Egg yolks are just as bad smoking for atherosclerosis, thanks to accumulation of fat and cholesterol, which causes the hardening of arteries by plaques within its walls.

Surveying 1,231 patients, David Spence, professor of neurology at Western University, Canada, found regular consumption of egg yolks is about two-thirds as bad as smoking regarding increased build-up of plaque, a risk factor for stroke and heart attack.

The study looked at data from men and women, with a mean age of 61.5 years, attending vascular prevention clinics at London Health Sciences Centre’s University Hospital, the journal Atherosclerosis reports.

Ultrasound was used to establish a measurement of total plaque area and questionnaires were filled out regarding their lifestyle and medications including pack-years of smoking (number of packs per day of cigarettes times the number of years), and the number of egg yolks consumed per week times the number of years consumed (egg yolk-years).

The study also found those eating three or more yolks a week had significantly more plaque area than those who ate two or fewer yolks per week, according to a Western statement.

“The mantra ‘eggs can be part of a healthy diet for healthy people’ has confused the issue. It has been known for a long time that a high cholesterol intake increases the risk of cardiovascular events, and egg yolks have very high cholesterol content. In diabetics, an egg a day increases coronary risk by two to five-folds,” says Spence.