The brain changes could have an impact on the risk of developing dementia in later life the team from Oxford University said.
The trial involved using medical data and brain scan information from 22,000 people from across the UK.
The findings showed there was significant structural changes in the grey and white brain matter among those people who had either diabetes or high blood pressure.
Further investigation found those individuals did not do well in tests carried out to measure their thinking speed and short-term memory.
Professor Masud Husain, an expert in neurology and cognitive neuroscience at the Nuffield Department of Clinical Neurosciences at Oxford University, said: “Remarkably, the findings show that it is possible to detect the negative effect of cardiovascular risk factors, such as raised blood pressure and diabetes, on cognitive function and brain structure in otherwise healthy people.
“The major implication is that these risk factors don’t just have an influence on what happens later in life – the risk of developing dementia – they also have an impact on the brain and current levels of cognitive function in mid-life.”
The link between the two health conditions and the decline of the brain was more prevalent in people aged between 44 and 69. Surprisingly there was less impact in the over 70s. But the higher the blood pressure, the worse the problems got which indicates GPs should start treating even mild blood pressure to prevent long-term conditions.
Professor Husain said: “For blood pressure, every millimetre of pressure in your arteries counts, even in people who aren’t on any treatment.
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“We can detect that even small increases in blood pressure have an impact on the brain right now. It is not surprising that if this is allowed to continue untreated for decades, it might have a cumulative impact on brain structure and function, eventually making it vulnerable to dementia.”
The findings have been published in the Nature Communications journal.