Exercise could prevent Alzheimer's by triggering hormone which helps regrow brain cells, study suggests

Sarah Knapton
The hormone irisin is produced in exercise and helps to stimulate new brain cells in the hippocampus, an area associated with memory and learning 

Exercise could protect against Alzheimer's by triggering a hormone which helps regrow brain cells, a study has found. 

Scientists have known for some time that exercise reduces the risk of developing dementia, but did not know if there was a direct link or whether ill people were simply unable to work out.

Now a new series of studies had shown that a hormone released during exercise, called irisin, is depleted in the brains of people with Alzheimer’s, and can protect animals against memory loss and brain damage.

Mice who swam nearly every day for five weeks did not develop memory impairment despite getting infusions of beta amyloid - the brain-cell clogging protein implicated in Alzheimer's.

It suggests not only that exercise really does protect against dementia, but also that a drug which mimics irisin could be the answer to preventing the disease.

"I would certainly encourage everyone to exercise, to promote brain function and overall health," said Dr Ottavio Arancio, professor of pathology and cell biology and of medicine at Columbia University.

"But that's not possible for many people, especially those with age-related conditions like heart disease, arthritis, or dementia.

“For those individuals, there's a particular need for drugs that can mimic the effects of irisin and protect synapses and prevent cognitive decline."

There are currently 850,000 people living with dementia in Britain and that figure is expected to rise as the population ages.

But despite decades of research and trials, no drug has yet been found to reverse or prevent the condition, and several major drugs companies have now pulled out of testing altogether.

Recent research has shown that the hormone irisin promotes brain cell growth in the hippocampus, a region of the brain associated with memory and learning. Only two areas of the brain can regrow brain cells in adulthood, and the hippocampus is one of the first areas to deteriorate in people suffering from Alzheimer’s disease.

"This raised the possibility that irisin may help explain why physical activity improves memory and seems to play a protective role in brain disorders such as Alzheimer's disease" added Dr Arancio.

Using tissue samples from brain banks, they found that irisin is present in the human hippocampus and that hippocampal levels of the hormone are lower in individuals with Alzheimer's.

Animal studies looking into the impact of irisin on the brain, found that it protects brain synapses and memory. When irisin was disabled in the hippocampus of healthy mice, synapses and memory weakened. Boosting brain levels of irisin improved both.

Similarly blocking irisin with a drug completely eliminated the benefits of swimming on memory, the researchers also found.

Mice who swam and were treated with irisin-blocking substances performed no better on memory tests than sedentary animals after infusions with beta amyloid.

The scientists are now searching for pharmaceutical compounds that can increase brain levels of the hormone or can mimic its action.

The research was published in Nature Medicine.

Sign up for your essential, twice-daily briefing from The Telegraph with our free Front Page newsletter.