Eggs and the Connection to Cardiovascular Disease
Eggs and the Connection to Cardiovascular Disease
Joy Stepinski, MSN, RN-BC
March 15, 2023
Introduction
Eggs are not only a favorite breakfast food for many people, but also an important ingredient in baking tasty treats like cakes and pies. While some research rings the alarm on the health benefits that eggs fail to achieve, others make claims that eggs provide important nutrients. For the purpose of this discussion, let’s take both sides into consideration.
According to one review [1], a single large egg yolk contains 215 to 275 mg of cholesterol. To put this into perspective, the authors compare one yolk to the 210 mg of cholesterol contained in a Hardee’s Monster Thickburger, comprised of beef, cheese, and bacon. Prior to 2015, dietary guidelines advised that Americans should limit dietary cholesterol to less than 300 mg per day [2]. Therefore, just one single egg nearly met that number. New dietary guidelines since 2015 no longer provide an amount in which Americans should follow. However, they do heed the warning that “The National Academies recommends trans-fat and dietary cholesterol to be as low as possible without compromising the nutritional adequacy of the diet” [3].
To read further about cholesterol, be sure to check out the article called “A Close Look at Cholesterol” in the Article Library. Cholesterol is needed by the body, but the liver synthesizes all the cholesterol that is required without outside sources. The rest is obtained as a result of lifestyle factors and especially dietary intake, primarily in the form of animal products. When an overabundance of cholesterol is available, people are much more prone to atherosclerotic plaques.
Dietary Guidelines
Perhaps this change in the dietary guidelines should be untangled before continuing on with this discussion. The original wording of the 2015 guidelines stated, “cholesterol is not considered a nutrient of concern for overconsumption” [4] which drastically changed a prior suggested cholesterol limit from 300 mg per day to none at all and disregarded any dietary cholesterol harm. As a result, the Physicians Committee for Responsible Medicine (PCRM) filed a lawsuit in 2016 [5] against the U.S. Department of Agriculture, as well as the Department of Health and Human Services. The lawsuit raised the concern that the Dietary Guidelines Advisory Committee violated the Federal Advisory Committee Act, which specifically stated that committees would not be influenced by the appointing authority or special interest groups. According to documents the PCRM received as a result of the Freedom of Information Act, the American Egg Board nominated one member to the Dietary Guidelines Advisory Committee. A second member received egg-industry research grants, and two others were employed by universities that received money from the American Egg Board to challenge cholesterol limits. The mission of the American Egg Board is “to support America’s egg farmers and increase demand for eggs and egg products” [6]. Thus, the new statement was the result of a committee that was completely biased and influenced by the special interest group. After a year of pressure, revised guidelines were released, which stated that as little cholesterol as possible should be consumed [7].
Concern for the Effect of Eggs on the Heart
Spence and coauthors [1] discuss some important points in their review. Often healthcare professionals are interested in the fasting cholesterol blood level. However, the food consumption should not merely be about a fasting level. For the majority of the day, humans are in a non-fasting state. In other words, sugar, fat, and cholesterol are consumed during the waking hours. Yet the implications are even more important. Foods can lead to oxidative stress and inflammation, which can impair the arteries. Furthermore, although cholesterol-lowering statin medication is frequently claimed to lower fasting cholesterol, these drugs are not the magic answer. Diet accounts for 85% of cardiovascular disease risk, and even with a statin, studies show that there is still upwards of 70% risk.
Dietary cholesterol plays a big role in harming the arteries, and patients with cardiovascular disease should particularly limit this intake. In fact, separate research cited by the review found that a single high-fat meal transiently impairs endothelial function [8]. The endothelium refers to the inner lining of the arteries. The authors shared additional research [1] showing the dietary effect on people consuming a low cholesterol diet. Following egg yolk consumption, fasting cholesterol was raised by 40 mg/dL. Another study found a 12% increase in LDL (low density lipoprotein) cholesterol. The authors warn caution to studies that claim benefits of eggs, the eagerness of media to report this information, and the lack of robust data that actually proves this hypothesis.
A study from 1984 [9] likewise demonstrated the effect of egg consumption on LDL cholesterol. The research investigated the effect of eating one extra-large egg on college students for three weeks. The number of lacto-vegetarian participants was small (n = 17) in this random double blind crossover trial. However, the results indicated that the egg ingestion increased dietary cholesterol from 97 to 418 mg per day. Mean plasma LDL cholesterol increased by 12% when eggs were consumed, compared to the time period of not consuming eggs.
In a separate study [10], researchers set out to determine the correlation between dietary cholesterol and egg consumption upon incident cardiovascular disease and all-cause mortality. The research collected data from individual participants among six prospective US cohorts between 1985 and 2016, and included 29,615 subjects. The study examined the food that participants were consuming. This was converted into a measurement that involved the estimated number of consumptions in a certain time range. The research investigated the outcome of incident cardiovascular disease, such as coronary heart disease, stroke, heart failure, and death related to heart disease. The authors took into consideration the association of dietary cholesterol, including eggs, processed meat, unprocessed meat, and total dairy products. Egg intake with respect to dietary cholesterol was further adjusted.
The median participant follow-up was 17.5 years. Results showed that mean dietary cholesterol intake was 285 mg per day and overall mean egg consumption was 0.34 per day. Upon the study conclusion, there were 5,400 cardiovascular disease events and 6,132 deaths. The research discovered that for each 300 mg of dietary cholesterol consumed per day, there was a higher risk of incident cardiovascular disease. The authors also concluded that for each additional half egg consumed, there was a significantly higher risk of incident cardiovascular disease. The overall conclusions were that higher consumption of dietary cholesterol or eggs was significantly associated with higher incident cardiovascular disease and all-cause mortality. These findings were dose-dependent. When the authors adjusted for variables, they were not able to determine if cholesterol from certain foods were more harmful than others. However, they noted that 25% of egg consumption contributed to the total dietary cholesterol intake. “Findings of the current study suggest that cholesterol from egg yolk may be harmful in the context of the current US diet, in which overnutrition and obesity/overweight are more common than malnutrition and underweight” (p. 1094).
Another study examined whether consumption of egg and cholesterol played a role in cardiovascular health [11]. This research used 567,169 participants from surveys mailed to homes through an NIH-AARP study in 1995 – 1996. A food frequency questionnaire (FFQ) was completed by the subjects. The authors noted that at baseline, people who reported higher egg consumption also had higher cholesterol and higher red meat intake, were less physically active, and were less inclined to consume fruit. The subjects were followed for 16 years. Upon conclusion of the study, 129,328 deaths occurred. The research concluded that whole egg consumption led to higher all-cause mortality, which included both heart disease and cancer. The authors reported that each additional 300 mg of daily dietary cholesterol was correlated with a 16% increased risk of cardiovascular mortality and 24% higher risk of cancer mortality. On the other hand, egg white consumption did not appear to cause a significant role in cardiovascular disease. More on egg whites later.
Coronary artery calcification (CAC) is characterized by calcium deposits in the atherosclerotic plaques. A published research study by Bruscato and colleagues had determined the relationship between saturated fatty acid consumption and CAC. For every 1% increase in saturated fatty acids, there was an 8% increase in prevalence of CAC. Saturated fatty acids are found in animal foods like meat and dairy products, tropical oils like palm and coconut, and processed food [12]. In a South Korean study, [13] scientists investigated the connection between eggs and CAC as a sign of heart disease. This was a cross-sectional study that used 23,417 participants. The subjects did not have a baseline cardiac history and completed a food frequency questionnaire to document their food intake. The researchers compared people who ate at least 7 eggs per week to those who consumed less than 1 egg per week. The results concluded that eggs appeared to be related to signs of coronary atherosclerosis. Higher CAC scores in general correlated with people who ate a low number of vegetables and had a higher BMI. These findings are similar to the Bruscato research that higher intake of carbohydrates led to a lower CAC score [12].
The Case Supporting Eggs as a Health Food
One study supporting egg consumption is a highly publicized research article published in Heart [14]. This Chinese study examined the egg intake of the enrolled 461,213 adults. Their findings showed that 13.1% of participants reported daily consumption and 9.1% reported never or rare consumption. The conclusions were that daily consumers had an 18% lower risk of mortality related to heart disease and a 28% lower risk of hemorrhagic death compared with non-consumers. Limitations of the study are noteworthy. The authors indicated that a small portion of the subjects were contacted for follow-up. Additionally, they excluded cases or deaths that occurred within the first 2 years of the study initiation to make their results appear more robust. However, these are the events that would be most important. The accuracy of the follow-up data is questionable, considering that not the full number of subjects participated and lack of imperative data occurred.
Another large well-known meta-analysis published research in the British Medical Journal concluded that higher consumption of eggs is not associated with increased risk of coronary heart disease or stroke [15]. The authors selected 8 articles, totaling 17 reports on the effects of eggs. Their conclusions were that higher consumption of egg was not related to increased risk of heart disease or stroke. However, they relate that diabetic patients are at increased risk of coronary heart disease. Upon scrutiny of this analysis, the authors described that they used 6 articles to create their position on the role of egg consumption on heart disease. At least one of these studies [16] was funded by the Egg Nutrition Center, which is the science and nutrition education division of the American Egg Board. Other limitations were outlined by the authors. There likely was misreporting of intake. Egg consumption was assessed via self-reported food frequency questionnaires, like some of the studies above. This may result in self-bias. During the follow-up participants may have changed their diets. Apart from these reported issues, there was little information outlining the overall dietary pattern of the subjects.
A Note About Egg Whites
Although egg whites contain less cholesterol, this does not mean that they are actually “heart-healthy.” Egg whites are comprised of 3% fat, 6% carbohydrates, and 91% protein [17]. As established by the China Study [18], fat intake among the Chinese people was less than half of that of Americans during the time period of the study. Animal protein intake was a miniscule portion of what Americans consumed, at just 10%. The research showed that serum cholesterol was directly related to dietary fat, animal protein, and meat, and inversely associated with dietary fiber and legumes. As pointed out by Levin [19], egg whites contain a concentrated source of animal protein. Therefore, they are not a contributor to an optimal nutritious diet.
Conclusion
Delving into this research on eggs, several observations can be made. (1) Most of these studies relied on self-reported dietary data. This in itself can lead to some bias, as people often do not remember the foods they consume and may not report accurate intake. (2) People consume a wide variety of food. If intake consists of both eggs and meat, extrapolating which source the cholesterol originated may not be very feasible. (3) In general, the research seemed to indicate that people who consumed more eggs also consumed more meat [10]. (4) Eggs and meat are both known to contain high amounts of dietary cholesterol [10]. (5) When consuming low amounts of dietary cholesterol, consuming eggs can raise cholesterol [1, 9]. (7) Dietary cholesterol is associated with primarily animal food intake, and its disease ramifications have been established through extensive research in the China Study [18] where researchers found that coronary artery disease risk increased with animal foods, yet decreased with plant-foods. (8) Information on the positive health impact of eggs may be strongly influenced by people who are directly or indirectly funded by the American Egg Board [1, 4], as well as the media.
When thinking about the purpose of eggs, they were created to provide life to a baby chick [19]. Eggs hold the exact package needed to create a being with feathers, a beak, and wings. They were not naturally designed for human consumption, and further research suggests that they may be connected to other diseases, such as cancer and diabetes [11, 15, 19], in addition to heart disease. The overall message is that there is a large amount of dietary cholesterol in eggs, and dietary cholesterol is directly related to heart disease. Minimizing the intake of dietary cholesterol, such as eggs, is an important health strategy. Eggs may be included in the recommended 2 – 3 servings of organic meat per week. However, people with diagnosed heart disease would want to consider further reducing cholesterol intake and eliminating eggs from their diet. (Note: Egg replacement information may be found in the Educational Resources section of the website.)
References
1. Spence, J. D., Jenkins, D. J., & Davignon, J. (2010). Dietary cholesterol and egg yolks: not for patients at risk of vascular disease. Canadian Journal of Cardiology, 26(9), e336-e339. https://doi.org/10.1016/s0828-282x(10)70456-6
2. Sollid, K. (2015). New dietary guidelines: What changed & what stayed the same. https://foodinsight.org/new-dietary-guidelines-what-changed-what-stayed-the-same/
3. USDA. (2020). Dietary guidelines for Americans 2020 – 2025. https://www.dietaryguidelines.gov/sites/default/files/2021-03/Dietary_Guidelines_for_Americans-2020-2025.pdf
4. Williams Sr, K. A., Krause, A. J., Shearer, S., & Devries, S. (2015). The 2015 dietary guidelines advisory committee report concerning dietary cholesterol. The American Journal of Cardiology, 116(9), 1479-1480. https://doi.org/10.1016/j.amjcard.2015.07.077
5. Physicians Committee for Responsible Medicine. (2016). The Physicians Committee praises new dietary guidelines for strengthening cholesterol warnings, but demands investigation into cholesterol money trail. https://www.pcrm.org/news/news-releases/physicians-committee-praises-new-dietary-guidelines-strengthening-cholesterol
6. American Egg Board. (2023). About us. https://www.incredibleegg.org/about-us/
7. Levin, S. (2019). The dangers of industry-influenced nutrition research. Physicians Committee for Responsible Medicine. https://www.pcrm.org/news/blog/dangers-industry-influenced-nutrition-research
8. Vogel, R. A., Corretti, M. C., & Plotnick, G. D. (1997). Effect of a single high-fat meal on endothelial function in healthy subjects. The American Journal of Cardiology, 79(3), 350-354. https://doi.org/10.1016/S0002-9149(96)00760-6
9. Sacks, F., Miller, L., Sutherland, M., Albers, J., Salazar, J., Foster, J., ... & Kass, E. (1984). Ingestion of egg raises plasma low density lipoproteins in free-living subjects. The Lancet, 323(8378), 647-649.
10. Zhong, V. W., Van Horn, L., Cornelis, M. C., Wilkins, J. T., Ning, H., Carnethon, M. R., ... & Allen, N. B. (2019). Associations of dietary cholesterol or egg consumption with incident cardiovascular disease and mortality. JAMA, 321(11), 1081-1095. https://doi.org/10.1001/jama.2019.1572
11. Zhuang, P., Wu, F., Mao, L., Zhu, F., Zhang, Y., Chen, X., ... & Zhang, Y. (2021). Egg and cholesterol consumption and mortality from cardiovascular and different causes in the United States: a population-based cohort study. PLoS Medicine, 18(2), e1003508. https://doi.org/10.1371/journal.pmed.1003508
12. Bruscato, N. M., da Luz, P. L., Werle, B. M., Schvartzman, P. R., Kesties, J., Vivian, L., ... & Moriguchi, E. H. (2021). Coronary artery calcification and dietary intake in asymptomatic men. Brazilian Journal of Medical and Biological Research, 54. https://doi.org/10.1590/1414-431X2021e11371
13. Choi, Y., Chang, Y., Lee, J. E., Chun, S., Cho, J., Sung, E., ... & Guallar, E. (2015). Egg consumption and coronary artery calcification in asymptomatic men and women. Atherosclerosis, 241(2), 305-312. https://doi.org/10.1016/j.atherosclerosis.2015.05.036
14. Qin, C., Lv, J., Guo, Y., Bian, Z., Si, J., Yang, L., Chen, Y., Zhou, Y., Zhang, H., Liu, J., Chen, J., Chen, Z., Yu, C., Li, L., & China Kadoorie Biobank Collaborative Group (2018). Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults. Heart (British Cardiac Society), 104(21), 1756–1763. https://doi.org/10.1136/heartjnl-2017-312651
15. Rong, Y., Chen, L., Zhu, T., Song, Y., Yu, M., Shan, Z., ... & Liu, L. (2013). Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. BMJ, 346, e8539. https://doi.org/10.1136/bmj.e8539
16. Scrafford, C. G., Tran, N. L., Barraj, L. M., & Mink, P. J. (2011). Egg consumption and CHD and stroke mortality: A prospective study of US adults. Public Health Nutrition, 14(2), 261-270. https://doi.org/10.1017/S1368980010001874
17. fatsecret. (2023). Egg white. https://www.fatsecret.com/calories-nutrition/usda/egg-white
18. Campbell, T. C., Parpia, B., & Chen, J. (1998). Diet, lifestyle, and the etiology of coronary artery disease: the Cornell China study. The American Journal of Cardiology, 82(10), 18-21. https://doi.org/10.1016/S0002-9149(98)00718-8
19. Levin, S. (2013). What’s wrong with eggs? Forks Over Knives. https://www.forksoverknives.com/wellness/whats-wrong-with-eggs/