Unscrambling the Science Behind Eggs and Heart Health

Sworn off eggs because you heard they were bad for your heart? Turns out, eggs have a complicated history with heart health. Because cardiovascular disease (CVD) is the leading cause of death worldwide, and diet plays an important role in the development of CVD, there is a good deal of research interest in examining the relationship between diet and CVD. As such, a new observational study examined the relationship between egg consumption and CVD, delivering a much-needed sunny side to the science.

Key Points of the Study

Researchers used data from an ongoing observational study of more than half a million adults aged 30 to 79 from 10 different locations in China. They narrowed their focus to people who had not been previously diagnosed with cancer, diabetes or CVD, resulting in a sample size of just over 461,000 people. Participants were asked how often they ate eggs, along with other questions about their diet and health history, and were stratified by level of egg intake. Then the highest and lowest levels of intake were compared: 13 percent of participants reported eating eggs daily (amounting to about ¾ of an egg per day), while 9 percent said they never or rarely consumed eggs (about ⅓ of an egg per day).

After nearly nine years of follow-up, 83,977 people had been diagnosed with CVD, 9,985 of whom had died. There were 5,103 "major coronary events," such as stroke or heart attack. Results showed that daily egg consumption was associated with an 11 percent reduction in risk of developing CVD as compared to those who never or rarely consumed eggs, as well as an 18 percent lower risk of death from CVD. Daily egg consumers also had a 26 percent lower risk of hemorrhagic stroke and a 12 percent reduced risk of ischemic heart disease.

With these findings, the study concluded that "a moderate level of egg consumption (up to <1 egg/day) was significantly associated with lower risk of CVD”.

Putting the Findings into Context

There are a number of strengths to this study. Its sample size is among the largest of its kind, which can be more reflective of the Chinese population, while limiting the influence of outliers. Researchers adjusted for many variables in their analyses, which can reduce confounding, a phenomenon that can occur when other variables that might affect the outcome aren’t accounted for.

For example, having a higher body weight and being a smoker increase the risk of CVD, so it’s important to consider these variables alongside food choices. By excluding participants who had CVD, diabetes or cancer at the beginning of the study, authors minimized reverse causality, which can happen if a person changes the way they eat as a result of being diagnosed with a certain health condition.

However, because this was an observational study, it can provide only a correlation between egg intake and CVD. It does not prove that eating eggs protects against CVD. It’s important to note that eating patterns and health histories of this study population are likely different than the average American. Egg intake isn’t especially high in China, so the study couldn’t provide information on the health effects of eating more than one egg a day. Participants were typically a healthy weight, and most of them didn't have high blood pressure or a family history of heart disease.

In the U.S., most adults are overweight or obese and eat a Western diet higher in red meat, dairy and refined sugar, and lower in fiber and healthy fats. Therefore, the connection between eggs and heart disease might look quite different if studied in Americans.

This new research lends additional support to a growing body of literature indicating that eating eggs does not increase risk for CVD. A 2017 systematic review showed no changes in major cardiovascular risk factors, including higher rates of blood sugar, inflammation and cholesterol, when participants consumed between six and 12 eggs per week. The lead author of that systematic review has stated to CNN that this new study "delivers a similar message" that "egg consumption does not increase the risk of developing a cardiovascular disease," and “consuming eggs as part of a healthy diet does not increase the risk of cardiovascular disease.”

Eggs, Nutrition and the Dietary Guidelines

Eggs are rich in protein, vitamins and choline, an important nutrient for cognitive function and infant growth and development. Some brands of eggs also may be enriched with vitamin D and omega-3 fatty acids.

And yet, despite their nutritious benefits, eggs have endured a long and complicated relationship with health guidelines and the media. Decades ago they were under fire over concerns around their dietary cholesterol content. Elevated blood cholesterol is associated with increased risk for heart disease, so foods high in cholesterol were assumed to be bad for cardiovascular health.

But since then, research has determined that for most people, dietary cholesterol intake has little impact on blood cholesterol levels. Studies have also shown that eggs may actually help raise high-density lipoprotein (HDL) cholesterol, also known as the “good” cholesterol that helps remove other harmful forms of cholesterol from the bloodstream.

In 2015, daily limits on dietary cholesterol intake were removed from the Dietary Guidelines for Americans, and the current Dietary Guidelines for Americans recommend including eggs in the diet along with other protein foods. Of course, it’s important to consider the foods you’re eating alongside your eggs. No one food is eaten in isolation, and following an overall healthy eating pattern is a key factor in reducing risk for diet-related diseases like CVD.

For optimal heart health, the American Heart Association recommends the Dietary Approaches to Stop Hypertension (DASH) diet or a Mediterranean-style diet. Both diets emphasize unsaturated vegetable oils, nuts, fruits, vegetables, low-fat dairy products, whole grains, fish and poultry, and both limit red meat, as well as foods and drinks high in added sugars and salt.

This blog includes contributions by Megan Meyer, PhD.

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