Having high blood pressure in later life could put you at greater risk of developing Alzheimer’s, a study found.
Older people with high blood pressure were almost half - 46 percent - more likely to have brain lesions - areas of damage linked to the disease.
They also had higher levels of tau tangles, a type of protein which harm the brains of people with Alzheimer’s disease.
The findings add to growing evidence that adopting healthier lifestyles could be key to staving off dementia.
High blood pressure - known by the medical term hypertension - affects one in three British adults and is one of the leading causes of heart attacks and stroke.
America's rate was deemed the same - with 75 million people (a third of the population) diagnosed with high blood pressure. But in January, new guidelines made a controversial recommendation to lower the threshold from 140/80 mmHg to 130/80 mmHg, adding another 31 million people to that bracket, to a total of 106 million.
There are often no symptoms until it is too late, with only around half of people even aware that they are at risk.
An ideal blood pressure is a reading of anywhere between 90/60 and 120/80 millimeters of mercury (mmHg).
Patients are normally diagnosed with high blood pressure and prescribed treatment only if the top reading - the systolic pressure - is above 140 mmHg.
Scientists from Rush Alzheimer’s Disease Center in Chicago wanted to examine the impact blood pressure changes in old age can have on the brain.
They studied almost 1,300 elderly people from the US, who had their blood pressure taken every year until they died, an average eight years later.
Two-thirds of those taking part already had high blood pressure, which is common in the elderly, with most (87 percent) participants on medication for it.
Researchers found those with above average systolic pressure -pressure when the heart beats- had a significantly higher risk of lesions, called infarcts.
These are areas of tissue death, caused by a lack of blood supply to the area, which can often be caused by blockages to the artery.
Those with very high blood pressure - defined as 147mmHG - had a 46 percent higher chance of large lesions and were more than a third (36 percent) more likely to have small lesions.
Higher than average diastolic pressure, when the heart rests between beats, had a 28 per cent higher risk of lesions, they found.
When the brain was examined post-mortem, researchers found a link between high blood pressure and brain tangles but not plaques, the other protein linked to the disease.
Taking blood pressure medications did not make any difference, according to the findings, published in the American Academy of Neurology.
Lead author Dr Zoe Arvanitakis said: ‘Blood pressure changes with aging and disease, so we wanted to see what kind of impact it may have on the brain.
‘We researched whether blood pressure in later life was associated with signs of brain aging that include plaques and tangles linked to Alzheimer’s disease, and brain lesions called infarcts, areas of dead tissue caused by a blockage of the blood supply, which can increase with age, often go undetected and can lead to stroke.’
Previous research has shown blood pressure causes strain on the arteries over time, resulting in artery walls becoming thicker, stiffer and narrower, making it harder for blood to get there.
Fats in the blood also cause narrowing of the arteries, leading to a lack of essential nutrients and oxygen, which can damage brain cells and prevent them from functioning correctly.
Experts suggest steps to lower blood pressure, such as drinking less alcohol, keeping a healthy weight, not smoking or eating too much salt, could prevent damage to the brain.
The authors noted limitations to the study including not having have access to blood pressure of participants in middle age, only in later life, and suggested further research is needed.
Dr Doug Brown, Chief Policy and Research Officer at Alzheimer’s Society, said high blood pressure in middle-aged is known to increase dementia risk in later life.
‘While this study linked raised blood pressure later in life to early changes in the brain associated with Alzheimer’s disease - a build-up of tangles - it was an observational study and we don’t know if the people studied had a diagnosis of Alzheimer’s disease so we cannot draw firm conclusions.
‘With the number of people diagnosed with Alzheimer’s ever growing, we need to look at all ways we can reduce the chance of getting dementia.
‘The next step could be to explore the effects of controlling blood pressure at a healthy level during mid and late life to see whether this can reduce the risk of developing Alzheimer’s.’