Secondhand Smoke Linked to Adult Cognitive Impairment

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By John Gever, Senior Editor, MedPage Today
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco . Earn CME/CE credit
for reading medical news

CAMBRIDGE, England, Passive smoking can damage the brain of those 50 and older, researchers here said

Nonsmokers with the heaviest secondhand smoke exposure were at a 44% higher risk of scoring in the bottom 10% on cognitive testing, compared with those with the lowest level of passive smoking (P=0.02), reported David J. Llewellyn, Ph.D., of the University of Cambridge, and colleagues online in BMJ.


This result occurred after controlling for such potential confounding factors as age, sex, ethnicity, alcohol consumption, socioeconomic status, education, physical activity, body weight, medical history, depressive symptoms, and ex-smoker status.


"This analysis is to our knowledge the first to examine the relation between exposure to secondhand smoke and cognitive impairment in a large heterogeneous population-based sample," according to the researchers. Other studies have connected secondhand smoke exposure to impaired cognition in children and adolescents.


They said the findings were of "major public health significance" and called for additional, prospective studies to confirm and extend them.


The study involved 4,809 self-described nonsmokers at least 50 years old who participated in both of two large national health surveys and gave saliva samples.


One of the surveys, the English Longitudinal Study of Aging, included detailed cognitive testing that evaluated immediate and delayed verbal memory, attention and processing speed, prospective memory, numerical abilities, and semantic fluency.


Those in the bottom 10% of the combined cognitive score were considered impaired.


Cotinine, a nicotine metabolite that signals recent exposure to tobacco smoke, was measured in the saliva samples. Participants with cotinine levels higher than 14 ng/mL were excluded to ensure the study population did not contain clandestine tobacco users.


After adjusting for the potential confounding factors, the researchers found that people in the highest quartile of cotinine level -- 0.8 to 13.5 ng/mL -- had an odds ratio of 1.44 of being impaired (95% CI 1.07 to 1.94), relative to those in the lowest quartile.


Participants in the second and third quartiles showed small and statistically insignificant risks of cognitive impairment.


The relation between passive smoking exposure and cognitive impairment was strongest in participants who never smoked.


Never-smokers in the highest cotinine quartile had an odds ratio for impairment of 1.70 (95% CI 1.03 to 2.80). For ex-smokers with the heaviest smoke exposure, the odds ratio was 1.32 (95% CI 0.92 to 1.91).


Dr. Llewellyn and colleagues said.......more later