Can a flu shot reduce your risk of stroke?
Studies show that infections, particularly respiratory infections, are associated with stroke and heart attack. One proposed reason for this is that infections may disrupt plaques in the arteries, causing blood clots that block blood flow to the brain (a stroke) or heart (a heart attack). Getting a flu shot helps prevent the flu—a viral respiratory infection—and subsequent bacterial respiratory infections. With this in mind, researchers in Paris, France examined whether flu vaccination could reduce a person's risk of stroke. According to their study published in the recent issue of Stroke: Journal of the American Heart Association , people over age 60 who receive flu shots may be less likely to have a stroke.
About the study
This study included 90 men and women aged 60 or older who were admitted to a Paris hospital for stroke (cases) and 180 free-living Parisians aged 60 or older (controls). The 90 cases were admitted to the hospital and enrolled in the study either between December 1998 and March 1999 or January and March 2000. The 180 controls were identified from electoral rolls and enrolled in the study as matched controls, meaning that their age, sex, and district of residency in Paris matched that of a case subject. For each case subject, there were two matched controls.
Case subjects were examined and interviewed during their hospital stays by a neurologist. The same neurologists interviewed control subjects by telephone. The neurologist interviewers asked both cases and controls about factors related to stroke risk, such as hypertension, diabetes, smoking, cholesterol levels, history of heart attack and heart procedures, stroke, transient ischemic attack, and type of employment (blue or white collar jobs). Subjects were also asked whether they had received a flu vaccination during the most recent vaccination campaign and if they had been vaccinated every year for the past five years.
The researchers compared the number of cases who had been vaccinated with the number of controls who had been vaccinated.
Fifty-nine percent of controls had been vaccinated in the most recent vaccination campaign compared with only 46% of stroke patients, and 56% of controls had been vaccinated annually for the previous five years compared with only 41% of stroke patients. When the researchers factored in participants' risk factors for stroke, flu vaccination reduced the risk of stroke by 55% in people vaccinated during the year of the study and 63% in people vaccinated annually for the previous five years.
Of interest, participants over age 75 were less likely to benefit from flu vaccination than their 60- to 75-year-old counterparts. Further study is needed to examine this finding.
There are limitations to this study, however. First, people who make sure to get flu shots may also have other healthful habits that could explain why vaccinated people in this study were less likely to have a stroke. For example, they may eat healthier diets, refrain from heavy drinking, and exercise more regularly.
In addition, the findings of this study do not identify the mechanism by which flu shots might reduce the risk of stroke. The researchers propose that infections may lead to stroke by disrupting atherosclerotic plaques in the arteries and causing blood clots. They reason that a flu shot might reduce the number of infections in a given year, thereby reducing the probability that an infection will lead to a stroke. Further research is needed to investigate this proposed mechanism.
How does this affect you?
Although this is the first study to examine the influence of flu vaccination on stroke risk, these results add to mounting evidence that infection may be an important risk factor for stroke and heart attack. The results also suggest that preventing influenza infection and subsequent bacterial infections may reduce your risk of having a stroke. The authors note that further research is needed to fully understand the relationship between flu vaccination and stroke.
Should you get a flu shot to prevent stroke if you are over age 60? Getting a flu shot each fall definitely reduces your chances of getting the flu each winter, but it's still questionable whether it reduces your chances of having a stroke. Regardless of the connection between flu shots and stroke, however, flu shots are recommended for adults aged 65 and older, because the flu can be life threatening in older people.
If you want to reduce your risk of stroke, you'll need to do more than have a flu shot. The National Stroke Association recommends that you:
- Keep your blood pressure and cholesterol levels in a healthy range either with a healthy diet or medications prescribed by your doctor
- Do not smoke
- Drink only moderate amounts of alcohol (one drink per day for women and two drinks per day for men)
- Maintain a healthy weight
- Eat a balanced diet that is low in fat and cholesterol and includes fruits and vegetables, lean meats such as chicken and fish, low-fat dairy products, whole grains, and a limited number of eggs
Lavallée P, et al. Association between influenza vaccination and reduced risk of brain infarction.
Stroke . February 2002;33:513-518.
Last reviewed Feb 1, 2002 by ]]>Richard Glickman-Simon, MD]]>
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