A condition suffered by nearly half of all Americans raises their risk of Alzheimer's disease, a study suggests.
Seniors who have untreated high blood pressure are about a third more likely to be diagnosed with Alzheimer’s disease
About 120 million people have high blood pressure, caused by a range of factors including poor diet, lack of exercise, smoking, genetics, and age. But only around a quarter of them have it under control.
High blood pressure can be difficult to treat simply because many might not know they have it, as it often has no symptoms. Its nickname is ‘the silent killer’.
It causes damage to blood vessels, restricting blood flow and oxygen to the brain and depriving it of its ability to clear out toxic protein buildup which 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 impede oxygen from getting to the brain, believed 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 condition’s link to Alzheimer’s has been less clear. Now, an NIH-backed study seeks to shed more light on the connection.
Researchers at the University of New South Wales in Australia combined data from 14 unique studies encompassing 31,250 people from a range of countries, including Australia, Brazil, China, France, Germany, Greece, Italy, Japan, Korea, Nigeria, Republic of Congo, Spain, Sweden, and the United States.
The average age of the people who enrolled in the studies was 72, though researchers considered Alzheimer’s risk in adults as young as 60.
Each person across the studies was monitored for an average of four years, and 1,415 of them developed Alzheimer’s.
Researchers noted each person’s blood pressure levels, whether they had diagnosed hypertension, and whether they were taking medications to treat it.
They found 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 noted as uncertain.
After adjusting for variables such as the person’s age, sex, and level of education, 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 60 and over with untreated high blood pressure had a 42 percent higher risk of Alzheimer’s compared to those who had high blood pressure but were taking medication.
Dr Matthew Lennon, a dementia researcher at the University of New South Wales and author of the paper, said: ‘Our meta-analysis that included people from around the world found that taking blood pressure medications was associated with decreased risk of Alzheimer’s disease throughout later life.
‘These results suggest that treating high blood pressure as a person ages continues to be a crucial factor in reducing their risk of Alzheimer’s disease.’
The report was published in the journal Neurology, the medical journal of the American Academy of Neurology.
High blood pressure and heart disease go hand in hand.
A range of factors, including genetics, age, diet, physical activity level, obesity, smoking history, and stress, can all contribute to high blood pressure.
How exactly high blood pressure occurs remains a question among doctors and researchers. It appears to be able to develop through a few different processes.
One way is when the body absorbs too much salt from an unhealthy diet, the volume of blood in the body is increased.
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 overly active, it can also contribute. All of these conditions cause blood vessels to constrict, making the heart work harder to pump blood.
When a person’s blood pressure is consistently 130/80 mmHg or higher, a doctor will typically diagnose them with hypertension.
Blood pressure readings show two numbers, reflecting the diastolic and systolic pressures. Diastolic refers to the force of blood in the arteries when the heart is relaxed between beats. It’s the number that appears on the bottom.
Systolic pressure is the number on the top and measures the pressure in the arteries during a heartbeat.
This chart shows the prevalence of high blood pressure among US 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 is still a highly active area of scientific research, but scientists have identified some key connections.
In addition to damaged blood vessels keeping oxygen from 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 spurs a whole-body inflammatory response which inflicts oxidative stress on the body.
This is believed to play a role in the progression of Alzheimer’s by damaging brain cells and speeding up the accumulation of harmful amyloid plaques and tau tangles often seen in brains afflicted with the disease.
While the researchers cautioned that their findings don't prove that hypertension causes Alzheimer's, only that there is a connection, they suggested that too few people are taking the steps necessary to mitigate their risk of neurological diseases down the line.
Dr Lennon said: ‘High blood pressure is a leading cause of stroke and cerebrovascular disease, and yet it can be controlled with medication, reducing a person’s risk of these diseases.’
