Posted on 09/05/2012 at 09:45:37 AM by Student BloggerBy Joyanna Hansen
People at risk of heart disease may want to limit their egg yolk consumption, according to a recent study. A team of Canadian researchers investigated the association between egg yolk consumption and arterial plaque in 1,231 individuals, publishing their results last month in Atherosclerosis (1). Researchers concluded that in their study population, egg yolk consumption was associated with arterial plaque buildup, which is a strong predictor of heart disease.
According to the study, total plaque area in patients consuming fewer than 2 egg yolks per week (assessed by a diet questionnaire) was 125 ± 129 mm2 compared with 132 ± 142 mm2 for patients consuming 3 or more egg yolks per week. In further analyses, the researchers divided the subjects into 5 groups based on the number of egg-yolks consumed, and found that “egg-yolk years” (the number of egg yolks consumed per week times number of years consumed) was a significant predictor of arterial plaque after adjusting for the effects of gender, serum total cholesterol, systolic blood pressure, diabetes, body mass index and pack-years of smoking. Comparing egg-yolk consumption to smoking pack-years, the authors concluded that effect of egg yolks on plaque formation was approximately two-thirds that of smoking.
Factors to consider
Although the results of this study are intriguing, there are a few reasons to hesitate before running out to the grocery store for some egg substitute. First of all, this was a cross-sectional, observational study, meaning that it was designed to look at statistical associations between an exposure, such as egg yolk consumption, and an outcome, such as arterial plaque, at a single time point. In order to understand whether egg yolk consumption alone leads to plaque formation, researchers would have to measure egg yolk consumption as well as plaque formation at several time points. So, although an association between egg yolks and artery plaque was observed, it's not clear if egg yolks were the causal factor.
Secondly, this study did not take into account all the other aspects of the study participants' diets. People eat meals, not single foods, and the aggregate effect of a dietary pattern may be more important to overall health than consumption of a single food item such as eggs yolks. Interestingly, the authors did not adjust for the effects of saturated fat consumption or total dietary cholesterol consumption. It's possible that the combination of egg yolk consumption and high saturated fat or dietary cholesterol consumption (eggs and bacon, anyone?) is associated with arterial plague, rather than egg yolks alone. Unfortunately, this study did not ask about consumption of other foods, and so the question of how overall dietary pattern is related to arterial plaque in this population is unanswered.
Finally, researchers didn't have information on lifestyle factors like exercise; this is another factor that could affect the observed association between egg yolk consumption and arterial plaque formation.
This study has ignited controversy as previous research has shown no link between moderate egg yolk consumption and heart disease (2). More research is needed to further understand if there is an egg yolk-heart disease link; as with most foods, it's likely that moderation is key!
1. Spence, J. D., D. J. Jenkins, et al. (2012). "Egg yolk consumption and carotid plaque." Atherosclerosis.
2. Djousse, L. and J. M. Gaziano (2008). "Egg consumption and risk of heart failure in the Physicians' Health Study." Circulation 117(4): 512-516.