BEING exposed to other people's smoke could increase the risks of developing dementia, researchers said yesterday.
The scientists said second-hand smoke could cause damage to the way the brain works, making dementia more likely.
The study, published in the British Medical Journal, found that those exposed to high levels of other people's smoke were 44 per cent more likely to suffer cognitive impairment, affecting their memory and ability to perform calculations.
Previous research has established that smoking can increase a smoker's risk of dementia, but the latest study, led by Cambridge University, is the first to look at the effect of smoking on other people.
Dr David Llewellyn and his colleagues analysed data for more than 4,800 non-smoking adults aged 50 and over. They included some people who had been smokers but had given up.
The adults were split into four groups based on the levels of cotinine – a marker of nicotine exposure – in their saliva. Neuro-psychological tests were carried out on the volunteers to assess brain function.
These included tests of verbal memory – recalling words – numerical calculations, time orientation and verbal fluency, such as naming as many animals as possible in one minute.
On the basis of these tests, those whose scores were in the bottom 10 per cent were identified as suffering from cognitive impairment.
The results showed that, compared with the lowest levels of cotinine, those in the next group up were 8 per cent more likely to suffer cognitive impairment.
People in the next highest group were 13 per cent more likely to suffer cognitive impairment. And those in the highest concentration group were 44 per cent more likely to suffer cognitive impairment compared with those in the lowest group. The results were similar for people who had never smoked and those who had been smokers once but had given up.
The researchers said one reason for the link could be that smoking was linked to an increased risk of heart disease and stroke.
Dr Llewellyn said: "
Our results suggest that inhaling other people's smoke may damage the brain, impair cognitive functions, such as memory, and make dementia more likely.
"Given that passive smoking is also linked to other serious health problems, such as heart disease and stroke, smokers should avoid lighting up near non-smokers."
Rebecca Wood, the chief executive of the Alzheimer's Research Trust, said: "Previous research shows that smoking increases our risk of developing dementia, and this new study reveals that this danger exists even when the smoke is second-hand."