A new study carried out by the University of Cambridge suggests that breathing in second hand smoke might increase the risk of developing dementia. Second hand smoke is the contaminated air that non-smokers inhale by default when in the company of someone smoking. Dementia is the decline in cognitive function beyond what might be expected from normal aging.

During the study saliva samples of 5,000 non-smokers over 50 were tested for different levels of the chemical cotinine, a by-product of nicotine, which stays in the body for up to 48 hours after inhaling second hand smoke. Those with a high level of cotinine in their saliva were assumed to be exposed to second hand smoke regularly and those with low levels were used as the control group. Both groups were then tested to determine levels or recall and other memory skills.

The group with high exposure to second hand smoke were found to be 44% more likely to show early memory problems, an early indicator for dementia, than the control group.

The link between smoking and dementia has previously been suggested strongly, but this study is the first to link second hand smoke exposure to dementia. It is thought that the heart disease, which is a known smoking risk, could be the common factor, as it is a known risk factor for dementia.

Cambridge University’s Dr D. Llewellyn, who lead the study: “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.”

Dementia is a growing problem in the developed world and it has been an area of fierce scientific effort. It comes on top of the normal or expected reduction of cognitive capability that comes with ageing. Western countries with quality health-care and low birth rates have rapidly aging populations.