ANN ARBOR, Mich. -- Smokers often say that smoking a cigarette helpsthem concentrate and feel more alert. But years of tobacco use may havethe opposite effect, dimming the speed and accuracy of a person'sthinking ability and bringing down their IQ, according to a new studyled by University of Michigan researchers.

The association between long-term smoking and diminished mentalproficiency in 172 alcoholic and non-alcoholic men was a surprisingfinding from a study that set out to examine alcoholism's long-termeffect on the brain and thinking skills.

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

The findings are the first to suggest a direct relationship betweensmoking and neurocognitive function among men with alcoholism. And, theresults suggest that smoking is associated with diminished thinkingability even among men without alcohol problems.

The new findings, released online before publication by thejournal Drug and Alcohol Dependence, were made by a team from the U-MMedical School's Addiction Research Center, or UMARC, and theircolleagues at the VA Ann Arbor Healthcare System and Michigan StateUniversity.

Lead author Jennifer Glass, Ph.D., a research assistant professor inthe U-M Department of Psychiatry, cautions that the findings need to beduplicated by other studies before any conclusions are made aboutsmoking's effect on the brain, or before the findings can be consideredrelevant to women.

But, she says, the findings should prompt alcoholism researchers tore-examine their data for any impact from smoking -- a factor that isnot usually taken into account in studies of alcoholism's effects onthe brain, despite the fact that 50 percent to 80 percent of alcoholicssmoke. Meanwhile, the U-M-led team is launching a study that willexamine the issue in adolescents, and plans to test the 172 men againsoon.

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"We can't say that we've found a cause-and-effect relationshipbetween smoking and decreased thinking ability, or neurocognitiveproficiency," says Glass. "But we hope our findings of an associationwill lead to further examination of this important issue. Perhaps itwill help give smokers one more reason to quit, and encourage quittingsmoking 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, coincidentally,at the same time as a paper from a team at the University ofCalifornia, San Francisco, in which brain scans showed that alcoholicswho smoke have lower brain volume than alcoholics who don't smoke, andthat cognitive function decreases with brain volume among non-smokingalcoholics, but not smoking alcoholics.

Taken together with previous epidemiological studies, the two newpapers feed a growing body of evidence for a link between long-termsmoking and thinking ability, says Robert Zucker, Ph.D., professor ofPsychology in the U-M Departments of Psychiatry and Psychology, anddirector of the UMARC. Zucker is senior author on the new paper led byGlass.

"The exact mechanism for smoking's impact on the brain's higherfunctions is still unclear, but may involve both neurochemical effectsand damage to the blood vessels that supply the brain," Zucker says."This is consistent with other findings that people with cardiovasculardisease and lung disease tend to have reduced neurocognitive function."

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The data for the new paper by Glass, Zucker and their colleagues at U-Mand Michigan State University, come from an ongoing longitudinal, orlong-term, project that uses interviews and standardized researchquestionnaires to look at mental and physical health issues infamilies, measured every three years.

The study, which has run for more than fifteen years and recently wasfunded for another five, is supported by the National Institute ofAlcoholism and Alcohol Abuse, part of the National Institutes ofHealth. The new work that will explore these relationships further inyouth is being funded by the National Institute on Drug Abuse, also apart of the NIH.

In their ninth year in the study, participants completed the MicroCogAssessment of Cognitive Function, a well-established standard batteryof tests that assess short-term memory, immediate and delayed storyrecall, verbal analogies, mathematical reasoning and visual-spatialprocessing.

Scores for each test, and a global proficiency score, are based on thespeed and accuracy of a person's responses, adjusted for age andeducation level. The participants also took a short form of thestandard IQ test, and their scores were adjusted for age.

Forty of the men had clinically diagnosable alcoholism at the time ofthe test, though none had been drinking within an hour of the tests.Twenty-four of these men also were smokers. The study also included 63men who had had alcoholism earlier in life, 29 of whom smoked; and 69men who had never been alcoholic, 13 of whom smoked. All smokers wereallowed to smoke at will during the testing session, so none were in anicotine-deprived state when they took the neurocognitive tests.

Glass and her colleagues analyzed the participants' scores using twostandard measures of long-term drinking and smoking behavior: lifetimealcohol problem severity, or LAPS, and pack-years, a measure that takesinto account the number of packs of cigarettes a person smoked each dayand the number of years they smoked that much.

Across the board, both smoking and drinking showed an effect: Higherpack-years and LAPS scores were both significantly associated withlower global cognitive proficiency scores and IQ.

When the researchers limited the analysis to those participants who hadever had a diagnosis of alcoholism during their lifetime, they stillfound a significant association between LAPS scores and IQ, and betweenpack-years and both IQ and overall cognitive proficiency. In fact, theimpact of heavy lifetime smoking history was greater than the effect oflifetime drinking history.

This finding, Glass says, means that alcoholism researchers who haveconsistently found evidence of cognitive deficits among alcoholics --but who have not taken smoking into account in their analysis -- mayactually be seeing a combined effect of smoking and alcohol consumptionamong alcoholic study participants who smoke. Further analyses of thesedata, with smoking separated out as a variable just as hard drug use isoften separated, is needed, she says.

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Glass, who also holds positions in the U-M's Institute for SocialResearch and Chronic Pain & Fatigue Research Center, co-authoredthe paper with Zucker, and with Kenneth Adams, Ph.D., a professor ofpsychology in psychiatry at U-M and chief of the psychology service atVAAAHCS; Maria Wong, Anne Buu, Jennifer Jester and Leon Puttler ofUMARC; and Joel Nigg and Hiram Fitzgerald of MSU. Reference: Drug andAlcohol Dependence, online at doi:10.1016/j.drugalcdep.2005.08.013.