People who inhale second-hand smoke on a regular basis may be more likely to need a private dementia care home in later life, new research in the British Medical Journal suggests.
Scientists tested saliva samples from nearly 5,000 non-smoking over-50s to measure a compound called cotinine, which is a by-product of nicotine.
They also conducted neuropsychological tests to assess the participants' brain function and cognitive decline.
Analysis revealed that a high level of second-hand exposure was associated with a 44 per cent increase in individuals' risk of cognitive impairment.
Lead researcher Dr David Llewellyn, from the University of Cambridge, commented: "We have conducted the first study to examine the association between second-hand smoke exposure and cognitive impairment in elderly non-smokers.
"Our results suggest that inhaling other people's smoke may damage the brain, impair cognitive functions such as memory and make dementia more likely."
Around 700,000 people in the UK have a form of dementia and this is expected to soar to 1.7 million people by 2051.