A new study suggests high blood pressure may lead to reductions in brain volume and higher levels of white matter brain lesions, but not with reduced cognition or one of the key proteins associated with Alzheimer's disease.

Researchers tracked blood pressure from ages 36-69 to explore its influence on the brain, and found that the link may be there from a younger age than anticipated.

The authors suggest that blood pressure monitoring and interventions may need to start at, or before, the age of 40 to maximise later brain health.

Lead author Professor Jonathan M Schott, of University College London, said: "Our research builds on existing evidence around the role of blood pressure and subsequent brain pathology.

"We found that higher and rising blood pressure between the ages of 36 and 53 had the strongest associations with smaller brain volume and increases in white matter brain lesions in later life.

"We speculate that these changes may, over time, result in a decline in brain function; for example, impairments in thinking and behaviour, so making the case for targeting blood pressure in mid-life, if not earlier.

Blood pressure in mid-life has previously been linked to a higher risk of dementia but how this happens, and when blood pressure is most important, is not fully understood, researchers say.

To address these questions, the team followed 502 individuals from the MRC National Survey of Health and Development (NSHD), who were all born in the same week in 1946.

The participants were free from dementia at the start of the study and 465 underwent brain scans to assess their brain health.

All participants had blood pressure measured at 36, 43, 53, 60-64, and 69 years old, and blood pressure changes between the readings were calculated.

The brain scans looked for levels of a key Alzheimer's protein, amyloid, in the brain, said the study, published in The Lancet Neurology journal.

They also assessed the size of the brain - an indicator of brain health - and the presence of blood vessel damage in the brain.

According to the results, higher blood pressure at the age of 53 and faster rises in blood pressure between 43 and 53 were associated with more signs of blood vessel damage or "mini strokes" in the brain when an individual was in their early 70s.

Researchers also found that higher blood pressure at the age of 43 and greater increases in blood pressure between the ages of 36 and 43 were associated with smaller brain volumes.

However, blood pressure was not associated with the amount of amyloid protein in the brain and did not appear to predict memory and thinking problems at this age.

Prof Schott, from the UCL Queen Square Institute of Neurology, said: "The findings suggest that blood pressure even in our 30s could have a knock-on effect on brain health four decades later."

Co-author Dr Josephine Barnes, of UCL, said: "As increases in blood pressure and higher blood pressure between the ages of 36 and 53 seem to have a detrimental effect on brain health in later life, these findings reinforce the need for monitoring blood pressure even before mid-life."

The authors highlight several limitations including that the participants were exclusively white British people, and additionally slightly under-represents people with poor overall health.

The individuals included in the analyses were cognitively normal, and, as only a few individuals in their early 70s have cognitive decline, the authors believe that the cognitive effects of the brain changes they observed may be seen later in life.

Dr Carol Routledge, director of research at Alzheimer's Research UK, which funded the original study, said: "High blood pressure in mid-life is one of the strongest lifestyle risk factors for dementia, and one that is in our control to easily monitor and manage.

"Research is already suggesting that more aggressive treatment of high blood pressure in recent years could be improving the brain health of today's older generations.

"We must continue to build on this insight by detecting and managing high blood pressure even for those in early mid-life."

Australian Associated Press