Association between lower cerebral blood flow and cognitive decline Research shows deterioration of cerebral blood flow in ten years in memory complaints

A study of Radboud university medical center among 28 older adults shows that the cerebral blood flow of people who develop early memory problems decreases faster than that of people without memory problems. The older adults were examined twice within an interval of ten years, which is often difficult to implement in scientific research. The results were recently published in The Journal of Cerebral Blood Flow & Metabolism and Geroscience. 

The risk of dementia increases with aging. Eventually, about 20% of people over the age of 80 will develop some form of dementia, such as vascular dementia or Alzheimer's. No single cause of the disease has yet been found. Much research focuses on the question of how dementia develops and whether it can be prevented.  

Ultrasound

One of these studies was carried out by Ralf Weijs, PhD candidate at Radboud university medical center. He invited a group of older people to repeat measurements that they had undergone ten years ago. This made it possible to investigate what changes had occurred in ten years. 28 of the original 48 participants re-entered. Their physical and mental condition was mapped using questionnaires and standardized memory tests. They also underwent a bicycle test and ultrasound was used to measure the blood flow in the cerebral blood vessels. 

Weijs: 'During the study, these 28 participants aged from around 70 to 80 years old. We studied a relatively healthy group: they were still fit enough to participate in the follow-up study. We did not diagnose any form of dementia in any of them, but 14 of the 28 indicated that they had developed mild memory problems in those ten years.'  

Unique in this study is that the researchers investigated changes in cerebral blood flow in the longer term. This is important because these changes are difficult to detect, especially in relatively healthy older people. They then linked these changes to the development of early memory complaints. This stage precedes the development of dementia. Weijs continues: 'That is why our findings provide better insight into the role of cerebral blood flow in the development and prediction of cognitive disorders. This offers perspective for our search for better prevention and treatment of dementia.'  

Lower blood flow

The researchers found no significant decrease in cerebral blood flow. However, when they split the group, a significantly stronger decrease was found in the participants with developed memory complaints. This blood flow to the brain is important: the better blood flows to an organ, the better it functions. This is no different for the brain: the better the blood flow, the more oxygen and nutrients reach the brain. This prevents brain cells from dying, causing loss of function.  

The researchers also looked at the regulatory mechanisms behind this cerebral blood flow. They explored cerebrovascular CO2 reactivity, how well the vessels respond to changes in the concentration of carbon dioxide (CO2) in the blood. That turned out to deteriorate with age. Another mechanism was dynamic cerebral autoregulation: this normally ensures that the blood flow to the brain remains constant in the event of fluctuations in blood pressure. This self-regulation improved remarkably in the participants in the study, especially in those who developed memory problems. Weijs cannot yet give a clear explanation for this, but suspects that there is a compensation strategy.  

The chicken or the egg dilemma

The big question now is: is lower blood flow due to a brain disease such as dementia, which means that there is less 'demand' for good blood flow? Or does damage to the vessels and thus lower blood flow lead to an increased risk of dementia? It's like the chicken or the egg dilemma, says geriatrician Jurgen Claassen of Radboudumc. Previous research, conducted by Weijs, showed that people with Alzheimer's have seen a strong decrease in cerebral blood flow, especially in the areas in which the disease was most active. ‘So that suggests: first brain damage, then decrease in blood supply. But we also know from other research that a lack of blood flow causes brain damage. Both chicken and egg.’ 

One thing is certain, and that is that lifestyle factors have a major impact on the health of our blood vessels. For example, smoking, high blood pressure and little exercise have a negative effect. Controlled blood pressure keeps the vessels healthy and reduces the risk of dementia by 20 to 30 percent. Weijs: 'More exercise, for example in the form of sports, is not always easy for older people. However, sitting less is usually possible, and may provide considerable health benefits. Studies show that older people spend a very large part of the day sitting. Especially older people with cognitive impairment. That is why we are placing more and more emphasis on research into the importance and effects of a decrease in sedentary behavior.' 

Whether we can actually prevent dementia with a healthy lifestyle cannot yet be said with certainty. Although there is evidence in this direction, many larger, long-term studies have to confirm this, following people for ten or fifteen years. 

About these publications

This article appeared in The Journal of Cerebral Blood Flow & Metabolism: Cerebrovascular CO2 reactivity and dynamic cerebral autoregulation through the eighth decade of life and their implications for cognitive decline – Ralf Weijs, Madelijn Oudegeest-Sander, Maria Hopman, Dick Thijssen, Jurgen Claassen. DOI: 10.1177/0271678X231219568.  

This article appeared in Geroscience: A decade of aging in healthy older adults: longitudinal findings on cerebrovascular and cognitive health – Ralf Weijs, Madelijn Oudegeest-Sander, Janneke Vloet, Maria Hopman, Jurgen Claassen, Dick Thijssen. DOI: 10.1007/s11357-023-00790-w. 

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