The research, which is published in Brain Communications, is part of the Insight46 study, which has been collecting health data from over 450 people since their birth in 1946.

The team explored how leisure time physical activity patterns over the course of 30 years affected brain health – particularly early markers of Alzheimer’s disease – and cognition at the age of 70.

They found that being physically active, especially before the age of 50, is linked to a larger hippocampus (the area of the brain mainly responsible for memory).

People who exercised throughout life* were also less likely to experience cognitive decline, even if they had key markers of Alzheimer’s such as amyloid build-up and brain shrinkage. This was especially true for women.

Understanding more about how exercise physically changes the brain and potentially protects people from dementia could lead to new interventions in the future, that can stop the condition from happening in the first place.

Lead author, Dr Sarah-Naomi James (Dementia Research Centre, UCL Queen Square Institute of Neurology, and MRC Unit for Lifelong Health and Ageing at UCL) said: "Our findings show that staying active throughout your life, especially before turning 50, can help keep your brain healthy and delay early signs of Alzheimer's. This is especially true for women.
“We hope that our work will highlight the critical importance of exercising to support brain health for people of all ages."

As part of the Insight46 study, the team collected information on how frequently a person self-reported taking part in physical activity for leisure across 30 years, before and after they turned 50. The team then analysed brain scans taken when the participants were 70 years old, to see if physical changes in the brain were linked to lifelong exercise.

Dr James’ team found that people who said they exercised once or more a month before they were 50 years old, tended to have less shrinking in the brain’s memory centre, the hippocampus. This area is often the first brain region affected in Alzheimer’s disease.

Being physically active wasn’t directly related with other Alzheimer’s disease markers in the brain, like amyloid plaques or overall brain shrinkage. However, being active helped those with early Alzheimer’s disease markers to maintain and buffer their cognitive function, particularly for women.

Evidence suggests that keeping our brains healthy can help build ‘cognitive reserve and resilience’, helping to maintain memory and thinking in older age for longer. This is despite the brain aging and having signs of Alzheimer’s disease.

Again, this beneficial effect was even more prominently in women. Those who had signs of Alzheimer’s disease in their brain, but who were active in the past were more likely to have better cognitive function than those who were always inactive.

The team are now calling for further research to explore what aspects of leisure time physical activity may be driving this relationship. This could in the future be used as a preventative intervention for Alzheimer’s disease.

Dr James said: “Exercise is essential for keeping our brains healthy. But we are still building a picture around what physical changes happen in the brain to protect it against dementia.
“Insight46 has given us valuable clues to what changes are happening in the brain, opening new exciting research avenues.
“More work will be crucial to fully understand how exercise, and taking part in leisure activities throughout our lives could be a powerful tool to protect people against dementia for as long as possible.”

This study was principally funded by grants from Alzheimer’s Research UK, the Medical Research Council Dementias Platform UK and the Wolfson Foundation.

David Thomas, Head of Policy and Public Affairs at Alzheimer’s Research UK, said: “Dementia is not just an inevitable part of aging, and finding ways to prevent people from ever developing it is a vital part of our mission for a cure.
“Research shows that nearly half of dementia cases can be prevented or delayed by addressing health and lifestyle risk factors. This means there are things that all of us can do to reduce our risk, such as keeping physically active. 
“Studies like Insight46 have highlighted not just what factors influence brain health, but also what point in a person’s life these factors have the most impact.
“While there is no sure-fire way to prevent dementia, there are some things within our control that can reduce our risk, including keeping active and looking after our heart health, challenging our brains and keeping connected to the people around us. The evidence shows that it’s never too early or late to start making positive changes.”

Graham’s story:

Alzheimer’s Research UK supporter Graham Kent, 74, has a particular motivation for looking after his health. His wife, Marie, was diagnosed with Alzheimer’s in 2019 so Graham is determined to exercise regularly to help reduce his risk of dementia.

Graham said: “Because of Marie’s Alzheimer’s, I want to make sure I’m around for as long as possible to look after her. Part of that means staying fit and active to help keep my brain healthy.
“The first thing I do in the morning is go out for a run with our dog. And I train with a friend at least once a week. It’s great to run with people because you keep each other accountable and stay connected with them at the same time.
“Running is good fun because I know that every time I’m exercising, it’s good for my heart and my brain. I can’t control getting older, which I know increases a person’s risk of getting dementia, but I know that I can exercise regularly to help keep my brain healthy for as long as possible.”

Study limitations

The study's limitations include the reliance on self-reported leisure-time physical activity, which doesn't account for occupational or other physical activities, and the *lack of objective measures like exercise intensity or duration. Additionally, there was a higher dropout rate among disadvantaged participants, which may affect the generalisability of the findings.

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