People who are ill with respiratory or urinary tract infections face a higher risk of heart attack or stroke while they are sick, researchers said on Wednesday.
But the researchers -- who examined more than 5 million patient records in England and Wales to test a theory that the risk of heart attack and stroke rises when the lining of blood vessels becomes inflamed -- found that vaccination against the flu, tetanus or pneumonia, which also causes inflammation, does not increase the risk.
In fact, flu shots seemed to reduce the danger, but only in the short term.
The team, led by Liam Smeeth of the London School of Hygiene and Tropical Medicine, discovered that the real risk came when the inflammation was caused by illness.
“This study provides support for the concept that inflammation is an important factor is atherosclerotic disease and also provides reassurance that vaccination does not increase the risk of vascular events,” according to the editors of the New England Journal of Medicine, where the study appears.
During the first three days of a respiratory tract infection, the risk of a heart attack increased by 395 percent and the likelihood of a stroke was 219 percent higher than normal.
It wasn’t just the strain on the lungs and throat that increased the risk. People with urinary tract infections had a higher risk as well -- 66 percent higher for a heart attack and 172 percent higher for a stroke during the first three days of the infection.
The risk declined gradually over time, but it was still elevated for up to 28 days.
If nothing else, the findings show that the risk of having a heart attack or stroke fluctuates, suggesting that short-term infections may trigger such problems, the researchers said.
In contrast, a flu shot cut the risk of heart attack by 25 percent and stroke by 23 percent during the first three days after the vaccination.
However, the Smeeth team said, “The small protective effect seen after vaccination may have been due to the administration of vaccination when people were in periods of relatively good health.”