Passive Smoking May Well Lead to Cognitive Impairment

A new study has found that exposure to high levels of second-hand smoke could lead to an increased risk of cognitive impairment.

Researchers from the University of Cambridge (UK) conducted a cross sectional stratified random sample analysis study of 4,809 non-smoking adults aged 50 years or more who participated in the 1998, 1999, and 2001 Health Survey for England and the 2002 wave of the English Longitudinal Study of Aging, and who had also provided saliva samples for cotinine (a byproduct of nicotine) assay and a detailed smoking history. The main outcome measures were cognitive impairment, as defined by the lowest 10% of scores on a battery of neuropsychologic tests.

The researchers divided the participants who did not smoke, use nicotine products, or who had salivary cotinine concentrations of 14.1 ng/ml or higher into four equal size groups, on the basis of their cotinine concentrations. The researchers then compared those participants with the lowest fourth of cotinine concentration (0.0-0.1 ng/ml) with the other groups, and found that the odds ratios for cognitive impairment in the second (0.2-0.3 ng/ml), third (0.4-0.7 ng/ml), and highest fourths (0.8-13.5 ng/ml) were 1.08, 1.13, and 1.44, respectively, after adjustment for a wide range of established risk factors for cognitive impairment. A similar pattern of associations was observed for never smokers and former smokers. Based on these results, the researchers recommended that prospective nationally representative study relating biomarkers of exposure to cognitive decline and risk of dementia be undertaken. The study was published in the February 12, 2009, issue of the British Medical Journal (BMJ).

"Our results suggest that inhaling other people's smoke may damage the brain, impair cognitive functions such as memory, and make dementia more likely," said lead author David Llewellyn, Ph.D., of the department of public health and primary care. "Given that passive smoking is also linked to other serious health problems such as heart disease and stroke, smokers should avoid lighting up near nonsmokers."

Cotinine being a metabolite of nicotine; the level of cotinine in the blood is proportionate to the amount of exposure to tobacco smoke, so it is a valuable indicator of tobacco smoke exposure, including passive smoke. There is some research being done on the effects of cotinine on memory and cognition that have suggested, contrary to this study, that cotinine (as well as nicotine) improves memory and prevents neuron death. For this reason it has been studied for effectiveness in treating schizophrenia, Alzheimer's, and Parkinson's diseases.

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