Secondhand Smoke Bad for Brain?
Study Links Secondhand Smoke Exposure to Cognitive Impairment
Feb. 12, 2009 -- People who are exposed to secondhand smoke may be more
likely than their peers to have cognitive impairment, a new study shows.
The study, published in the advance online edition of BMJ (formerly
called the British Medical Journal), doesn't prove that secondhand smoke
exposure causes cognitive impairment. But it does show that cognitive
impairment was more common among nonsmokers and former smokers with high
levels of cotinine, a nicotine-related chemical, in their saliva samples.
The study included 4,809 adults 50 and older in England. They provided
saliva samples and took various tests of mental skills, including memory and
attention, between 1998 and 2002. Participants were considered
cognitively impaired if their overall test score was in the bottom 10% of the
Never smokers with the highest salivary levels of cotinine were 70% more
likely to be cognitively impaired than never smokers with the lowest salivary
levels of cotinine. Former smokers with the highest salivary cotinine levels
were 32% more likely to have cognitive impairment than former smokers with the
lowest salivary cotinine levels.
The findings held despite other factors, including participants' age, sex,
education, diabetes, high blood pressure, and heart disease. But the
researchers -- who included David Llewellyn, PhD, of England's University of
Cambridge -- note that the study also has some limits.
For instance, the researchers couldn't control for every possible factor
that may have influenced the results. Also, participants weren't followed over
time, so it's not clear which came first -- cognitive impairment or secondhand
smoke exposure. And although cognitive impairment can take decades to develop,
cotinine doesn't linger in the body very long, so it's not a marker of
long-term exposure to secondhand smoke.
"This study raises the strong possibility that secondhand smoke causes
cognitive decline, but further research is needed to establish a causal
effect," Mark Eisner, MD, MPH, an associate professor of medicine at the
University of California, San Francisco, writes in an editorial published with