Hypertension, or high blood pressure, increases the risk of vascular dementia primarily because it damages the blood vessels in the brain, leading to impaired blood flow and brain tissue injury. This damage disrupts the brain’s delicate vascular system, which is essential for delivering oxygen and nutrients to brain cells, and over time, these vascular changes contribute to cognitive decline and dementia.
To understand why hypertension raises the risk of vascular dementia, it helps to first grasp what vascular dementia is. Vascular dementia is a type of cognitive impairment caused by problems in the blood vessels supplying the brain. Unlike Alzheimer’s disease, which is linked to abnormal protein buildup, vascular dementia results from reduced or blocked blood flow that causes brain cells to die or malfunction. The brain depends on a constant, well-regulated blood supply, and when this is compromised, brain regions responsible for memory, thinking, and behavior suffer damage.
Hypertension affects the brain’s blood vessels in several key ways:
1. **Damage to Small Blood Vessels (Small Vessel Disease):** High blood pressure puts excessive force on the walls of small arteries and arterioles in the brain. Over time, this causes thickening, stiffening, and narrowing of these vessels, a condition known as small vessel disease. This reduces blood flow to critical brain areas, leading to tiny, often unnoticed strokes called microinfarcts. These microinfarcts accumulate and disrupt brain networks involved in cognition.
2. **White Matter Changes:** The brain’s white matter consists of nerve fibers that connect different brain regions. Hypertension-related small vessel disease causes damage to this white matter, visible as white matter lesions on brain scans. These lesions interfere with communication between brain cells, impairing cognitive functions such as attention, processing speed, and executive function.
3. **Blood-Brain Barrier Disruption:** The blood-brain barrier is a protective layer that controls what substances can enter the brain from the bloodstream. Hypertension can cause this barrier to become leaky, allowing harmful molecules and inflammatory cells to enter the brain tissue. This leakage promotes inflammation and further damages brain cells and blood vessels.
4. **Arterial Stiffness and Reduced Vascular Compliance:** Chronic high blood pressure leads to arterial stiffness, meaning the large arteries lose their elasticity. Normally, elastic arteries help cushion the pulsatile flow of blood from the heart. When arteries stiffen, the pulsatile pressure is transmitted more forcefully into the delicate microvasculature of the brain, causing microvascular injury and increasing the risk of hemorrhages and ischemic damage.
5. **Cerebral Hypoperfusion:** Hypertension can cause narrowing and blockage of larger arteries due to atherosclerosis (plaque buildup). This reduces overall cerebral blood flow, leading to chronic cerebral hypoperfusion—insufficient blood supply to the brain. Prolonged hypoperfusion starves brain cells of oxygen and nutrients, causing cell death and brain atrophy, especially in regions like the hippocampus that are critical for memory.
6. **Stroke and Transient Ischemic Attacks (TIAs):** Hypertension is a major risk factor for stroke, which directly causes brain injury. Strokes can be large or small, but even small strokes increase the risk of vascular dementia by damaging brain tissue and disrupting neural networks. Repeated strokes or TIAs compound this damage, accelerating cognitive decline.
7. **Promotion of Amyloid-β Accumulation:** Although vascular dementia is primarily caused by vascular damage, hypertension may also contribute indirectly to Alzheimer’s-type pathology by promoting amyloid-β protein accumulation in cerebral blood vessels (cerebral amyloid angiopathy). This worsens vascular dysfunction and increases the risk of microbleeds and infarcts.
The combined effect of these processes is a progressive decline in brain structure and function. The brain’s ability to compensate for vascular injury diminishes over time, leading to noticeable cognitive symptoms such as memory loss, difficulty planning or organizing, slowe
