Stroke significantly increases the risk of dementia

In the largest study of its kind, researchers conclude that stroke doubles the risk that an individual will eventually develop dementia.

In the United States, somebody has a stroke every 40 seconds. Stroke kills an estimated 140,000 people each year.

Stroke is responsible for 1 in 20 deaths in the U.S.

Dementia, a seemingly unrelated neurological condition, affects about 8.8 percent of all U.S. adults over the age of 65; some 4 to 5 million older adults, in total.

Studies have, in the past, demonstrated a link between stroke and an increased risk of developing dementia. So far, however, it has not been possible to assess exactly how much risk increases.

As the U.S. population's average age rises and stroke survival becomes more common, knowing the size of the risk is of growing importance. The more we understand the factors that influence dementia, the more chance we have of finding ways to reduce risk.

Stroke and dementia risk

Recently, researchers analyzed a host of previous studies to draw more solid conclusions about the potential links between stroke and dementia.

Scientists from the University of Exeter Medical School in the United Kingdom have now published their findings in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

Led by Dr. Ilianna Lourida, the team took information from 48 studies, which included data from around 3.2 million participants. This, the largest meta-analysis of its kind, generated clear links between the two conditions.

"We found that a history of stroke increases dementia risk by around 70 percent, and recent strokes more than doubled the risk."

Dr. Ilianna Lourida

The results remained significant even after controlling for known dementia risk factors, such as high blood pressure, cardiovascular disease, and diabetes.

Dr. Lourida explains why their findings matter: "Given how common both stroke and dementia are, this strong link is an important finding. Improvements in stroke prevention and post-stroke care may, therefore, play a key role in dementia prevention."

Future research and conclusions

The authors identified differences in risk between individual studies; they believe that this might be due to the region of the brain affected by the stroke and how much damage occurred in the tissue.

The team also thinks that increased dementia risk following stroke might be more pronounced in men. However, this will need further research to clarify.

The authors hope that scientists will continue this line of investigation and identify other factors that might be involved; for instance, ethnicity and education are known to play a part in dementia risk, so understanding how stroke might modify risk in different populations would be useful.

Study co-author Dr. David Llewellyn concludes, "Around one third of dementia cases are thought to be potentially preventable, though this estimate does not take into account the risk associated with stroke."

"Our findings indicate that this figure could be even higher, and reinforce the importance of protecting the blood supply to the brain when attempting to reduce the global burden of dementia."

With stroke and dementia so prevalent in the U.S., understanding the relationship between the two is more important than ever. There is still much to learn, but the new study adds to our knowledge substantially.