By Kara Gavin
Originally published by UMHS Public Relations October 17, 2005

Smokers often say that smoking a cigarette helps them concentrate and feel more alert, but years of tobacco use may have the opposite effect, dimming the speed and accuracy of a person’s thinking ability and bringing down his IQ, according to a study by University of Michigan Medical Center (U-M) researchers.

The association between long-term smoking and diminished mental proficiency in 172 alcoholic and non-alcoholic men was a surprising discovery from a study that set out to examine alcoholism’s long-term effect on the brain and thinking skills.

While the researchers confirmed previous findings that alcoholism is associated with thinking problems and lower IQ, their analysis also revealed that long-term smoking is, too. The effect on memory, problem-solving and IQ was most pronounced among those who had smoked for years. Among the alcoholic men, smoking was associated with diminished thinking ability even after accounting for alcohol and drug use.

The findings, released online before publication by the journal Drug and Alcohol Dependence, were made by a team from the U-M Addiction Research Center, or UMARC, and colleagues at the VA Ann Arbor Healthcare System and Michigan State University.

Lead author Jennifer Glass, a research assistant professor in the Department of Psychiatry, cautions that the results need to be duplicated by other studies before conclusions are made about smoking’s effect on the brain, or before the findings can be considered relevant to women.

But, she says, the results should prompt alcoholism researchers to re-examine their data for any impact from smoking—a factor that usually is not taken into account in studies of alcoholism’s effects on the brain, despite the fact that 50 percent to 80 percent of alcoholics smoke. The U-M-led team, meanwhile, is launching a study that will examine the issue in adolescents and plans to test the 172 men again soon.

“We can’t say that we’ve found a cause-and-effect relationship between smoking and decreased thinking ability, or neurocognitive proficiency,” Glass says. “But we hope our findings of an association will lead to further examination of this important issue. Perhaps it will help give smokers one more reason to quit, and encourage quitting smoking among those who are also trying to control their drinking.”

Many alcoholism-recovery programs don’t emphasize quitting smoking, even though smoking can be a social and possibly chemical cue associated with alcohol consumption.

Glass notes that her team’s paper is being published at the same time as one from a team at the University of California, San Francisco, in which brain scans showed that alcoholics who smoke have lower brain volume than alcoholics who don’t smoke.

Taken together with previous epidemiological studies, the two papers feed a growing body of evidence for a link between long-term smoking and thinking ability, says Robert Zucker, professor of psychology in the departments of Psychiatry and Psychology, and director of UMARC. Zucker is senior author on the new paper led by Glass.

“The exact mechanism for smoking’s impact on the brain’s higher functions is still unclear, but may involve both neurochemical effects and damage to the blood vessels that supply the brain,” Zucker says. “This is consistent with other findings that people with cardiovascular disease and lung disease tend to have reduced neurocognitive function.”

The data for the paper by Glass come from an ongoing longitudinal project that uses interviews and standardized research questionnaires to look at mental and physical health issues in families, measured every three years.

The study, which has run for more than 15 years and recently was funded for another five, is supported by the National Institute of Alcoholism and Alcohol Abuse, part of the National Institutes of Health (NIH)

The new work that will explore these relationships in youth is being funded by the National Institute on Drug Abuse, also part of the NIH.