Commonly used anti-inflammatory painkillers may increase the risk of heart attacks when taken during a cold or flu, a new study suggests.

The study was based on data on nearly 10,000 patients with an average age of 73 who were hospitalized for a heart attack, also called acute myocardial infarction, in Taiwan from 2005 to 2011. 

Previous studies have shown an increased risk for heart attacks during a respiratory infection, such as cold or influenza, as well as with use of certain anti-inflammatory pain relievers. But the interaction between the infections and class of painkillers wasn't examined.

The non-steroidal anti-inflammatories or NSAIDS include Aspirin, naproxen (Aleve), ibuprofen (Motrin) and arthritis medications such as celecoxib (Celebrex).

Use of NSAIDs during a respiratory infection was associated with a three-fold increased risk of heart attack, Yao-Chun Wen from National Taiwan University Hospital in Taipei and colleagues reported in Thursday's issue of the Journal of Infectious Diseases.

But people suffering from a cold or flu commonly reach for over-the-counter painkillers such as Aspirin or naproxen to relieve fever and aches.

The risk was higher when NSAIDS were given intravenously in the hospital.

Combination of illness, painkiller

"To the best of our knowledge, this study is the first to investigate the joint effects of [acute respiratory infection] and NSAIDs use on the risk of acute myocardial infarction," the study's authors said.

"This approach should raise clinical concern because NSAIDs use during acute respiratory infection episodes is highly common in real-world practice."

Another commonly used pain reliever, acetaminophen, eases pain in a different way than NSAIDs do.

Dr. Jacob Udell, a cardiologist and scientist at Women's College Hospital and Toronto General Hospital, co-wrote a journal commentary on the study.

"Traditionally the cardiovascular guidelines recommend, and I recommend to my patients, that if you've got some pain, if you've got some fever, first try Tylenol in safe doses before having to escalate to anti-inflammatories," Udell said in an interview.

Patients with a lot of pain, such as those with arthritis, may need anti-inflammatories.

"We know now … that that's probably OK. But with regards to treating fever, a pneumonia or a bad infection in the chest, that data's still out. At least in this study, it would suggest that it's potentially harmful to be using those medications in association."

Teasing out cause and effect

One of the strengths of the study, Udell said, is that the researchers used a case-crossover design. The investigators went back and forth in time to see what happened when the subjects didn't have a respiratory tract infection but were taking an anti-inflammatory compared to when they had the infection but were or weren't taking the pain relievers.

"But the problem with any of these studies is ... when you take an anti-inflammatory, why are you taking it? You might be taking it because you have fever. You may be taking it because you have pain. Those things can raise your blood pressure. Those things can raise your pulse rate," Udell said.

It makes it difficult to tease out for sure whether the cause of a heart attack is from anti-inflammatory or the underlying reason you're taking it.

NSAIDs also contain salts that could trigger heart attacks by raising blood pressure and leading patients to retain fluids.

In 2015, the U.S. Food and Drug Administration boosted its warning labels on over-the-counter NSAIDs to highlight elevated risks for heart attack and stroke.

In the latest study, researchers didn't consider the severity of the respiratory tract infection and they couldn't tell whether patients actually took the NSAIDs that were dispensed to them.

Further research is needed to clarify the apparent combined effect on risk and determine how it might be managed.

To that end, Udell has started a randomized clinical trial to test if giving flu shots prevents heart and lung problems and deaths. The results are expected in 2020. 

With files from CBC's Amina Zafar