A study has revealed that while physical exercise may prevent dementia, it does not delay mental decline in people after they’ve been diagnosed.

It is generally believed that exercise can delay the onset of Alzheimer’s and other forms of dementia.

However, researchers reported something contrary in The BMJ medical journal.

They took 494 people in England who had been diagnosed with dementia, and assigned 329 of them to an exercise programme.

The researchers said they took part in 60-90-minute group sessions in a gym twice a week for four months, and home exercises for an additional hour per week.

The average age of the group was 77, according to the report.

The researchers noted that cognition had declined in both the exercise and non-exercise groups.

According to a press statement, in the exercise group, the decline was steeper, “however, the average difference was small and clinical relevance was uncertain.”

Brendon Stubbs of King’s College London’s Institute of Psychiatry, commenting on the study, said its findings was “enormously important” for the care of people with Alzheimer’s disease.

“Whilst previous smaller studies have suggested that exercise can prevent or improve cognitive decline in people with Alzheimer’s disease, this robust and very large study provides the most definitive answer we have on the role of exercise in mild-moderate Alzheimer’s disease,” he said via the Science Media Centre.

“The search for effective lifestyle interventions that can delay cognitive decline in dementia must continue.”