Longevity Briefs: Understanding The Link Between Heart Disease And Dementia

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: People with cardiovascular diseases (CVD) are more likely to get dementia. Studies suggest that up to a third of Alzheimer’s disease cases (the most common form of dementia) might be caused by modifiable risk factors for CVD, such as high blood pressure and obesity. Cardiovascular function is critical for the brain: neurons are very metabolically active and are therefore sensitive to a reduced supply of oxygen. High blood pressure can also damage small blood vessels in the brain and lead to oxygen deprivation and tissue damage.

Even though we know this relationship exists, not many studies have actually attempted to look in detail at how CVD and its risk factors affect the brain long-term.

What did the researchers do: In this study, researchers looked at data from 4184 Spanish participants aged 40-54 who did not have diagnosed CVD, cancer or any lifespan-shortening chronic disease at the start of the study in 2010. Participants were exhaustively screened for cardiovascular risk factors and for subclinical atherosclerosis every 3 years. Atherosclerosis is the most common form of CVD, in which fatty plaque formation leads to a progressive narrowing of blood vessels. Subclinical atherosclerosis refers to blood vessel narrowing that has not progressed to CVD – almost all adults will have some degree of subclinical atherosclerosis.

Those participants who were found to have subclinical atherosclerosis above a certain threshold were then assigned to brain PET scans (positron emission tomography) at the start of the study and again after three years. By introducing small amounts of radioactive sugar (glucose) into the blood, researchers could see how much glucose was being metabolised by different brain regions.

Key takeaway(s) from this research:

• Higher cardiovascular risk score was associated with reduced glucose metabolism in people with subclinical atherosclerosis.
• The growth of atherosclerotic plaques in the carotid artery was associated with a decline in glucose metabolism independently of risk score.
• These changes were found to affect brain regions of interest in the progression of Alzheimer’s disease.
• It’s unknown whether the observed decline in glucose metabolism affected cognitive function or Alzheimer’s risk.

First, researchers looked at how cardiovascular risk score (which was calculated based on factors like blood pressure, age and cholesterol) related to brain glucose metabolism in brain regions most affected by Alzherimer’s disease (such as the hippocampus). They found that between the first and second scans, glucose metabolism in these regions declined by about 4.3% in those with the highest risk scores throughout the study, compared to about 1.5% in those with the lowest risk scores.

Next, researchers looked to see if there was a relationship between atherosclerotic plaque growth and decreased glucose metabolism in brain regions of interest. They found that participants with faster growing plaques in their carotid arteries (which supply blood to the brain) had a greater annual decline in brain glucose metabolism. This relationship was significant after the researchers accounted for the fact that people with larger plaques also had higher cardiovascular risk scores.

This study reinforces previous evidence about the link between CVD and dementia, and provides a more detailed look at the mechanisms behind it. Perhaps the biggest takeaway is that in people who do not have heart disease, the growth of atherosclerotic plaques in the carotid artery may still have an impact on the brain that could potentially increase the risk of Alzheimer’s, though this study didn’t measure whether Alzheimer’s risk or cognitive function was actually affected. This study also doesn’t tell us why glucose metabolism was reduced in people with more atherosclerosis, though reduced blood flow to the brain is likely to play a role.

It should be noted that this study selected participants who had a threshold level of subclinical atherosclerosis, and that only 16% of participants were female, both of which may limit the generalisability of the findings.