Gardens in care homes could be crucial in helping to stimulate memories for dementia sufferers, scientists have found.

Researchers at the University of Exeter Medical School found green spaces helped care home residents relax, and reduced agitation for those with dementia.

The study, published today in the Journal of the American Medical Directors Association, considered the findings of 17 different pieces of research.

Lead researcher Rebecca Whear said: "There is an increasing interest in improving dementia symptoms without the use of drugs. We think that gardens could be benefiting dementia sufferers by providing them with sensory stimulation and an environment that triggers memories.

"They not only present an opportunity to relax in a calming setting, but also to remember skills and habits that have brought enjoyment in the past."

The research represents the first attempt to bring together findings from a range of studies and has also highlighted several factors that must be overcome if gardens are to be useful in the future care of dementia patients.

These include understanding possible hazards that a garden might represent to residents, and ensuring staff have time to let residents enjoy an outdoor space to its full potential.

Residents at 11 UK care homes were included in the research, as well as services in America, China and Europe.

Supported by the National Institute for Health Research Collaboration for Applied Health Research and Care South West Peninsula, the review also found that gardens could offer welcome spaces for interactions with visitors, helping to stimulate memories for dementia patients while providing well-being opportunities for families and staff.

Almost half of the elderly people living in residential care have dementia or dementia symptoms, a figure which increases to more than three-quarters in nursing homes.

Despite its positive findings, the study's authors were keen to point out that this area of research is currently understudied and undervalued by policy makers.

Dr Ruth Garside, an expert in evidence synthesis and one of the paper's authors, said: "There's a lot we don't know about how a garden's design and setting influences its ability to affect well-being, yet it's clear that these spaces need to offer a range of ways of interacting - to suit different people's preferences and needs.

"We want to pursue these answers to ensure that care experiences can be maximised for sufferers of dementia, their carers and families."

There are currently 800,000 people with dementia in the UK, although there are thought to be in excess of 400,000 people who have the condition but have not been diagnosed.