A systematic review published in The Cochrane Library, included data from eight trials involving 329 people that showed that exercise could improve cognitive functioning.
Also, data from six studies involving 289 people showed that exercise could improve the ability of older people with dementia to carry out daily activities, such as walking short distances or getting up from a chair.
The study updates a Cochrane review carried out in 2008, when only four trials on the effects of exercise in older people with dementia were available.
"In our previous review, we were unable to draw any conclusions about the effectiveness of exercise in older people with dementia, due to a shortage of appropriate trials," said researcher Dorothy Forbes, an Associate Professor of Nursing who works at the University of Alberta in Edmonton, Alberta.
"Following this new review, we are now able to conclude that there is promising evidence for exercise programmes improving cognition and the ability to carry out daily activities. However, we do still need to be cautious about how we interpret these findings," Forbes said.
The researchers remain cautious because there were substantial differences among the results of individual trials.
In addition, they did not find enough evidence to determine whether exercise improved challenging behaviours or depression in older people with dementia.
They were unable to come to any conclusions regarding quality of life, or benefits for family caregivers and health systems, because there was not enough evidence.
"Clearly, further research is needed to be able to develop best practice guidelines to enable healthcare providers to advise people with dementia living at home or in institutions," said Forbes.
"We also need to understand what level and intensity of exercise is beneficial for someone with dementia," Forbes said.