New research based on a large longitudinal study has revealed that reduced blood flow from the heart in old age also leads to poorer circulation in the temporal lobes of the brain, which constitute our memory "hub."
A study led by researchers at Vanderbilt University in Nashville, TN — in collaboration with other institutions — was published yesterday in the journal Neurology. The findings show that older adults with a lower cardiac index, or the blood flow pumped from the heart, is tied to reduced cerebral blood flow in a region of the brain key to our memory.
Study co-author Dr. Angela Jefferson explained for Medical News Today that she and her team became interested in the link between cardiac index measurements and cerebral blood flow after some of their previous research revealed a correlation with cognitive impairment diseases such as Alzheimer's.
"Our prior research findings," she told us, "have shown reductions in cardiac function are related to abnormal brain changes in older adults, including cognitive impairment, Alzheimer's disease, and dementia."
Following those findings, she added, "The purpose of the current study was to investigate the link between cardiac index and cerebral blood flow to better understand possible mechanisms underlying our prior clinical observations."
Poor brain circulation is like 'advanced aging'
The research team analyzed the data of 314 participants in the Vanderbilt Memory & Aging Project, a longitudinal study focused on "vascular health and brain aging." The participants were 73 years old, on average, 59 percent of them were male, and 39 percent of them had been diagnosed with mild cognitive impairment (MCI).
According to the National Institute on Aging, around 8 out of 10 individuals with MCI later go on to develop Alzheimer's disease.
Following these tests, Dr. Jefferson and team ascertained that a low cardiac index was tied to reduced cerebral blood flow. This was especially true for the temporal lobes, which are known to play a key role in memory creation and storage.
In the left temporal lobe of the brain, the blood flow was reduced by 2.4 milliliters, on average, for 100 grams of tissue per minute, for each unit decrease in cardiac index. In the right temporal lobe, there was an average reduction of 2.5 milliliters of blood for 100 grams of tissue per minute.
To ensure the consistency of their results, the scientists adjusted for confounding variables, such as the MCI diagnosis, the participants' age, their level of education, and the presence of the ApoE e4 gene, which is associated with an increased risk of developing Alzheimer's disease.
"The primary finding," Dr. Jefferson said, "was that lower cardiac index related to lower cerebral blood flow in the temporal lobes, the brain's memory center and the area where Alzheimer's disease first develops in the brain."
"The magnitude of these associations corresponded to 15 to 20 years of advanced aging."
Underlying mechanisms still unclear
The researchers admit that their study also has some limitations, including the fact that the results do not clearly explain causality, making it possible that reduced cerebral blood flow may be the cause and not the effect.
Moreover, the population sample on which the scientists focused was predominantly made up of white, healthy, and well-educated adults, which may mean that the results would differ for other groups.
"[The] effects are based on associations across hundreds of people, so we are limited in what type of individual clinical recommendations we can make," Dr. Jefferson told us.
She emphasized that the findings of the current study are yet another indication of how important it is to look after cardiovascular health later in life, as it could have wide-ranging effects. "That being said," she added, "it is increasingly well-recognized that there is an important connection between heart health and brain health."
"Managing blood pressure and diabetes, maintaining a healthy weight, and regular physical activity are a few of the things older adults can do to maintain good heart health, which may have very important implications for preserving good brain health," she recommended.
Dr. Jefferson continued, "We believe this study offers an initial step in identifying mechanisms linking heart health and brain health."
"Once confirmed, we hope these mechanisms will offer new prevention or treatment strategies for conditions characterized by cognitive impairment, such as Alzheimer's disease and dementia."
Dr. Angela Jefferson
The next step from here, Dr. Jefferson told MNT, will be to "continue to track [the participants'] cardiovascular health status and cognitive abilities."
This, she hopes, will allow the team to gain a better understanding of the mechanisms that connect heart and brain health, and how they may impact cognition later in life.
"Following these older adults over time," Dr. Jefferson said, "offers important future opportunities to investigate mechanisms linking cardiovascular integrity with abnormal brain changes in older adults, including memory loss and cognitive impairment."