Brain vascular changes, such as small vessel disease, are quite common during ageing and they have been shown to increase our risk for dementia, in particular Vascular Dementia. But do such brain vascular changes always lead to dementia? The short answer is no, the changes increase our risk for dementia considerable but they do not make it definite that we will develop dementia in the future.
But how do brain vascular changes actually emerge and how do they increase our risk for dementia?
Let’s find out.
The question of whether brain vascular changes lead to dementia came recently up from a conversation with @juliagapowell on my Twitter account (@DementiaScience). Thank you, Julia! It is a really great question as many people fear that having such changes will lead to dementia but that is not necessarily the case. But let’s start from the beginning.
What are brain vascular changes?
Brain vascular changes are disease changes in the blood vessels in our brain. The main vascular disease changes in the brain are related to stroke. There are two main types of stroke we can have: haemorrhagic and ischemic.
A haemorrhagic stroke is essentially a rupture or leak of a blood vessel, leading to blood flowing out of the blood vessel into the brain. Compare it to a water pipe burst, which means that if we open the tap no water is coming out because it is leaking somewhere else causing damage. It is the same in the brain where a haemorrhagic stroke not only causes damage by blood flowing into the brain but also the brain areas which usually get their blood from these blood vessels, do not get any or very reduced blood flow. Haemorrhagic strokes in the brain become more common during ageing as our arteries (the blood vessels carrying oxygen-rich blood) are becoming less flexible or even harden. This means that if we have high blood pressure, our arteries are more likely to rupture when we age, causing potentially haemorrhagic strokes. This hardening or stiffening of the arteries is also referred to as atherosclerosis/ arteriosclerosis and can be further increased by our lifestyle factors, such as consuming too much bad cholesterol food or smoking.
Atherosclerosis/ arteriosclerosis can also contribute to ischemic strokes. But instead of having a ruptured and leaking blood vessel as in the haemorrhagic stroke, for the ischemic stroke, the blood vessel gets internally blocked which again reduces or stops the blood flow to the brain areas where it is needed. Again, think about a water pipe, but this time the water pipe is not leaking but blocked somewhere, there would be again no water coming out of the tap. Especially fatty deposits from too high cholesterol can accumulate in the major arteries and if such deposits dislodge they can block brain arteries causing a blockage and eventually an ischemic stroke. A final common reason for blockages of the brain arteries is caused by little blood clots. These little blood clots can occur when people have age-related heart conditions, such as atrial fibrillation, which is a condition where the atrium (a chamber in our heart) ‘flutters’/fibrillates red blood cells to clump together. These blood clots are then pumped through the body and can cause an ischemic stroke in the brain. Atrial fibrillation is a very common but treatable condition and should be therefore taken seriously as if it is untreated can lead to potential strokes in the brain.
In summary, strokes (haemorrhagic and ischemic) disrupt the blood flow to the brain causing potential significant damage to nerve cells.
Why is it important to maintain blood flow to brain areas?
One important aspect to understand is that the brain is one of the major consumers of blood of the whole body. To put this in relation, the brain only account for ~2% of our body weight but needs ~20% of our blood to function normally. In essence, the brain requires an enormous amount of blood to function normally. The reason is that the brain is physiologically very active, as our nerve and other brain cells are continously active, needing oxygen and glucose (sugar) to maintain their activity. The oxygen and glucose are provided by the blood, which explains why blood flow to the brain is so critical to normal functioning and a disruption of blood flow, such as by a haemorrhagic or ischemic stroke, can cause a devastating effect on our brain. Even a reduce flow or temporary flow stop can cause the nerve and other brain cells to be severly affected and even die. The nerve cell death in turn will affect the cognitive function in the area affected by the reduced/stopped blood flow, resulting in cognitive symptoms in people.
This leads us very nicely onto the relationship with dementia. Even Alois Alzheimer recognised that blood vessel changes can result in cognitive changes in older people and might be a significant contributor to the development of dementia. Let’s not forget that dementia is defined as a syndrome (a group of related symptoms) associated with an ongoing decline of brain functioning. For most dementias, this ongoing decline of cognitive brain function is due to the accumulation of proteins in and around the nerve cells, causing them eventually to die. Not so for vascular dementia, where the nerve cells death and associated cognitive changes are due to the changes in blood flow to the brain. This is a very important factor to understand, as it clearly distinguishes vascular dementia from any other dementia, which is all caused by protein accumulations.
Speaking of vascular dementia, the term vascular dementia is now considered to be too restrictive by the scientific community, instead, the broader term Vascular Cognitive Impairment (VCI) is now the preferred term. Vascular dementia is regarded as a severe form of vascular cognitive impairment. This change in terminology has not yet made its way into clinical guidelines and practice but will likely happen in the future. In the meantime, if you read about vascular dementia or vascular cognitive impairment, do not worry both refer to the same changes cause by vascular pathophysiology. In fact, it is exactly the realisation that brain vascular changes do not lead always to dementia, which was part of changing the terminology to vascular cognitive impairment, as vascular changes lead to cognitive impairment but not necessarily dementia. As said earlier, having brain vascular clearly increases our risk for dementia but does not mean we will develop dementia definitely.
How much does the risk for dementia increase if we have brain vascular changes?
A very good question which is not that easy to answer, as it depends a bit on which brain vascular changes we have as well as our age. First off, the type of brain vascular changes makes a difference to our increased risk of vascular dementia. According to the current guideline, vascular dementia can be classified into four major subtypes: 1) post-stroke dementia, defined as dementia emerging within 6 months after a stroke. With stroke we mean here a stroke that causes significant changes to someone, such as weakness in one side of the body and face or language problems (speaking or understanding speech). These larger strokes can be either ischemic or haemorrhagic.; 2) subcortical ischemic vascular dementia, defined as mini-strokes happening in the deeper (subcortical) regions of the brain. With our new stroke knowledge, we already know that the ischemic label tells us that these strokes are caused by a blockage to the blood vessel supplying the deeper (subcortical) regions of the brain. The key difference the post-stroke dementia is that these subcortical strokes are often ‘silent’, meaning that they are not resulting in major symptoms as the large strokes. This makes these ‘silent’ strokes even more dangerous, as we do not know that they are happening and if many happen symptoms will eventually emerge; 3) multi-infarct (cortical) dementia, defined as mini-strokes occurring in the upper (cortical) regions of the brain. Similar to the subcortical mini-strokes, the multi-infarct dementia strokes are ‘silent’ with only a significant amount causing symptoms. On brain scans those mini-strokes look like little holes peppered across the cortical brain regions; and finally, 4) mixed dementia, defined as a combination of vascular dementia and Alzheimer’s disease. Personally, I think the term ‘mixed dementia’ is very unfortunate, as it suggests that all types of dementias are somehow ‘smooshed’ together, whereas, in fact, it is ‘only’ the co-occurence of vascular dementia and Alzheimer’s disease. But there we are, terminology is often a minefield.
The actual risk for each of these different types of vascular cognitive impairment is actually still being established. For example, to establish the risk of ‘silent’ mini-strokes is difficult at it is often only detected once people get a diagnosis of vascular dementia. The most reliable data has been established for post-stroke dementia, for which the data shows that around 1 in 10 people develop dementia following a major stroke within a year following the stroke. As I said, the risk for the ‘silent’ subcortical and cortical strokes is much harder to establish as they only lead to cognitive symptoms once people have a significant amount of such mini-strokes in the brain.
A final key factor to understand is that these cardiovascular stroke events occur more commonly, the older we get. At the same time, age is also the major risk factor for dementia, the older we get the more likely it is we develop dementia. Since both cardiovascular and dementia changes co-occur with ageing it can be difficult to delineate which one came first or which one caused the increased cognitive symptoms. There has been even the suggestion that one should ‘weigh’ the occurrence of cardiovascular against dementia changes by age. This sounds a bit too scientific/abstract, so let’s explain this a bit more. Weighing by age means we would put more emphasis on one or the other factor by age. For example, if we have someone in their 60s who has significant vascular changes in their brain and develops cognitive changes, should we attribute the vascular changes as the main factor for the cognitive changes, instead of, for example, Alzheimer’s disease? By contrast, if we have someone in their 90s who has significant vascular changes in their brain and develops cognitive changes, should we attribute the cognitive changes more to dementia, such as Alzheimer’s disease, since vascular brain changes are extremely common at that age? Such questions are currently discussed but are not easy to answer but will make a difference as to how vascular dementia will be diagnosed and treated in the future.
The good news is that we already know very well how to treat cardiovascular disease and risk factors. In turn, this means that we can reduce our risk for vascular dementia significantly with existing treatments, medications and lifestyle changes. In fact, we can reduce our risk for dementia overall by up to 30% by simply focusing on cardiovascular risk factors, which is, in my opinion, an astonishingly high number for risk reduction. Not surprisingly, the classic lifestyle changes, such as improved cardiovascular fitness, balanced diet, weight within the average range, limited alcohol intake, no smoking all are excellent in improving our cardiovascular fitness. On top of that, medication to treat hypertension (high blood pressure) or hypercholesteremia (high cholesterol) can also make a big difference, since we know now that these factors can potentially cause haemorrhagic and ischemic strokes and ‘silent’ mini-strokes. In light of these well-established risk factors, the American Heart Association/American Stroke Association recommends checking our health status via seven key factors (nonsmoking, physical activity according to recommended guideline levels, healthy diet consistent with current guideline levels, body mass index (BMI) of less than 25, blood pressure <120/80 mm Hg, total cholesterol <200 mg/dl, and fasting blood glucose <100 mg/dl) to maintain optimal brain health. Adjusting to these parameters will make it much less likely for us to develop significant brain vascular changes, resulting in vascular cognitive impairment or even vascular dementia. I recommend, therefore, to everyone, whether they have the first cognitive changes or not to check those factors regularly, adjust their lifestyle factors and talk to their doctor about how they can best improve their cardiovascular health and in turn, reduce their risk for vascular dementia.
The take-home message is that even if we have vascular changes to our brain we can reduce our risk for dementia significantly and will not necessarily develop dementia. It is a message worth spreading.