A stroke can change a person’s life in many ways. Some people recover well and regain most of their abilities, but others later develop problems with memory, concentration, and thinking. Doctors have long tried to understand why some stroke survivors experience these cognitive problems while others do not.
A new study from researchers at The University of Manchester suggests that the answer may lie in a hidden process inside the body—ongoing inflammation after the stroke.
A stroke happens when blood flow to part of the brain is blocked or reduced. Without enough oxygen and nutrients, brain cells begin to die.
The most common type is called an ischemic stroke, which occurs when a blood clot blocks an artery supplying blood to the brain. Strokes are a major cause of disability around the world. Even after the initial emergency is over, many patients face long-term health challenges.
One of the most concerning long-term effects is cognitive decline. This means problems with memory, attention, decision making, and other thinking skills. These difficulties can appear months or even years after the stroke. In some cases, they can become severe enough to interfere with daily life.
Scientists have suspected that inflammation may play an important role in these long-term brain problems. Inflammation is the body’s natural response to injury. When tissues are damaged, the immune system releases chemicals that help protect and repair the body. However, if inflammation continues for too long, it may begin to harm healthy cells.
To explore this idea, researchers from The University of Manchester studied a protein linked to inflammation called interleukin‑6, often shortened to IL‑6. This protein is produced by the immune system and can increase when the body is responding to injury or infection.
The research was part of a large international project known as the Stroke IMPaCT study, which stands for Stroke—Immune Mediated Pathways and Cognitive Trajectory. This project brings together scientists from Europe and North America who are working to understand how immune responses after stroke affect brain health over time.
In this study, the research team followed patients who had been treated for ischemic stroke at Salford Royal Hospital, which is part of the Northern Care Alliance NHS Foundation Trust in the United Kingdom.
The scientists measured levels of IL‑6 in the patients’ blood shortly after the stroke. They then measured the levels again several months later, between six and nine months after the stroke, and once more between eighteen and twenty‑one months later.
At the same time, the patients completed detailed tests designed to measure memory, thinking ability, and other cognitive skills. By comparing inflammation levels with the results of these tests, the researchers hoped to see whether changes in IL‑6 were linked to later problems with thinking.
The results revealed an important pattern. In most patients, IL‑6 levels rose soon after the stroke. This was expected, since the body was responding to the injury. Over time, the levels gradually returned to normal. For many people, inflammation appeared to settle down within six to nine months.
However, this was not the case for everyone. Some patients continued to show high levels of IL‑6 long after the stroke, and in some cases the levels even increased again later. These individuals were far more likely to develop cognitive problems.
According to the researchers, patients whose IL‑6 levels remained high were about eight times more likely to experience difficulties with memory and thinking.
The study also found an interesting difference between smokers and non‑smokers. People who smoked showed a different pattern of inflammation after their stroke. Their IL‑6 levels suggested that inflammation lasted longer in their bodies. This prolonged immune response was more strongly linked to problems with memory and thinking.
Natasha Carmichael, the lead author of the study and an MBPhD researcher at The University of Manchester, explained that inflammation after a stroke is not always a short‑term event.
In some people it continues quietly for months or even years. By tracking IL‑6 levels over time, doctors may one day be able to identify patients who are at greater risk of developing cognitive problems.
Professor Craig Smith, Professor of Stroke Medicine at The University of Manchester and Consultant at Salford Royal Hospital, said the research suggests that the key factor may not be the initial burst of inflammation after the stroke.
Instead, what matters most is whether the body’s immune response settles down properly during recovery. Smoking may interfere with this recovery process, leaving patients more vulnerable to long‑term brain problems.
Professor Stuart Allan added that when the immune system does not return to normal after a stroke, patients appear to be more likely to experience cognitive decline. If future studies confirm that IL‑6 plays a direct role in causing these problems, scientists may eventually develop medicines that block or control this protein in order to protect the brain.
Co‑lead author Harry Deijnen also emphasized that more research is needed before these findings can be turned into new treatments. However, the study opens the door to a new way of thinking about stroke recovery.
Instead of focusing only on the immediate damage caused by the stroke, doctors may also need to pay attention to how the immune system behaves during the months and years that follow.
If you care about stroke, please read studies about how to eat to prevent stroke, and diets high in flavonoids could help reduce stroke risk.
For more health information, please see recent studies about how Mediterranean diet could protect your brain health, and wild blueberries can benefit your heart and brain.
The study was published in the scientific journal Alzheimer’s & Dementia.
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