Growing scientific evidence suggests disturbances in cardiovascular health can reverberate through the brain's intricate networks, altering its function. Cardiologists and neurologists are diving deeper into the heart-brain nexus and uncovering shared risk factors and pathways that link seemingly unrelated conditions like heart disease and dementia.
In a recent interview with wmnHealth, Dr. Deborah Levine, an internal medicine physician and professor at the University of Michigan, explored the heart-brain link in more detail. She discussed her research on cognitive decline following a stroke, and she highlighted the importance of understanding the interplay between cardiovascular health and brain function in addressing Alzheimer's disease, the most common form of dementia.
This interview has been lightly edited for length and clarity.
wmnHealth: A growing body of science suggests our brain health is inextricably linked to the heart. What has your research uncovered about the heart-brain connection?
Deborah Levine: There's a strong link between heart disease and brain health. Last year, my team published an exciting study showing that heart attacks are associated with faster cognitive decline, controlling for the change in people's cognitions before a heart attack. We have another paper currently being reviewed that suggests heart failure is linked to a quicker long-term cognitive decline compared to the level of cognitive decline a given patient would've experienced without heart failure. The important question we're deeply interested in answering—and continuing to investigate—is, "Why are heart conditions like heart attack or heart failure associated with faster cognitive decline over the long term?"
The important question we're deeply interested in answering—and continuing to investigate—is, "Why are heart conditions like heart attack or heart failure associated with faster cognitive decline over the long term?" —Dr. Deborah Levine, University of Michigan
We've also done some work on sex differences in dementia risk. It has shown that women, even without an incident of stroke, have higher initial cognitive scores but a much faster cognitive decline over time than men. However, the reasons for the decline are unclear —whether it's due to hormones, cardiovascular risk factors, or social factors like education.
You—and other researchers—are still investigating the underpinnings of heart disease and subsequent cognitive decline. Do you have any hypotheses about what mechanisms might be at play?
Levine: I think there are pathways in the brain and mechanisms outside of the brain that contribute. One factor is hypoperfusion, so if the heart is not pumping blood adequately to brain tissues, then that can cause damage and injury, ultimately accelerating cognitive decline.
There are also pathways in the brain that could be impacted after a heart attack and are playing a role in this cognitive decline. Studies have shown that there's a link between heart disease and increased levels of tau protein in the brain. This can trigger neurodegeneration, as we see in Alzheimer's disease. Another factor is ongoing vascular injury from shared risk factors that cause both heart disease and neurodegeneration, such as hypertension, diabetes, and tobacco use.
How heart disease might accelerate cognitive decline
Vascular Injury: Damage or abnormal changes to the blood vessels that supply the heart and brain can cause short-term or long-lasting problems with thinking and memory. For instance, atherosclerosis is a condition where arteries become narrow and stiff due to fat buildup, restricting blood flow. Another example of vascular injury is microvascular dysfunction, in which smaller blood vessels in the heart and brain don't work properly, affecting the delivery of oxygen and nutrients to the brain. This can trigger stress responses in brain cells, including the buildup of an abnormally folded protein called tau—a hallmark of Alzheimer's.
Inflammation: This is the body's natural response to injuries or infections. When it comes to heart disease, there's often lingering inflammation throughout the body, which has a domino effect on brain health. It causes neurons to degenerate and die off much faster, accelerating cognitive decline.
Disruption of Blood-Brain Barrier (BBB): This protective barrier regulates the passage of substances between the bloodstream and the brain. BBB dysfunction allows inflammatory molecules to sneak into the brain, exacerbating damage to neurons.
Tau Pathology: Heart disease can lead to disruptions in the body's autonomic nervous system. These changes influence how the tau protein acts in the brain, causing it to clump together and build up.
Shared Risk Factors: Heart disease and neurodegenerative diseases like Alzheimer's share a range of common risk factors, including hypertension, diabetes, and tobacco use. These risk factors independently contribute to both poor cardiovascular and brain health, ultimately setting the stage for cognitive decline and neurodegeneration.
When a patient has a stroke, is cognition an important focus for cardiologists and other clinicians providing care?
Levine: Guidelines recommend that stroke survivors should have their cognitive abilities evaluated. In the U.S., the Affordable Care Act includes the Medicare Wellness Benefit, which provides an annual wellness exam. A cognitive assessment is part of that. However, there have been very few studies looking at how much, in the long run, cardiologists are focusing on cognition after stroke, so that's something that remains to be investigated in depth.
Shared risk factors between heart disease and Alzheimer's
Hypertension: High blood can damage blood vessels throughout the body, including those in the brain. This can lead to an increased risk of neurodegenerative changes, including accumulation of tau protein in the brain.
Diabetes: Diabetes not only increases the risk of heart disease, but it also promotes glucose toxicity in cells and insulin resistance. This can cause irreversible damage to blood vessels in the brain.
Smoking: Using tobacco is another factor that contributes to vascular injury and inflammation. This can adversely affect both heart health and brain function.
Physical Inactivity: Lack of physical activity is associated with an increased risk of heart disease and is also a significant risk factor for cognitive decline and Alzheimer's.
