Cardiovascular disease is caused by the progressive narrowing of arteries, which is termed atherosclerosis. Atherosclerotic disease in the coronary arteries of the heart and the cerebral arteries of the brain can lead to heart attack and stroke, respectively. In the peripheral arteries of the legs, atherosclerosis can lead to peripheral arterial disease which can lead to claudication or pain with walking in the legs. The atherosclerotic process worsens with age, but there are several factors which are known to accelerate the narrowing of arteries. The major traditional risk factors for cardiovascular disease include smoking, high blood pressure, diabetes, and high cholesterol. There are several other factors which can hasten the atherosclerotic process including diets high is saturated fat. Fortunately, most of the risk factors for cardiovascular disease and atherosclerosis can be changed or modified by healthy lifestyles and regular exercise. In the past, egg yolks were considered to contain high amounts of cholesterol and thus were thought to be unhealthy. This theory has remained controversial, and more recent research has shown that egg yolks in moderation can be part of a heart healthy diet.
Researchers, lead by Dr. J. David Spencer of the Western University in Canada, have found that eating egg yolks can accelerate the atherosclerotic process similarly to about two-thirds of the effect of smoking. The results of their research were published online in the journal Atherosclerosis. The investigators performed their study on 1,262 individuals with a mean age of 61.5 years who were attending vascular prevention clinic at London Health Sciences Centre’s University Hospital. The study participants had carotid artery plaque area measured by duplex ultrasound and were interviewed on their lifestyle, including smoking history and egg yolk consumption. The carotid artery is one of the main arteries that supplies blood to the brain from the heart and plaque buildup in this artery can increase risk of stroke and is an indication of overall cardiovascular disease and atherosclerosis. The researchers found that carotid plaque area increased linearly with age after the age of 40 years, but increased exponentially with both smoking and egg yolk consumption. This finding was particularly evident in those individuals who ate three or more eggs per week. The researchers concluded that egg yolk consumption makes carotid artery plaque build up about two-thirds as much as smoking.
The authors wrote, “We conclude that the prevailing tendency to ignore dietary cholesterol as a risk factor for coronary heart disease requires reassessment, including the consumption of cholesterol from eggs. Although low fat egg dishes may be less harmful than meals high in both saturated fat and cholesterol (even if the latter have somewhat lower cholesterol content), meals high in cholesterol should not be consumed regularly by those at risk for cardiovascular diseases, as dietary cholesterol itself is harmful, and potentiates the effect of saturated fats… Our study supports a return to earlier concepts of the therapeutic diet, including a continued prohibition on high dietary cholesterol intakes”. The authors finalized their recommendations by writing, “Our findings suggest that regular consumption of egg yolk should be avoided by persons at risk of cardiovascular disease. This hypothesis should be tested in a prospective study with more detailed information about diet, and other possible confounders such as exercise and waist circumference”.
This study raises an important question: Are egg yolks as bad for your health as smoking? The study authors would say ‘yes’ but others have disagreed. The key to this question is the cholesterol content of the egg yolks. High blood cholesterol levels, particularly low density lipoprotein (LDL) cholesterol, are a known risk factor for cardiovascular disease, but do egg yolks contain enough cholesterol to raise blood levels to a dangerous level. This question has been addressed ad nauseam in the past, and it has been concluded that egg yolk consumption in moderation can be part of a heart healthy diet. This study has a number of weaknesses and these include the fact that several confounders, such as exercise level and waist circumference, were not taken into consideration. In addition, the study relied on participants to recall the amount of egg yolks consumed in the past and only included those individuals with already existent cardiovascular disease. The National Heart Blood and Lung Institute has recommended that cholesterol intake should be limited to no more that 300 mg per day (slightly more that one egg yolk), and to eat no more that four whole eggs per week. Those individuals who have diabetes, high cholesterol, high blood pressure, heart disease, or who have had a stroke should limit their daily cholesterol intake to 200 mg per day. More research is needed to address the concerns raised in this study, but prior research has shown that egg yolks in moderation provide more health benefits than risks.
J. David Spencer, David J.A. Jenkins, Jean Davignon “Egg yolk consumption and carotid plaque” Atherosclerosis – 10 August 2012 (10.1016/j.atherosclerosis.2012.07.032)