Image copyright Getty Images Image caption Air pollution is included in the shortlist of environmental risk factors that may contribute to dementia

A shortlist of environmental factors that may contribute to the risk of developing dementia has been drawn up by experts.

The list includes exposure to air pollution and a lack of vitamin D, although researchers warned that there are not yet any solid conclusions.

It has been put together by Edinburgh University's Alzheimer Scotland Dementia Research Centre.

The centre believes future research should focus on the shortlist.

Dementia is known to be associated with lifestyle factors such as high blood pressure in mid-life, smoking, diabetes, obesity, depression and low educational attainment, as well as genetic factors.

But the Edinburgh researchers said a third of dementia risk was unexplained, and they want to determine whether other issues are at play, including the environment.

Previous studies

The team reviewed dozens of previous studies that considered environmental risk factors linked to dementia.

They found that a lack of vitamin D - produced by the body through exposure to sunlight - and exposure to air pollution were implicated, along with occupational exposure to some types of pesticide.

The research suggested that excessive levels of minerals found in drinking water may also be linked to the disease, but the evidence was mixed.

Dementia facts

Dementia is a major global public health crisis expected to grow as people live longer

Almost 47 million people live with dementia worldwide - predicted to increase to more than 131 million by 2050

90,000 people in Scotland have the disease

Estimates indicate the disease costs the UK more than £26bn annually

Worldwide dementia care costs exceed the market value of Google or Apple each year

There is a growing consensus among doctors that a significant proportion of cases could be prevented or delayed by addressing environmental factors linked to the disease.

The team behind the latest research said future studies should focus on the short list of environmental risk factors flagged up in their study.

'Important new area'

Dr Tom Russ, of the Alzheimer Scotland Dementia Research Centre, said: "Our ultimate goal is to prevent or delay the onset of dementia.

"Environmental risk factors are an important new area to consider here, particularly since we might be able to do something about them.

"We found that the evidence is particularly strong for air pollution and vitamin D deficiency. But we really need more research to find out whether these factors are actually causing dementia and how, and if so, what we can do to prevent this."

Jim Pearson, director of policy and researcher at Alzheimer Scotland, said: "The research study substantially improves our knowledge and understanding of environmental factors which may increase the risk of developing dementia and provides a basis for further, and more focused, research in this area.

"Dementia is a global public health priority. There are 90,000 people living with dementia in Scotland and the number is on the rise.

"We need much more research into the causes of dementia, treatments and supports that allow people to live well with dementia as well as the prevention and cure of dementia."

The research, published in the journal BMC Geriatrics, was funded by Alzheimer Scotland.