It's genetics and not tobacco that plays the major part in causing a heart attack in cigarette smokers, says a new study.
According to the study, a common defect in a gene that controls cholesterol metabolism increases smokers' risk of an early heart attack.
The study was led by Ilan Goldenberg, M.D., Research Associate Professor in the Cardiology Unit of the University of Rochester Medical Center's Department of Medicine and the Heart Institute and Neufeld Research Institute at Sheba Medical Center in Tel Hashomer.
It was shown through the results that smokers without the defect normally do not have heart attacks earlier than their non-smoking peers.
However, the link between smoking and heart disease was recognized long back but the reasons for that link were unclear.
Recent studies suggested that smoking interferes with cholesterol metabolism that decreases smokers' levels of high-density lipoprotein, the good cholesterol that protects against heart-attack risk.
About 55 to 60pct of smokers are prone to the added risk of a defective gene that also lowers levels of the protective high-density lipoprotein.
Thus, the combination of smoking plus a defective gene significantly heightens the risk of heart attacks in these patients.
These researchers were the first to evaluate both smoking history and the genetic trait in heart-attack patients.
It was found that smokers with the genetic defect experienced their first heart attack eight to nine years earlier than non-smokers.
However, smokers with a healthy version of the gene experienced their first heart attack just three years earlier than non-smokers, which is a difference the researchers considered non-significant.
"Since the frequency of this 'bad' gene in the general population is about 60 percent, many people who smoke have a high risk of experiencing a heart attack at a young age," Goldenberg said.
He added: "This finding should increase awareness for smoking cessation."
The study is published in Annals of Noninvasive Electrocardiology.