A disease that affects nearly half of Americans increases the risk of Alzheimer’s, a study suggests.
Older people who have untreated high blood pressure are about one-third more likely to be diagnosed with Alzheimer’s disease.
Around 120 million people suffer from high blood pressure, caused by a variety of factors, including poor diet, lack of exercise, smoking, genetics and age. However, only a quarter of them have it under control.
High blood pressure can be difficult to treat, simply because many people don’t know they have it, as it often has no symptoms. It’s nicknamed “the silent killer.”
It causes damage to blood vessels, restricting blood and oxygen flow to the brain and depriving it of its ability to remove the toxic protein buildup that is a hallmark of Alzheimer’s.
High blood pressure causes blood vessels to constrict. The heart has to work harder to pump more blood, but narrowed blood vessels prevent oxygen from reaching the brain, which is thought to underpin the link to Alzheimer’s.
The benefits of maintaining healthy blood pressure levels (aim for 120/80) for heart health are well known and well documented.
But the link between Alzheimer’s and this disease hasn’t been clear until now. Now, an NIH-supported study is seeking to shed more light on the connection.
Researchers at the University of New South Wales in Australia combined data from 14 unique studies involving 31,250 people from a variety of countries, including Australia, Brazil, China, France, Germany, Greece, Italy, Japan, Korea, Nigeria, Republic of the Congo, Spain, Sweden and the United States.
The average age of people enrolled in the studies was 72, although researchers considered Alzheimer’s risk in adults as young as 60.
Each person in the studies was followed for an average of four years, and 1,415 of them developed Alzheimer’s.
The researchers recorded each person’s blood pressure levels, whether they had diagnosed hypertension and whether they were taking medications to treat it.
They found that 9 percent had untreated high blood pressure, 51 percent were taking blood pressure medications, 36 percent did not have high blood pressure, and 4 percent were classified as uncertain.
After adjusting for variables such as a person’s age, sex and education level, the researchers found that individuals with untreated high blood pressure had a 36 percent higher risk of developing Alzheimer’s compared to those with normal blood pressure.
Adults age 60 or older with untreated high blood pressure had a 42 percent higher risk of Alzheimer’s compared with those who had high blood pressure but were taking medication.
Dr Matthew Lennon, a dementia researcher at the University of New South Wales and an author on the paper, said: ‘Our meta-analysis involving people from around the world found that taking blood pressure medication was associated with a lower lifetime risk of Alzheimer’s disease.
‘These results suggest that treating high blood pressure as a person ages remains a crucial factor in reducing the risk of developing Alzheimer’s disease.’
The report was published in the journal Neurologythe medical journal of the American Academy of Neurology.
High blood pressure and heart disease go hand in hand.
A variety of factors, including genetics, age, diet, physical activity level, obesity, smoking history, and stress, can contribute to high blood pressure.
The exact way in which high blood pressure occurs remains a mystery for doctors and researchers. It appears that it can develop through several different processes.
One way this happens is when the body absorbs too much salt from an unhealthy diet, which causes the volume of blood in the body to increase.
Another way is when the body’s system for regulating blood pressure (the renin-angiotensin-aldosterone system or RAAS) doesn’t work properly.
Additionally, if the nervous system is overactive, it can also contribute. All of these conditions cause blood vessels to constrict, forcing the heart to work harder to pump blood.
When a person’s blood pressure is consistently 130/80 mmHg or higher, a doctor will usually diagnose them with hypertension.
Blood pressure readings show two numbers that reflect diastolic and systolic pressure. Diastolic pressure refers to the force of blood in the arteries when the heart is relaxed between beats. It is the number on the bottom.
Systolic pressure is the number at the top and measures the pressure in the arteries during one heartbeat.
This chart shows the prevalence of high blood pressure among American adults by age and sex. (Source: Heart Disease and Stroke Statistics: 2020 Update: A Report from the American Heart Association)
The link between hypertension and Alzheimer’s remains a very active area of scientific research, but scientists have identified some key connections.
In addition to damaged blood vessels preventing oxygen from reaching the brain, hypertension is a major risk factor for stroke caused by a lack of oxygen to the brain. This level of oxygen deprivation, specifically in the left hemisphere of the brain, can lead to vascular dementia.
High blood pressure also stimulates an inflammatory response throughout the body that inflicts oxidative stress on the organism.
This is thought to play a role in the progression of Alzheimer’s by damaging brain cells and accelerating the buildup of harmful amyloid plaques and tau tangles commonly seen in brains affected by the disease.
While the researchers cautioned that their findings do not prove that high blood pressure causes Alzheimer’s, only that there is a connection, they suggested that too few people are taking steps to mitigate their risk of neurological diseases later in life.
Dr Lennon said: “High blood pressure is a major cause of stroke and cerebrovascular disease, yet it can be controlled with medication, reducing the risk of these diseases.”