort studies. J Nutr 2014;144:354-366. 

11.  Koeth, R.A., Wang, Z., Levison, B.S., Buffa, J.A., Org, E., Sheehy, B.T., Britt, E.B., Fu, X., Wu, Y., Li, L., Smith, J.D., DiDonato, J.A., Chen, J., Li, H., Wu, G.D., Lewis, J. D., Warrier, M., Brown, J.M.,  Krauss, R.M., Wilson Tang, W.H., Bushman, F.D., Lusis, A.J., Hazen, S.L. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nature Medicine 2013;19:576-585.    

12.  Hu, F.B. Plant-based foods and prevention of cardiovascular disease: an overview. Am J Clin Nutr 2003;78:5445-5515.