A recent study has linked higher consumption of eggs or dietary cholesterol to a higher risk of cardiovascular disease and premature death. The finding is likely to rekindle the debate on eggs and heart health.
For example, the new study seems to contradict the decision in the United States to omit specific limits on daily intakes of dietary cholesterol and eggs from official advice on healthful eating.
Researchers from Northwestern University Feinberg School of Medicine in Chicago, IL, and other institutions pooled and analyzed data from six U.S. cohort studies covering a total of 29,615 people. Of these, 45 percent were male and 31 percent were black.
They compared eating patterns at baseline, when the average participant age was 52 years, with cardiovascular diseases and deaths that occurred during a follow-up that lasted up to 31 years and whose midpoint was 17 years.
The team describes the findings in a JAMA paper.
Co-corresponding study author Norrina B. Allen Ph.D., an associate professor of preventive medicine at Northwestern, says that the "take-home message" of the study "is really about cholesterol, which happens to be high in eggs and specifically yolks."
"People who consume less cholesterol have a lower risk of heart disease," she adds.
Guidelines do not limit cholesterol or eggs
According to the Centers for Disease Control and Prevention (CDC), heart disease is the "leading cause of death" in the U.S.
For decades there has been a debate about whether consumption of eggs or dietary cholesterol raises the risk of heart disease and early death.
The official recommendation in the U.S. before 2015 was that people should limit their daily egg consumption to no more than 300 milligrams (mg), which is less than two large eggs.
The more recent Dietary Guidelines for Americans 2015–2020, however, no longer provide limits on dietary cholesterol and egg intake. They include weekly intake of eggs as part of a healthful diet.
"Adequate evidence," they claim, "is not available for a quantitative limit for dietary cholesterol specific to the Dietary Guidelines."
The revised guidelines do, however, retain the message that the choice to drop specific limits does "not suggest that dietary cholesterol is no longer important to consider when building health[ful] eating patterns."
Only foods of animal origin — including dairy products, eggs, shellfish, poultry, and meat — contain dietary cholesterol.
Of the foods most typical of the U.S. diet, eggs contain the most cholesterol. There are around 186 mg of cholesterol in the yolk of a large egg.
The average U.S. adult consumes about 300 mg of dietary cholesterol per day and about three or four eggs per week.
Higher risk of heart disease and death
Dr. Allen believes that the problem with studies that have found no links between egg consumption and higher risk of cardiovascular disease is that they used less diverse samples and shorter follow-ups, and that they were less able to adjust for other items in the diet.
"Our study," she notes, "showed if two people had [the] exact same diet and the only difference in diet was eggs, then you could directly measure the effect of the egg consumption on heart disease."
The dietary data for the new study came either from completion of questionnaires or interviews that took place during a single visit. These yielded details of what each person had eaten either in the previous year or month.
Around 5,400 cardiovascular events and 6,132 deaths from all causes occurred over the follow-up period. Examples of cardiovascular events include diagnoses of heart disease, stroke, and heart failure.
The scientists found that for "each additional" intake of 300 mg of dietary cholesterol per day, there was a significant 17 percent higher risk of cardiovascular disease and 18 percent higher risk of death from any cause.
The team also calculated the "absolute risk differences" for these results. These were 3.24 percent and 4.43 percent, respectively.
In other words, for every 1,000 participants in their study, there were 32 additional diagnoses of cardiovascular disease and 44 deaths for every extra 300 mg of cholesterol consumed per day.
The analysis also showed that for each additional half egg eaten per day, there was a 6 percent higher risk of cardiovascular disease and an 8 percent higher risk of all-cause death.
The overall quality of people's diet, the type and amount of fat that they ate, and the amount of exercise that they undertook appeared to have no effect on these links.
"These results," explain the study authors, "should be considered in the development of dietary guidelines and updates."
Single snapshot of diet pattern
Among the study's strengths are the fact that it used a large and diverse sample of people from the U.S., and that there was a long follow-up period.
However, one limitation worth noting is that it only used a single snapshot of egg and cholesterol consumption, and that was at the beginning of the follow-up. People can change their eating habits, and 17–31 years offers plenty of opportunity to do so.
Commenting on the findings, Tom Sanders — who is a professor of nutrition and dietetics at King's College London in the United Kingdom — points out that because the study is prospective, it cannot establish cause and effect; it can only suggest links.
"However," he adds, "the take-home message supported by the accompanying editorial would support the view that a typical [U.S.] diet, which contains lots of meat and plenty of eggs, is associated with poor cardiovascular health and that the [country's] dietary guidelines should reinstate its recommendation that cholesterol intake should not exceed 300 mg per day."
"As part of a healthy diet, people need to consume lower amounts of cholesterol."
Norrina B. Allen Ph.D.