LACK of exercise, smoking and an unhealthy diet increase the risk of developing dementia, according to new international guidelines on how to fight the disease.

Although the World Health Organisation report found that age is the most common driver behind increasing incidence, it also stressed that changes in lifestyle could reduce the likelihood of cognitive decline.

A huge review of existing evidence found that physical inactivity, smoking, unhealthy diet and excessive alcohol consumption significantly increased the threat of the disease.

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The WHO said is supported advice that "what is good for our heart is also good for our brain".

Medical conditions such as diabetes, high blood pressure, high cholesterol, hearing loss, obesity and depression were also played a role in cognitive decline and the development of dementia.

However, in the case of factors such as depression or hearing loss, there was insufficient evidence to prove that treatment would prevent or slow the disease.

Although it noted that good social participation and support are strongly connected to good health and wellbeing throughout life, the WHO did not find sufficient evidence that increased social interaction reduced the risk of cognitive decline and dementia.

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The strongest preventative measures appeared to be increased physical activity among healthy adults, management of high pressure and diabetes through drug treatments, and smoking cessation.

There was also evidence in support of consuming a Mediterranean-style diet high in fish, olive oils, fruit, vegetables, nuts, wholegrains and legumes such chickpeas and lentils.

Dr Tedros Adhanom Ghebreyesus, WHO director-general, said: “In the next 30 years, the number of people with dementia is expected to triple. We need to do everything we can to reduce our risk of dementia.”

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In Scotland, more than 90,000 people are currently living with dementia, but this is expected to climb to 164,000 by 2036.

There are currently no treatments which can stop or reverse its symptoms.

Jim Pearson, director of policy and research from Alzheimer Scotland, welcomed the new guidelines.

He said: "This adds to the increasing body of evidence that changes to our lifestyles can potentially reduce the risks of developing dementia.

"These include keeping physically, mentally and socially active and maintaining a healthy diet.

"Generally speaking what’s good for your heart can also be good for your brain.

"Scotland is leading on key research in this area, but overall, we need more research into the causes of dementia, the care of people living with dementia and potential future treatments, as well as seeking to prevent or find a cure."

Robert Howard, professor of old age psychiatry at University College London, said the guidelines were "sensible but unsurprising" - but that even sticking to them would not be a game-changer.

He added: "Keep on doing the things that we know benefit overall physical and mental health, smoking cessation, reduce harmful alcohol drinking, treat hypertension, eat a healthy balanced diet and lose weight if you are obese, but understand that the evidence that these steps will reduce dementia risk is not strong."