What are the claims?
Long-term research studies have demonstrated that high blood pressure in mid-life is a key factor that can increase your risk of developing dementia in later life, particularly vascular dementia. These findings highlight that a lifelong approach to good health as the best way to lower your risk of dementia.
What is high blood pressure?
Blood pressure measures the force applied to your arteries (the major blood vessels that carry blood to our essential organs) as blood is circulated around the body by the heart. It is measured by your GP using a blood pressure cuff or with a 'self-service' machine, which is available at some GP practices. Your blood pressure is reported as two numbers. The first represents the systolic pressure, a measure of the pressure on your arteries per beat of the heart. The second is the diastolic pressure, a measure of the remaining pressure when the heart rests between beats. A normal blood pressure reading is around 120/80 mmHg.
High blood pressure, also known as hypertension, is diagnosed when your blood pressure is consistently above 140/90 mmHg. It is a serious condition that is a major cause of heart attack and stroke worldwide. By 2025, it is estimated that 1.56 billion people globally will be diagnosed with high blood pressure.
The known risk factors for high blood pressure include lack of exercise, being overweight or obese, an unhealthy diet that is high in salty food, alcohol consumption that exceeds the recommended maximum, drinking a lot of caffeine, smoking, a family history of high blood pressure, use of steroid medication, kidney disease and being of African or Caribbean descent.
What does the research say about high blood pressure and dementia?
According to the World Alzheimer Report 2014, multiple studies following large groups of people for 15-40 years have demonstrated that individuals who had high blood pressure in mid-life (usually characterised as people who are around 40-64 years of age) were more likely to develop vascular dementia in later life. Vascular dementia is the second most common form of dementia after Alzheimer's disease. It is caused by reduced blood flow to the brain, which starves brain cells of the oxygen and nutrients they need to function correctly. The association between high blood pressure and Alzheimer's disease is currently unclear.
However, despite this apparent link between vascular dementia and high blood pressure, the results from randomised controlled trials into whether lowering blood pressure can prevent dementia have so far been inconclusive.
This research demonstrates the importance of conducting studies that follow individuals over a long period of time (called longitudinal studies), to connect a person's lifestyle choices and health profile throughout their life to the risk of disease development in later life.
How does high blood pressure affect brain function?
There are several mechanisms by which high blood pressure affects the brain. High blood pressure causes a great deal of strain on the arteries over time, and this in turn causes the wall of the arteries to become thicker and stiffer as well as narrower. This is called arteriosclerosis. Fats found in the blood also contribute to the development of the narrowing of the arteries. This narrowing of the arteries can happen in the brain, causing a lack of essential nutrients and oxygen, which can damage brain cells and prevent them from functioning correctly.
High blood pressure is also the strongest risk factor for stroke. The most common cause of stroke is the blockage of the arteries in the brain (ischaemic stroke) and half of these are caused by hardening of the arteries. Another important cause of stroke is the bursting of an artery in the brain, causing what is known as a haemorrhagic stroke, also called bleeding in the brain. Both type of strokes cause brain cell death that can lead to the development of stroke-related or post-stroke vascular dementia.
Narrowing of the blood vessels especially deep inside the brain does not always cause an overt stroke. These very small deep blood vessels can be blocked or have small bleeds (microbleeds). The person may not feel anything wrong at the time, but the gradual accumulation of these changes over the years becomes visible on the brain scan and is called small vessel disease. This is a major contributing factor in the development of subcortical vascular dementia.
How can I control my blood pressure?
It is important to first get an accurate idea of what your blood pressure is. In England, it is estimated that 30% of the population have high blood pressure but, due to the lack of symptoms, it may go undiagnosed until a severe cardiac event (for example a heart attack or angina) occurs. Finding out your blood pressure can be easily done through a visit to your GP or by visiting a blood pressure booth in your local pharmacy and the NHS recommends that it should be checked every five years.
There are things you can do to lower your blood pressure if it is too high. One way is through a series of lifestyle changes that include losing weight, exercising regularly, maintaining a healthy diet that is low in salt, reducing caffeine and alcohol consumption, and quitting smoking. Alternatively, high blood pressure can be controlled through the use of blood pressure medication, which is prescribed by your doctor. These blood pressure lowering drugs have been shown to be safe and effective. However it is important to note that they have not been proven or recommended to directly prevent vascular dementia. There is a great deal of research into finding potential therapies that may be able to slow down or prevent development of vascular dementia.
If you have high blood pressure, it is important to talk to your doctor before attempting any lifestyle changes or trying new medication so they can provide you with personalised recommendations and monitor your progress.
A key take away message from these longitudinal research studies is that a life-long approach to health is important. Keeping blood pressure levels normal is only one factor, along with exercise, diet, smoking, and alcohol consumption that is important to consider when attempting minimising your risk of developing dementia. High blood pressure does not give you any symptoms initially so it is important to be proactive and find out what your blood pressure is.