The negative effects of vascular health on long-term brain structure and function at middle age
The authors of a research study, published in the journal Neurology, reported that having certain vascular risk factors in midlife correlated with decreases in brain structure and a decline in cognitive function. The vascular risk factors they examined were high blood pressure, diabetes, smoking, and obesity. As we age, we may develop these risk factors, which could negatively influence our brain health. The results of this study also have important implications related to dementia.
In this study, researchers used several tests that are known to be predictors of dementia. To examine brain structure, they used various MRI markers of aging: they measured the total volume of the brain, the volume of the hippocampus — a brain structure important for memory, and they measured a type of lesion in the brain that is a marker of vascular disease and may be indicative of cognitive dysfunction, particularly in older populations. To test cognitive ability, the researchers used a number of psychological tests of both verbal and visual memory, and select tests of cognitive function. The researchers then analyzed the data statistically to estimate relationships between each of the vascular risk factors and the changes in people’s brain structure and performance on cognitive tests. Over 1,300 people who did not have dementia took part in this study.
In general, there were greater changes in brain structure and cognitive abilities as study participants aged. Participants were about 54 years old when scientists measured their vascular risk factors. This was a longitudinal study conducted over a decade, so participants were aged between 61 and 67 years old, on average, when scientists subsequently measured changes in their brain structure and cognitive ability. The researchers reported that there were greater changes in brain structure for participants aged 65 years and older: the rate at which they developed vascular lesions was much greater for these individuals.
Having vascular risk factors in midlife predicted a decrease in the size of the hippocampus — a brain structure important for memory.
Differences in results between men and women
There were some differences in brain structure results between women and men. About an equal number of women and men took part in the study. The average decrease in total brain volume over each year was significantly greater for men than for women. Additionally, the research suggested that men had a greater decline in the volume of the hippocampus than women.
Vascular risk factors affect brain structure and cognitive function
Each of the vascular risk factors were associated with an unfavourable change in brain structure or cognitive function, and in some cases, unfavourable changes in both brain structure and cognitive abilities.
Having high blood pressure in midlife was associated with adverse changes in brain structure. Specifically, it was associated with an increased rate of developing vascular brain lesions, which is a marker of vascular disease and cognitive dysfunction. Having high blood pressure in midlife was also associated with impairments in people’s cognitive abilities. In these study participants, scientists saw a decline in executive function, which is a set of cognitive processes that we use to manage ourselves and to manage resources to reach a goal.
The researchers also reported that having diabetes or smoking in middle age was associated with decreases in brain structure, particularly, a greater decrease in the size of the hippocampus. Smoking in midlife was associated with further changes in brain structure – it predicted a greater decrease in the total volume of the brain. The study also reported that smoking in midlife was associated with an increased risk of having a greater expansion of vascular lesions in the brain.
Being obese in midlife was associated with a greater risk of a decline in cognitive abilities. Specifically, being obese was associated with an increased risk of being in the top 25% of study participants who had a decline in executive function. Also, having a greater waist-to-hip ratio was associated with a decrease in brain structure, specifically, a reduction in the total volume of the brain.
Summary of findings
Overall, researchers reported that having vascular risk factors in midlife predicted a decrease in the total volume of the brain, a decrease in the size of the hippocampus, a decline in cognitive function, and an increase in the rate at which vascular brain injury progressed.
Knowing that vascular risk factors affect brain structure and cognitive abilities is important because many of these risk factors can be mitigated by lifestyle choices and medical treatments.
Risk of Developing Dementia
In previous research studies, scientists reported that middle-aged people who have high blood pressure or diabetes, who smoke, or who are obese may be at a higher risk of developing dementia. It was unclear though which parts of the brain, specifically, were affected. The researchers wondered whether these vascular risk factors affected brain structure or cognitive function. This study advances our understanding by providing evidence that both brain structure and cognitive function are negatively affected in middle-aged participants who have these vascular risk factors.
Another way this study adds to our knowledge relates to the longitudinal nature of the study design, which took place over a decade. For example, previous studies reported associations between smoking and decreased brain volume at a given moment in time. In this study, data was collected from the same subjects over a 10-year period. This study also expands our understanding when vascular risk factors are present in a middle-aged population and how it relates to cognitive ability. While other studies found associations between vascular risk factors and cognitive ability, the risk factors were measured at the time of the cognitive assessment and not in midlife.
This study contributes to a body of scientific knowledge that suggests associations between having cardiovascular risk factors and adverse changes in brain structure, cognitive function, and an increased risk of developing dementia.
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