Researchers say rates of the disease could be halved if related environmental factors – such as a lack of sunlight – which trigger the increased risk can be identified.
A study carried out by scientists at the University of Edinburgh focused on mapping the incidence of the disease in twins in Sweden.
It revealed those living in the north were two to three times more likely to develop dementia compared with those in the south, when factors such as age, gender and genes were taken into account.
Another study used data gathered from a nationwide survey of children born in 1921 to examine the risk of developing dementia.
This research found that while there was no change linked to where people lived as children, by the time men and women reached middle-age there was once again a higher risk for those who lived in areas further north, such as Grampian, compared to regions in the south, such as the Borders.
Tom Russ, clinical lecturer in old age psychiatry at Edinburgh University’s Alzheimer Scotland Dementia Research Centre, said a lack of vitamin D could be one possible reason for the link.
“The north-south divide does make you think about latitude and it may be it is something to do with sunlight exposure and vitamin D – that is a possibility and it has certainly been linked to healthy brain function and dementia,” he said, adding: “The next step is to pin down what these factors could be.
“Given that two to threefold variation, it is not going to be one factor – but if you could identify what these factors are and optimise them in the whole population, you could potentially halve dementia rates.”
Russ said the Swedish study of twins allowed any genetic factors which might explain the north-south divide to be “taken out of the picture”.
He added: “In the Scottish study, everybody was born in 1921, so they will have experienced different things all at the same time – for example, they will all have been the same age when the NHS was introduced. By middle age – around 50 or 60 years old – there was a big variation across Scotland [in dementia rates] and it was a similar pattern: higher in the north and lower in the south.”
Lindsay Kinnaird, research manager at Alzheimer Scotland, said: “We’re delighted that Scotland is leading the way in helping us to understand what causes this illness.
“If we are able to identify environmental risk factors, then we have the opportunity to make adaptations to lifestyle that can minimise their impact.”