A GROUNDBREAKING study involving Plymouth researchers indicates passive smoking causes dementia.

The first large-scale study to suggest second-hand smoke exposure could lead to dementia and other neurological problems has been published in the British Medical Journal.

Research was undertaken by academics from the city's Peninsula Medical School, the University of Cambridge and the University of Michigan.

Dr Iain Lang from the Peninsula Medical School said: "These findings are of enormous public health importance, for two reasons.

"First, a lot of people smoke cigarettes and it's important that they are fully aware of the harm they do to themselves, and others, by smoking.

"Second, the rapidly growing numbers of older people in the population mean that it's crucial to identify and take action on factors that can reduce the risk of developing cognitive problems," he said.

The research team examined saliva samples from almost 5,000 non-smoking adults over the age of 50, using data from the 1998, 1999 and 2001 waves of the Health Survey for England and the English Longitudinal Study of Ageing.

The researchers say the link between second-hand smoke and cognitive impairment could be explained by the fact that heart disease increases the risk of developing dementia, and that exposure to second-hand smoke is known to cause heart disease.

Dr Lang said: "This is the first time that anyone has used biological measures of exposure to second-hand smoke to show that passive smoking is bad for the human brain.

"While the ban on smoking in public places has gone some way to mitigate this problem, there is still a risk from smoking at home.

"We hope that our findings will encourage smokers to change their behaviour in order to reduce the risk to others."

The Peninsula Medical School is a joint entity of the University of Exeter, the University of Plymouth and the NHS in the South West of England, and a partner of the Combined Universities in Cornwall.