Don't take passive smoking lightly or you could end up with impared thinking, sleeplessness, depression and clouded consciousness, according to the latest research.This is the first large-scale study to conclude that exposure to passive smoking could also lead to dementia and other neurological problems in adults.

The research was led by David Llewellyn of University of Cambridge and his associates, which used saliva samples from nearly 5,000 non-smoking adults aged over 50 years.

By measuring levels of cotinine (a by-product of nicotine) in their saliva and taking a detailed smoking history, the researchers were able to assess levels of exposure to passive smoke.

A range of neuro-psychological tests were used to assess aspects of brain function such as verbal memory (recalling words immediately and after a delay), numerical calculations, time orientation, and verbal fluency.

These results were added to provide a global score for cognitive function, and those whose scores were in the lowest 10 percent were subsequently identified as suffering from cognitive impairment.They concluded that exposure to second-hand smoke may be linked to an increased chance of developing cognitive impairment, including dementia, said a Cambridge release.

The authors proposed a number of possible explanations for why exposure to second-hand smoke may increase the odds of dementia, including an increased risk of heart disease and stroke which are known to increase the risk of cognitive impairment and dementia. The research was published in the British Medical Journal Friday.