Years of smoking may cloud the brain as well as the air, according to a new study.

Researchers found long-term cigarette smoking was associated with diminished thinking skills as well as lower IQ among a group of alcoholic and nonalcoholic men.

Previous studies have shown that long-term alcoholism dims thinking skills and eventually lowers IQ, and researchers say 50 percent-80 percent of alcoholics are also smokers.

If the findings of this study are confirmed by others, researchers say they suggest that smoking may account for a portion of the mind-numbing effects normally associated with alcoholism.

"We can't say that we've found a cause-and-effect relationship between smoking and decreased thinking ability," says researcher Jennifer Glass, PhD, a research assistant professor of psychiatry at the University of Michigan, in a news release. "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."

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Smoking May Dim Thinking Skills

The study was designed to look at alcoholism’s long-term effect on the brain and thinking skills in a group of 172 alcoholic and nonalcoholic men over a period of about 15 years.

The results, published in the Alcohol and Drug Dependence, concurred with previous findings that alcoholism caused thinking problems and lowered IQ, but they also showed that smoking had a similarly negative effect on the brain.

Researchers found the effect of smoking on memory, problem-solving, and IQ was most pronounced among those men who had smoked for many years. The negative effect of smoking on the brain remained significant in alcoholic men after alcohol and drug use were taken into account.

"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," says researcher Robert Zucker, PhD, professor of psychology at the University of Michigan, in the release. "This is consistent with other findings that people with cardiovascular disease and lung disease tend to have reduced neurocognitive function."

Researchers say the findings should prompt alcoholism researchers to re-examine their data for any impact from smoking because smoking is not usually taken into account in studies of alcoholism’s effects on the brain, despite the fact that many alcoholics smoke.

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By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Glass, J. Drug and Alcohol Dependence, Sept. 15, 2005; advance online publication. News release, University of Michigan Health System.