Scientist Clarifies Connection Between Eggs, Cholesterol, and Heart Disease

The author of the study spelling bad news for egg lovers explains her results.

In 2019, it’s estimated that each American will eat 279.2 eggs. Most of us will feel good about those choices — especially when our other breakfast options consist of Nutella pancakes or maybe-tainted Honey Smacks. But a new paper released Friday in JAMA points out some long-term consequences to cracking that many shells open.

Leveraging data from six studies on 29,615 adults who were followed over 17.5 years, a team of authors from Northwestern’s Feinberg School of medicine report that eggs or dietary cholesterol consumption are both associated with significantly higher rates of heart disease.

These statistics can seem a bit frightening and have been reported differently by different outlets. Lead study author Norrina Bai Allen, Ph.D., tells Inverse how best to interpret these results.

In her sample, she explains, people who ate 300 mg of cholesterol per day had a 17 percent higher risk of getting heart disease. That 17 percent is reported in the paper as a hazard ratio. She also notes that only 3.21 percent of people in her study actually got heart disease at all, a metric called absolute risk difference. The takeaway is that a very small amount of people in this study developed heart disease, but of those that did, it appears that dietary cholesterol (and that from eggs, in particular) played a role.

“We included the absolute risk because it was very important for people to remember that even though that 17 percent seems like a huge number, it’s actually a very small absolute number of people that have an increased incidence of heart disease,” Allen says.

eggs breakfast
This study indicates that eggs and dietary cholesterol is associated with heart disease, a claim which has been contentious in the past. 

In the paper, she and her co-authors also indicate that eggs are a great enough source of that cholesterol to raise concern. They also report that each additional half of an egg consumed per day is associated with a six percent higher risk of cardiovascular disease. But it’s important to note that when they adjusted for overall cholesterol in someone’s diet, the relationship between eggs and heart disease wasn’t statistically significant.

Some of the other authors of this study, but not Allen, declared funding sources from multiple pharmaceutical companies, including but not limited to Glaxosmith Kline, AstraZeneca and Bayer. These companies all manufacture drugs to treat heart conditions.

“We really looked at whether individuals who ate a higher number of eggs per week experience higher rates of heart disease and mortality,” she explains. “We found that they did in fact have higher risk, but that the risks were actually explained by the cholesterol contained within the eggs. That was the reason we saw this risk of heart disease.”

Contentious Cholesterol

If dietary cholesterol is something to be worried about, her results show that eggs are guilty as charged — a large egg has around 186 mg of cholesterol. But the significance of cholesterol in eggs is contentious: There’s a solid amount of research showing that the amount of cholesterol that’s present in foods, like eggs, isn’t strongly correlated with the dangerous type of cholesterol that can accumulate around the heart.

In 2015, a review released by the American College of Cardiology suggested that this focus on the cholesterol content in foods (including eggs) wasn’t as pressing of a concern as other aspects of diet that contribute to heart disease, like carbohydrate consumption or saturated fats. Though they did call for more research on how dietary cholesterol might impact people with diabetes or existing heart conditions for instance.

Even the 2015-2020 US Dietary Guidelines released by the US Department of Health and Human Services have been recently updated to reflect a more holistic view of diet that looks beyond cholesterol content.

breakfast
Eggs contain a significant amount of cholesterol, but it's not entirely clear if eating cholesterol is really as dangerous as it seems. 

It indicates that “eating patterns that include lower intake of dietary cholesterol are associated with reduced risk of CVD” and go on to emphasize that modifications to the whole diet reduce risk, not simply low levels of dietary cholesterol.

As described earlier, eating patterns consist of multiple, interacting food components and the relationships to health exist for the overall eating pattern, not necessarily to an isolated aspect of the diet.

Allen is aware of these changes regarding cholesterol. In fact, they actually partially inspired her to do this study. She thinks it was worth investigating this relationship in a big data set over nearly two decades to help clarify the relationship, especially in the wake of the updated guidelines.

“There have been long standing recommendations in the dietary guidelines suggested that Americans consume less than 300mg of cholesterol in their diet,” Allen explains. “But in the most recent guidelines this was actually removed given the conflicting evidence and lack of strength of the evidence demonstrating a significant relationship between dietary cholesterol and outcomes.”

“So I think that there was a need for more research to either support or expand the dietary guidelines and provide better understanding.”

In the paper, the authors write that they adjusted for dietary fats or other known dietary risks for heart conditions to really establish whether cholesterol itself is something to be concerned about. Specifically, they accounted for saturated fat, unsaturated fat, trans fat, animal protein, fiber, and sodium. It’s notable that, even after doing so, they were still able to report a relationship between cholesterol, the cholesterol in eggs, and heart disease.

Allen also argues that the length of her study and size of her data set is evidence that we should reconsider the relationship. Clearly, analysis like this something that experts in the field are continuing to pursue, but it might be a bit hasty to turn our backs on eggs right away.

Abstract:

Importance: Cholesterol is a common nutrient in the human diet and eggs are a major source of dietary cholesterol. Whether dietary cholesterol or egg consumption is associated with cardiovascular disease (CVD) and mortality remains controversial.

Objective:To determine the associations of dietary cholesterol or egg consumption with incident CVD and all-cause mortality.

Design, Setting and Participants: Individual participant data were pooled from 6 prospective US cohorts using data collected between March 25, 1985, and August 31, 2016. Self-reported diet data were harmonized using a standardized protocol.

Exposures: Dietary cholesterol(mg/day)or egg consumption(number/day).

Main Outcomes and Measures: Hazardratio(HR) and absolute risk difference(ARD )over the entire follow-up for incident CVD (composite of fatal and nonfatal coronary heart disease, stroke, heart failure, and other CVD deaths) and all-cause mortality, adjusting for demographic, socioeconomic, and behavioral factors.

Results: This analysis included 29,615participants (mean[SD] age,51.6 [13.5]years at baseline) of whom 13 299 (44.9%) were men and 9204 (31.1%) were black. During a median follow-up of 17.5 years (interquartile range, 13.0-21.7; maximum, 31.3), there were 5400 incident CVD events and 6132 all-cause deaths. The associations of dietary cholesterol or egg consumption with incident CVD and all-cause mortality were monotonic (all P values for nonlinear terms, .19-.83). Each additional 300 mg of dietary cholesterol consumed per day was significantly associated with higher risk of incident CVD (adjusted HR, 1.17 [95% CI, 1.09-1.26]; adjusted ARD, 3.24% [95% CI, 1.39%-5.08%]) and all-cause mortality (adjusted HR, 1.18 [95% CI, 1.10-1.26]; adjusted ARD, 4.43% [95% CI, 2.51%-6.36%]). Each additional half an egg consumed per day was significantly associated with higher risk of incident CVD (adjusted HR, 1.06 [95% CI, 1.03-1.10]; adjusted ARD, 1.11% [95% CI, 0.32%-1.89%]) and all-cause mortality (adjusted HR, 1.08 [95% CI, 1.04-1.11]; adjusted ARD, 1.93% [95% CI, 1.10%-2.76%]). The associations between egg consumption and incident CVD (adjusted HR, 0.99 [95% CI, 0.93-1.05]; adjusted ARD, −0.47% [95% CI, −1.83% to 0.88%]) and all-cause mortality (adjusted HR, 1.03 [95% CI, 0.97-1.09]; adjusted ARD, 0.71% [95% CI, −0.85% to 2.28%]) were no longer significant after adjusting for dietary cholesterol consumption.

Results and Relevance: Among US adults, higher consumption of dietary cholesterol or eggs was significantly associated with higher risk of incident CVD and all-cause mortality in a dose-response manner. These results should be considered in the development of dietary guidelines and updates.