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"People at risk of vascular disease should not eat egg yolks," contends study lead author Dr. David Spence, professor of neurology at Western University in London, Ontario, Canada.
The cholesterol found in an egg's yellow center can even clog the carotid artery leading to the brain, upping risks for stroke, he pointed out.
"Carotid plaque goes up steeply with age, so the only people who can eat egg yolks with impunity are those who know they will die young from some cause other than vascular disease," Spence said.
The report was published online this month in Atherosclerosis.
For the study, Spence's team collected data on more than 1,200 men and women who were taking part in an initiative aimed at curbing heart disease.
The researchers used ultrasound to first determine the amount of plaque in each patient's arteries. They then asked patients about smoking, their frequency of eating eggs, other lifestyle factors and any medicines they were taking.
Although artery plaque levels rose with age, both smoking and eating egg yolks sped up this plaque formation within vessels, the researchers found. Regular consumption of egg yolks sped up plaque deposits in arteries at a rate that was about two-thirds the rate seen with smoking, Spence said.
People who ate three or more yolks a week had significantly increased plaque compared with people who ate two or fewer yolks a week, the team found. That makes sense, Spence said, since just "one egg yolk contains more than the recommended daily intake of cholesterol."
An expert not connected to the study agreed. According to Samantha Heller, clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn., "it is known that the amount of cholesterol in many egg yolks is more than the recommended 200 milligrams per day for people with risk factors for cardiovascular disease."
The study authors noted that the effect of egg yolks on plaque was independent of the person's sex, cholesterol levels, blood pressure, smoking, weight and diabetes.
In a statement, the American Egg Board said that the findings come from "an observational study that can only suggest potential relationships,not determine actual cause-and-effect conclusions."
The Egg Board also noted in the statement that "study subjects with higher egg intakes tended to also be heavy smokers, and only a small percentage of the population consumed more than five eggs per week, meaning that the conclusions were based on a small number of subjects."
Dr. Gregg Fonarow, a spokesman for the American Heart Association and professor of cardiology at the University of California, Los Angeles, said the evidence for and against egg yolk consumption has see-sawed for decades.
"Whether dietary egg consumption is associated with an increased risk of cardiovascular disease has been controversial and previous studies have been inconsistent," Fonarow said. He said the jury remains out on the issue, pending further study.
Right now, Fonarow said, "the American Heart Association recommends for maintaining heart and brain health to eat a variety of nutritious food from all the food groups, with emphasis on vegetables, fruits, whole-grain products and fat-free or low-fat dairy products as well as eating fish at least twice a week."
Heller stressed, though, that cholesterol lurks in many foods, including meat and cheese, and foods that are made with eggs, such as baked goods.
She wondered if the study might be targeting egg yolks and missing some of these other sources of cholesterol.
"Most animal foods also contain saturated fat, which increases internal inflammation and serum [blood] cholesterol," Heller noted. "The study does not take into account other foods that contain cholesterol, saturated fat or egg yolks. Could it be that people who eat a lot of eggs also combine them with other less healthy foods such as cheese or sausage?"
The Egg Board agreed. "The study did not control for exercise habits, waist circumference, intake of saturated fat, alcohol or foods commonly eaten with eggs like high-fat meats and other high-fat side dishes," it said in the statement.
On the other hand, egg whites remain an excellent source of protein and a great alternative to the whole egg, Heller said.
"Though some people complain that egg whites do not taste as good as the whole egg, adding vegetables like spinach, onions or mushrooms, herbs and a pinch of turmeric to make the egg whites yellow -- the visual seems to make a difference here -- can create a delicious and healthy meal," Heller said.
Research suggests a more plant-based diet -- which means eating fewer eggs, less cheese, red and processed meats, and more vegetables, beans, nuts and fruits -- may improve risk factors for cardiovascular disease such as high cholesterol, blood pressure and triglycerides, she added.
Copyright © 2012 HealthDay. All rights reserved.
SOURCES: David Spence, M.D., professor of neurology, Western University, London, Ontario, Canada; Gregg Fonarow, M.D., spokesman, American Heart Association, and professor, cardiology, University of California, Los Angeles; Samantha Heller, M.S., R.D., exercise physiologist, clinical nutrition coordinator, Center for Cancer Care, Griffin Hospital, Derby, Conn.; Aug. 14, 2012, statement, Egg Nutrition Center/American Egg Board; Aug. 9, 2012, Atherosclerosis, online