One Egg a Day? No Link to Risk of CVD, Mega-Meta-analysis Says

The humble egg, much maligned for the nearly 200 mg of cholesterol found mostly in its yolk, has gained fresh support from a massive new meta-analysis suggesting that eating one egg per day is not going to spike anybody’s risk of cardiovascular disease.

The new data appear in the BMJ this week; along with the updated meta-analysis, the paper includes a systemic review and a large, prospective analysis of several US cohort studies. In the latter, which included more than 215,000 men and women in the Nurses’ Health Study (NHS), NHS II, and Health Professionals Follow-up Study (HPFS) tracked for up to 30 years, eating an egg a day was not associated with an increased risk of incident CVD after adjusting for lifestyle and dietary factors.

Similarly, in the updated meta-analysis of prospective cohort studies that involved 1,720,108 participants, moderate egg consumption was not associated with an increased risk of CVD, coronary heart disease, or stroke.

Lead investigator Jean-Philippe Drouin-Chartier, PhD (Harvard TH Chan School of Public Health, Boston, MA), boiled all of the data down for TCTMD in a single, simple conclusion: “The main message is that eating up to one egg per day is not associated with an increased risk of cardiovascular disease.”

Despite the relatively straightforward message, the findings are yet another thrust in the battle over just where eggs should fit in our diet, one that has been ongoing for many years, said Drouin-Chartier. Back in 1999, Frank Hu, MD, PhD (Harvard TH Chan School of Public Health/Brigham and Women’s Hospital), published the first large-scale epidemiological study using data from the NHS and HPFS showing that moderate egg consumption was not associated with an increased risk of CVD. Prospective cohort studies in recent years have shown mixed results, with some showing an association between eating eggs and CVD, some showing no risk whatsoever, and others suggesting that eating eggs might even be protective.

Last year, there was a large analysis published in the Journal of the American Medical Association by researchers analyzing six cohort studies from the Lifetime Risk Pooling Project. That study, which included nearly 30,000 participants, showed that each additional 300 mg of dietary cholesterol consumed and each additional half an egg eaten per day was associated with an increased risk of incident CVD and all-cause mortality.

“With this ongoing debate, it motivated us to first update Frank Hu’s analysis by including 10 more years of follow-up, which included more than 10 times the number of [CVD] cases in the analysis, and also by adding the younger cohort from the Nurses’ Health Study II,” said Drouin-Chartier.

Egg Consumption Quite Low

In the prospective study, the cohort analyses included 83,349 women from NHS, 90,214 women from NHS II, and 42,055 men from HPFS free of CVD, type 2 diabetes, and cancer at baseline. Over 32 years of follow-up, 14,806 subjects developed CVD. Egg consumption, assessed using food frequency questionnaires, was low in the study. At baseline, mean intake was 0.42 eggs per day in the NHS, 0.18 eggs in NHS II, and 0.34 eggs in HPFS. Consumption decreased between 1980 and 1994 but then remained stable. In 1998-1999, just 1.24% of subjects ate at least one full egg per day and only 0.20% ate at least two eggs daily.

Compared with individuals who ate less than one egg per month, those who ate at least one egg per day did not have an increased risk of incident CVD (HR 0.93; 95% CI 0.82-1.05). Similarly, there was no increased risk of coronary heart disease (HR 0.90; 95% CI 0.77-1.05) or stroke (HR 0.99; 95% CI 0.81-1.22). There was also no increased risk of CVD among those who ate at least two eggs per day.

In the updated meta-analysis and systematic review, which included 28 studies, the pooled relative risk for CVD among men and women who ate one egg daily was not statistically significant (RR 0.98; 95% CI 0.93-1.03). Additionally, those in the highest category of egg consumption were not at an increased risk of incident CVD, coronary heart disease, or stroke compared with those in the lowest category. Results were similar in patients with type 2 diabetes and in US and European cohorts. In Asian cohorts, there was a hint that egg consumption was associated with a lower risk of CVD (RR 0.92; 95% CI 0.85-0.99).       

Despite their analysis, Drouin-Chartier suspects this isn’t the final word on eggs and CVD. Still, their systematic review and meta-analysis provided a comprehensive look at studies published to date, and any future studies will need to be placed within the context of their large analysis.

One of the reasons they updated the meta-analysis was to help eliminate some of the uncertainties surrounding eggs, Drouin-Chartier told TCTMD. “If we limited ourselves to the cohort analysis of the three Harvard cohorts, it would have been just another publication saying that eggs are not associated with cardiovascular disease and creating more confusion.”

In 2015, the US dietary guidelines dropped the previous recommendation to limit dietary intake of cholesterol to 300 mg per day for the prevention of CVD given the weak association between dietary and blood cholesterol. “It wasn’t considered a nutrient of concern for overconsumption,” said Drouin-Chartier.

‘Shouldn’t Put All Our Eggs in This Observational Basket’

In an editorial, Andrew Odegaard, PhD (University of California, Irvine), states the media attention and reaction to these latest findings “will either frame it as the latest volley in an epic tennis match between two camps, or condemn it due to the study design.”

While the results are convincingly null save for a few subgroups, Odegaard argues that “we shouldn’t put all our eggs in this observational basket” for formal guidance given the challenges of nutritional research. The results should be included with evidence from different study designs and populations to provide the best evidence about eggs, or diet in general, and disease.

“So we must filter out the noise with an evidence-informed take-home message,” writes Odegaard. “If frequent egg consumption is occurring in the context of an overall dietary pattern known to be cardioprotective, or eggs are being consumed for essential nutritional needs, then it is probably nothing to worry about. If frequent egg consumption is occurring in the context of a typical Western dietary pattern (high levels of refined grains, added sugars, red and processed meats, and ultraprocessed foods), the best evidence for cardioprotection supports shifting one’s overall dietary pattern to a Dietary Approaches to Stop Hypertension (DASH) or Mediterranean diet.”

To TCTMD, Drouin-Chartier said he also believes that egg consumption should be part of a balanced diet that involves plants, whole grains, low-fat dairy, and fruit. “One egg per day in a healthy diet is totally fine,” he said.