AIR pollution and a shortage of sunshine may increase the risk of dementia, Scottish research has revealed.

Experts at Edinburgh University have drawn-up a shortlist of environmental hazards which might make people more prone to illnesses such as Alzheimer's Disease.

Exposure to traffic and factory fumes and a lack of vitamin D - which is created when skin is exposed to sunlight - are among the commonplace problems which may play a part in developing the condition.

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There is also some evidence pesticides and minerals found in drinking water could have a role, although the findings are mixed.

The scientists say there is not yet sufficient information to draw any solid conclusions and are calling for further investigation.

Dr Tom Russ, of the Alzheimer Scotland Dementia Research Centre at Edinburgh University, said mystery surrounded the cause of around a third of dementia cases.

He explained high blood pressure, obesity, diabetes, smoking, lack of exercise and low educational attainment had all been linked to dementia.

He said: "Probably together they explain about a third of the risk. Genetics is another factor - that is another third. But there is still one third of dementia risk which is not explained. We think it is plausible environmental risk factors explain that third. The important thing about them is, you can do something about them."

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Aiming to prevent or delay the onset of dementia, his team at Edinburgh University reviewed dozens of studies that have considered the issue.

Among them a study of more than 19,000 women living in different parts of the United States which suggested smog and other air pollutants may contribute to memory loss and dementia. It found former nurses in their 70s scored lower on tests of memory and thinking if they lived in areas with the poorer air quality.

A report from Germany also found older women who lived near busy roads performed worse on memory and thinking tests than similar women who lived in rural areas.

Dr Russ said examining the geographical variation in the prevalence of dementia in Scotland and Sweden had found a division between the north and sunnier south.

Meanwhile, a British study of 1,658 over 65s revealed those with very low levels of vitamin D in the blood were more than twice as likely to develop dementia.

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Dr Russ said more research was needed to find out whether vitamin D and pollution were actually causing dementia and how.

His research was funded by Alzheimer Scotland and the findings published in the journal BMC Geriatrics.

Jim Pearson, director of policy and research at Alzheimer Scotland, said the study substantially improved knowledge and understanding.

He continued: "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."

Dr Russ said people interested in reducing their dementia risk are advised not to smoke, take measures to avoid obesity and diabetes - or keep diabetes well controlled - look after their blood pressure and take some exercise.

Dementia is considered a major global public health crisis that is expected to grow as people live longer. Almost 47 million people live with dementia worldwide and this is predicted to increase to more than 131 million by 2050.

Estimates indicate the disease costs the UK more than £26 billion annually and worldwide dementia care costs exceed the market value of Google or Apple each year.