Eggs and Heart Disease
August 20, 2012
[Eggs and Heart Disease mp3]
What’s the deal with eggs?
It seems that some foods like eggs and margarine are on a perpetual pendulum with the media and, by extension, public opinion. Some days the egg is vilified as a harbinger of heart disease, while other days everything is coming up roses for the little guy. Case in point: Here is a recent article from a local Charleston news station stating
A new study suggests just three egg yolks per week can accelerate heart disease almost as much as smoking.
Recent research has shown that moderate egg consumption—up to one a day—does not increase heart disease risk in healthy individuals and can be part of a healthy diet.
So which is it? Three eggs a week is as bad as smoking or one egg per day is perfectly healthy? It cannot be both. So what should we believe?
As of now the link between serum cholesterol2 and heart disease is about as near to a capital-F Fact as you get in nutrition science. So when you hear that eggs are really high in cholesterol compared with most other foods commonly consumed in the United States, one logical conclusion you could draw from this (if you eat a fair amount of eggs) is the following: If I stop eating eggs I will reduce my risk of heart disease. However, the waters of truth become muddier when you try to examine the actual science behind this bit of conventional wisdom.
Lucky for us my colleague Carrie Dennett did most of the leg work and found the best research available on the subject. What follows is adapted from her research.
- An analysis of data from the Framingham Heart Study in 1982 was one of the first epidemiological studies to suggest that there was no significant association between egg consumption and coronary heart disease (CHD), myocardial infarction, or all-cause mortality.3
- The “Harvard Egg Study” looked at the association between egg consumption and the risk of CHD in two prospective cohorts, the Health Professionals Follow-up Study and the Nurses’ Health Study. After adjustment for age, smoking and other CHD risk factors, there was no significant association between recent or long-term consumption of up to 1 egg per day and risk of CHD or stroke. However, subjects with existing hypercholesterolemia, cardiovascular disease, diabetes, or cancer were excluded from analysis.4
- Djousse and Gaziano examined the association between egg consumption and CVD and total mortality among 21,327 participants from the Physicians’ Health Study I. The authors concluded that consumption of up to 6 eggs per week does not influence the risk of myocardial infarction, stroke, or total mortality in healthy U.S. male physicians.5 Individuals who ate beyond six eggs per week, however, did see an increase in CVD risk.
- Data from the First National Health and Nutrition Examination Survey (NHANES-1) and the NHANES-1 Epidemiological Follow-up Study (NHEFS) was examined and a multivariate analysis found no significant difference in the relative risk of incident stroke, ischemic stroke, coronary artery disease (CAD) and mortality between low (1 egg/week or less), moderate (1-6 eggs/week), and high egg consumers (greater than 6 eggs/week).6 One important exception were high-egg-consuming diabetics who had twice the normal risk of CAD.
- The Japan Public Health Center-based prospective study on cancer and CVD, which involved 90,735 men and women (ages 40-69), found no association between almost daily egg consumption and CHD incidence.7
- Researchers in Spain looked at egg consumption among 14,185 subjects from the prospective cohort participating in the SUN (Seguimiento Universidad de Navarra) Project and found no association between the highest level of egg consumption (greater than 4 eggs/week) and the lowest (less than 1 egg/week).8
All of the above studies suggest that eggs are relatively benign and have little effect on one’s risk of cardiovascular disease. However, there would have to be at least a few that show some detrimental associations of eggs. After all, the well-ingrained idea that eggs are risky business has to be more than just a hunch, right? And indeed there are a handful of such studies.
- Australian Aborigines were followed from 1988-89 to 2002 and it was found that consumption of 2+ eggs per week was associated with a 2.6-fold increased risk of CHD.9
- A prospective study of 10,802 men and women in the United Kingdom found a 2.7-fold increased risk of death among subjects who consumed 6 or more eggs per week.10
However, Carrie notes in the podcast that the authors of the first paper did not collect information on fruit and vegetable intake and thus were unable to determine if there was an inverse association between high fat consumption and low intake of fruits and vegetables. Furthermore, the authors of the second paper used a food frequency questionnaire (FFQ) that was validated only for fiber intake. This means it has been shown that the FFQ they used measures fiber intake fairly accurately, but it has not been proven that it can do the same for other nutrients.
It was noted in the podcast that hyperlipidemic individuals are usually excluded from major studies like these. An exception that we discussed was a randomized, placebo-controlled crossover trial of 40 hyperlipidemic adults by Njike et al.11 Study subjects were randomly assigned to daily consumption of two hardboiled eggs or egg substitute for six weeks, separated by a 4-week washout. They found that egg consumption did not have a detrimental effect on endothelial function or plasma lipids. What was interesting, though, was that the egg substitute group showed a significant improvement in endothelial function, total cholesterol, and LDL cholesterol. Similar results were seen in an identically structured study by Katz et al that used treatment with daily consumption of either two eggs or oats for 6 weeks by 50 healthy men and women (mean age 56 years).12
Carrie also mentioned a study involving hyper- and hyporesponders13 of dietary cholesterol. A randomized crossover trial in Mexico examined the effect of dietary cholesterol from eggs.14 The subjects (30 boys and 30 girls aged 8-12 years) were randomly assigned to eat either two whole eggs or egg substitute for 30 days, with a three-week washout period. Each child was then classified as a hyperresponder or hyporesponder based on their degree of plasma cholesterol response. The hyperresponders had an increase in LDL and HDL cholesterol during the period of whole egg consumption, with the LDL:HDL ratio remaining the same. Hyporesponders had no significant alterations to LDL or HDL.
Of course now we get into even more complicated waters when we include discussions of not just total cholesterol but also LDL:HDL ratios. The previous study even mentions differentiating the small, dense LDL particles from larger, more buoyant LDL particles. There is actually a big difference between the two types, with the former more strongly linked to the heart diseases that we all want to try and avoid. But that is perhaps a topic for another day.
Carrie also brought up the fact that eggs were a major dietary source of choline. However, we were both having some trouble trying to remember what good non-animal sources of choline were available to vegetarians and vegans. Luckily Wikipedia never disappoints.15 Vegans should have no trouble incorporating some of those foods into their diet. Although, on a gram-for-gram basis eggs seem to be a good way to go, otherwise you’ll have to eat an entire pound of spinach to get a similar amount of choline that one egg’ll give ya.
Eating a few eggs a week is not likely to increase your risk of heart disease, especially if you’re already healthy. On the other hand, if you have diabetes or some other metabolic disorder such as hyperlipidemia or hypercholesterolemia you should be mindful of how many eggs you are eating in a given week. You may need to limit your egg consumption to only 1 or 2 per week. In any case, discuss it with your primary physician.
- which is not a fringe journal
- the cholesterol circulating in your blood vessels
- Dawber TR, Nickerson RJ, Brand FN, et al. Eggs, serum cholesterol, and coronary heart disease. The American Journal of Clinical Nutrition 1982;36(4):617-25.
- Hu FB, Stampfer MJ, Rimm EB, et al. A Prospective Study of Egg Consumption and Risk of Cardiovascular Disease in Men and Women. JAMA: The Journal of the American Medical Association 1999;281(15):1387-94.
- Djoussé L, Gaziano JM. Egg consumption in relation to cardiovascular disease and mortality: the Physicians’ Health Study. The American Journal of Clinical Nutrition 2008;87(4):964-9.
- Qureshi A, Suri M, Ahmed S, et al. Regular egg consumption does not increase the risk of stroke and cardiovascular diseases. Med Sci Monitor 2007;13(1):CR1-8.
- Nakamura Y, Iso H, Kita Y, et al. Egg consumption, serum total cholesterol concentrations and coronary heart disease incidence: Japan Public Health Center-based prospective study. British Journal of Nutrition 2006;96(05):921-8.
- Zazpe I, Beunza JJ, Bes-Rastrollo M, et al. Egg consumption and risk of cardiovascular disease in the SUN Project. European Journal of Clinical Nutrition 2011;65(6):676-82.
- Burke V, Zhao Y, Lee AH, et al. Health-related behaviours as predictors of mortality and morbidity in Australian Aborigines. Preventive Medicine 2007;44(2):135-42.
- Mann JI, Appleby PN, Key TJ, et al. Dietary determinants of ischaemic heart disease in health conscious individuals. Heart 1997;78(5):450-5.
- Njike V, Faridi Z, Dutta S, et al. Daily egg consumption in hyperlipidemic adults: Effects on endothelial function and cardiovascular risk. Nutrition Journal 2010;9(28).
- Katz DL, Evans MA, Nawaz H, et al. Egg consumption and endothelial function: a randomized controlled crossover trial. International Journal of Cardiology 2005;99(1):65-70.
- Hyperresonders in this context means those individuals who have an increase in serum cholesterol in proportion to increased dietary cholesterol. Hyporesonders are those individuals that do not see such an increase in serum cholesterol.
- Ballesteros MN, Cabrera RM, del Socorro Saucedo M, et al. Dietary cholesterol does not increase biomarkers for chronic disease in a pediatric population from northern Mexico. The American Journal of Clinical Nutrition 2004;80(4):855-61.
- That’s not true. I’ve been disappointed by Wikipedia a few times.