The British Medical Journal Heart recently published this eye-catching article: “Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults.”^[1] It sure is an impressive title—over 500,000 Chinese adults!—but what can we learn from the study?

The study’s surprising conclusion that consumption of up to one egg per day was associated with a lower risk of heart disease sparked considerable excitement, as illustrated by headlines around the world:

• “An egg a day to keep the doctor away?” (BBC)
• “An egg a day could keep the doctor away, research suggests” (The Daily Mail)
• “Eating an egg a day may keep heart disease away, a new study says” (Time)
• “Daily egg consumption may reduce cardiovascular disease” (EurekAlert)
• “Eggs not harmful for heart health” (U.S. News & World Report)

Do these headlines withstand scrutiny? Let’s look at the study’s methodology and results. Like the PURE study, which I previously wrote about here, this was an observational prospective study, meaning the researchers measured certain factors and behaviors (e.g., diet, smoking) and then tracked health outcomes over a period (in this case, nine years on average). Such studies effectively watch for certain outcomes to discover various associations, but never causation. In this particular study, the measured outcomes were cases of cardiovascular disease, including ischemic heart disease, major coronary events, hemorrhagic stroke, and ischemic stroke.

Just over 13 percent of subjects reported consuming eggs regularly at the start of the study; around 9 percent reported either no or very rare consumption. The study reports that over time, the higher egg consumers had an 11 percent lower risk of total cardiovascular disease, 11 percent lower risk of ischaemic heart disease, 14 percent lower risk of major coronary events, 26 percent lower risk of hemorrhagic stroke, 10 percent lower risk of ischemic stroke, and 18 percent lower risk of total cardiovascular death compared to nonconsumers.

These findings sound very impressive for eggs, but there are numerous other considerations. Like the subjects in the PURE study, “nonconsumers” differed from regular consumers in many ways. On average, “nonconsumers” had lower education levels, lower household incomes, and higher rates of smoking and hypertension, and these are only the most obvious of the confounding variables.

Is that convoluted enough for you? Well, hold on, because it gets more complicated.

There is a reason I use quotation marks around nonconsumers: it turns out that the categories of egg consumption reported at baseline (ascertained by a questionnaire administered to participants) do not align with actual consumption (ascertained by follow-up visits). Those who ate the least eggs, classified as “nonconsumers,” actually ate more than two eggs per week. Can this really be classified as nonconsumption? Those who reported eating eggs 1–3 times per month ate nearly 11 eggs each month. Conversely, the highest consumption group, those who reported eating eggs 7 days a week, only ate 5.32 eggs per week. This upper threshold does not, unfortunately, match the reality of high egg consumption in many parts of the world. The average American, much less the highest consumers, ate more eggs than this per week in 2023 (5.4 eggs).^[2]

A study comparing genuinely high egg intake (e.g., 14 eggs per week) with genuine egg abstainers would be much more useful than the narrow scope presented in this study (2 eggs per week versus 5.3 eggs per week).

In all fairness, the journal publication had a far more accurate and less sensationalist title than the media headlines listed above. And if we read past the sensationalist headlines, even some media reports mention the study’s shortcomings. For example, The Daily Mail quoted two independent experts: professor of cardiovascular medicine at the University of Sheffield Tim Chico and senior dietitian at the British Heart Foundation Victoria Taylor. The first said, “It is important to stress that this does not prove that eating eggs protects against these diseases, as there may be other differences between the people eating more eggs that cause these differences;” the second, “It’s possible that the lower risk of cardiovascular disease seen in those who consumed eggs on a daily basis may have been caused by something else in their diet or lifestyle – rather than a specific cause and effect.” Similarly, Newsweek quoted Gavin Sandercock from the University of Essex, UK, who urged caution when reading the results: “If you study enough people you can find a correlation between almost anything. To say that eating eggs is good (or bad) for you based on a study like this would be foolish as diet is much more complicated than picking on one foodstuff like eggs.”

In contrast to the headlines above, outlets that focused more on the study’s flaws had different views:

• “BMJ’s scrambled message on eggs and heart disease: a recipe for rotten news coverage” (HealthNewsReview.org)
• “Eggs Are Good for the Heart… or Not. Here’s why dietary epidemiology research can be rotten.” (MedPage)
• “Scientists link eggs to lower heart disease risk—but are they all they’re cracked up to be?” (Newsweek)

The Bottom Line
This study’s findings and the way they have been reported by media outlets illustrate why it is important to assess evidence in a more wholistic way. The study seemingly suggests that eggs could be beneficial for heart disease, but when we dig deeper we find greater cause for skepticism, not confirmation. Moreover, many other studies have reported harmful effects of eggs, including increased risk of diabetes and advanced and fatal cancers.^[3]–[7] Until we see more convincing evidence to suggest that eggs are healthful for heart disease and other chronic diseases, we should remain cautious about large studies with such obvious flaws as this. Additionally, it would be helpful to see research on the mechanisms behind eggs purported benefits, if any such mechanisms exist.

References

1. Qin C, Lv J, Guo Y on behalf of the China Kadoorie Biobank Collaborative Group, et al. Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults. Heart. 2018;104:1756-1763.
2. Shahbandeh M. Per capita consumption of eggs in the US 2000-2024. Statista.com. February 2, 2024. Online access: https://www.statista.com/statistics/183678/per-capita-consumption-of-eggs-in-the-us-since-2000/
3. Djoussé L, Gaziano JM, Buring JE, Lee IM. Egg consumption and risk of type 2 diabetes in men and women. Diabetes Care. 2009;32(2):295-300. doi:10.2337/dc08-1271
4. Radzevičienė L, Ostrauskas R. Egg consumption and the risk of type 2 diabetes mellitus: a case-control study. Public Health Nutr. 2012;15(8):1437-1441. doi:10.1017/S1368980012000614
5. Wu K, Spiegelman D, Hou T, et al. Associations between unprocessed red and processed meat, poultry, seafood and egg intake and the risk of prostate cancer: A pooled analysis of 15 prospective cohort studies. Int J Cancer. 2016;138(10):2368-2382. doi:10.1002/ijc.29973
6. Zeng ST, Guo L, Liu SK, et al. Egg consumption is associated with increased risk of ovarian cancer: Evidence from a meta-analysis of observational studies. Clin Nutr. 2015;34(4):635-641. doi:10.1016/j.clnu.2014.07.009
7. Si R, Qu K, Jiang Z, Yang X, Gao P. Egg consumption and breast cancer risk: a meta-analysis. Breast Cancer. 2014;21(3):251-261. doi:10.1007/s12282-014-0519-1