A surprising study by a team of UK researchers says people with dementia should avoid intense physical activities.

Physical exercises do not slow down mental decline in people already diagnosed with dementia, and can even make it worse, according to a new study published on Thursday.

A team of UK researchers wrote in the British Medical Journal that they do not recommend moderate to high-intensity exercise as a treatment option for dementia.

Dementia is an umbrella term that includes Alzheimer’s disease, which describes a deterioration of mental ability such as memory, language, and ability to focus.

Nearly 47.5 million people have dementia in the world, and many believe that regular exercises might prevent or delay mental illness. But recent experiments showing contradictory results have challenged this popular idea.

To resolve the confusion, the scientists discovered that four months of moderate to high intensity exercise training does not slow down the progress of dementia.

“I was disappointed by the results, although I probably wasn’t completely surprised,” said Sarah Lamb, lead author of the study and professor of trauma rehabilitation at Oxford University. “I think it would be fair to say that dementia is a difficult problem to fix,” she told The Guardian.

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Almost 500 people with dementia – with the average age of 77 and across 15 regions of England – volunteered to participate in the trial. Among them, 329 were randomly assigned to the exercise programme while 165 received usual care.

The exercise group went to the gym twice a week for four months and exercised for an additional hour each week. Surprisingly, the exercise group had the worse score for Alzheimer’s disease assessment, but the difference was small – 1.4 percent – and the importance is uncertain.

The physical training helped the participants in the exercise group gain short-term physical fitness, but they did not witness any improvement in their daily living life or health-related quality of life, the study said.

Lamb said this study should not stop people from taking people with dementia for walks, swimming or other sports, because low-intensity workout is still beneficial to patients. “We know that gentle exercise is good for you. We don’t want people to stop what they are doing,” she said.