New Canadian research shows just how dangerous the flu can be, revealing that the illness raises the chances of a heart attack by six times during the first week.
The study published in the New England Journal of Medicine is the first to quantify the risk between heart attacks and laboratory-confirmed influenza.
The researchers led by Dr. Jeff Kwong at the Institute for Clinical Evaluative Sciences (ICES) used data on patients from Ontario who were diagnosed with flu within a year of having a heart attack.
Dr. Kwong told CTV News "We were shocked by how strong the association was. Six-fold is very high… To have it at six is a strong association. It’s comparable to the association between lung cancer and smoking."
The risk of heart attacks was found to be somewhat higher for those over the age of 65 and for patients infected with an influenza B strain of the flu, rather than influenza A.
The study also found the risk of a heart attack was elevated to a lesser extent after infection with other common respiratory viruses.
Dr. Kwong told CTV News there are several ways that a respiratory infection like the flu can lead to a heart attack.
The infections can lower blood pressure, lowering the amount of oxygen in the blood forcing the heart to compensate by beater faster. That can of strain can lead ot a heart attack in those with early heart disease.
Viral infections cause inflammation, which promotes blood clots forming in the blood vessels that serve the heart, again leading to a heart attack.
The authors note that it’s not clear whether their findings apply only to those who develop flu infections, serious enough to result in laboratory testing, since those were the only patients they studied.
"Since most patients with milder symptoms do not undergo testing for respiratory viruses, these findings may not be generalizable to milder infections," they write.
Dr. Kwong tells CTV News the findings are a good reminder of why it is so important for everyone to get a flu shot, particularly those who have early heart disease.
With files from CTV News