Heart to Head: Cardiovascular health and Alzheimer’s  

While Alzheimer’s is a neurodegenerative illness characterized by the death and dysfunction of brain cells, researchers and physicians have long suspected a connection between Alzheimer’s and broader cardiovascular health. Now, new findings are beginning to support this connection, bringing it into clearer, scientific focus.

It’s no mystery that good blood flow is essential for brain wellness and function. Indeed, vascular dementia, or cognitive impairment caused by the brain not getting enough blood, is the second leading kind of dementia following dementia caused by Alzheimer’s. The two types of dementia often get confused, even misdiagnosed as one another. To make things even more complicated, most people have a “mixed” dementia, with evidence of Alzheimer’s pathology, vascular damage in the brain, and pathology associated with Alzheimer’s and Lewy Body Dementia on autopsy. However, of the two, vascular dementia is definitely caused by various blood supply problems.

Thus far, no evidence proves that cardiovascular problems cause Alzheimer’s. Yet increasing evidence indicates they play a role in the disease.

A Strong Association
Several recent studies highlight the relationship between Alzheimer’s and various cardiovascular risk factors. One observational study looked at more than 800 people who already showed mild cognitive impairment, but not necessarily early-stage Alzheimer’s. It found that those with vascular risk factors, such as high cholesterol, hypertension, cerebrovascular diseases and diabetes, were twice as likely to develop Alzheimer’s as those with no risk factors. This study also found a lower incidence of Alzheimer’s among people who had these risk factors treated compared to those who did not.

Another study looked at a sample of 37,000 people from one hospital system. It found that patients with atrial fibrillation, a common type of irregular heartbeat, were 44% more likely to develop Alzheimer’s than those without it. A follow-up study found that the most common treatment for atrial fibrillation, catheter ablation, reduced Alzheimer’s risk.

High cholesterol correlated with increased Alzheimer’s risk in another study, which sampled nearly 10,000 patients who had had their cholesterol measured between ages 40 and 45. People who had high cholesterol (249 – 500 mg/dL) in middle age were one and a half times more likely to develop Alzheimer’s later in life than those with normal levels.

A Possible Synergy
Why might there be this relationship? One possibility is that cardiovascular problems increase stresses on neuronal processes, perhaps helping to tip them out of balance. Recent work with animal models indicates that vascular stresses on the brain promote the production and reduce the clearance of excess amyloid beta, the hallmark of Alzheimer’s. In turn, excess amyloid beta further aggravates problems in the brain’s blood supply, degrading vessels and increasing lesions. This suggests that excess amyloid and vascular problems may work together, along with processes such as oxidative stress, to magnify destructive effects both before and during Alzheimer’s onset.

A Surprising Finding
In a recent breakthrough finding, scientists examining heart failure in an animal model discovered amyloid-like plaques in weakened heart muscle cells. Because these plaques were very similar to those seen in Alzheimer’s patients, this finding suggests that the biochemistry of heart failure and Alzheimer’s may have more in common than we previously believed. While the finding is highly preliminary, especially in its relation to Alzheimer’s, it holds great promise for our understanding of both Alzheimer’s and heart failure.

Testing Possible Treatments, Taking Positive Steps
The significant links between cardiovascular health and Alzheimer’s have led researchers to investigate some cardiovascular-oriented treatments as possible Alzheimer’s therapies. However, our understanding of how these might interact with the disease remains incomplete. Attempts to treat Alzheimer’s using anti-cholesterol drugs highlighted this knowledge gap. Many had thought these drugs, known as statins, would slow Alzheimer’s. But statins had no effect on the disease in controlled clinical trials.

Despite this notable disappointment, Alzheimer’s researchers continue to study substances with cardiovascular benefits. One study now underway examines resveratrol, a key cardioprotective substance in some types of red wine. Omega-3s, the fatty acids prevalent in the Mediterranean diet, are another such substance being investigated for possible Alzheimer’s benefits.

How should a person respond to these findings on cardiovascular health and Alzheimer’s? So far, it’s difficult to pinpoint any single cardiovascular factor, substance or behavior as a magic bullet for preventing or treating Alzheimer’s because we still don’t understand enough about what causes the disease. At the same time, the evidence suggests that maintaining general heart-healthy behaviors including eating a good diet, exercising, not smoking, having regular checkups, treating existing problems and controlling cholesterol, correlates with significantly reduced Alzheimer’s risk and, in some studies, even slower disease progression.

Jamie Bennett is a freelance writer and a student in the Writing Division, Columbia University School of the Arts.

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