IQ lowered with long-term smoking
October 11, 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 their IQ,
according to a new study led by University of Michigan researchers.
The association between long-term smoking and diminished mental proficiency in
172 alcoholic and non-alcoholic men was a surprising finding 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 alcohol and drug use were
accounted for.
The findings are the first to suggest a direct relationship between smoking and
neurocognitive function among men with alcoholism. And, the results suggest that
smoking is associated with diminished thinking ability even among men without
alcohol problems.
The new findings, released online before publication by the journal Drug and
Alcohol Dependence, were made by a team from the U-M Medical School's Addiction
Research Center, or UMARC, and their colleagues at the VA Ann Arbor Healthcare
System and Michigan State University.
Lead author Jennifer Glass, Ph.D., a research assistant professor in the U-M
Department of Psychiatry, cautions that the findings need to be duplicated by
other studies before any conclusions are made about smoking's effect on the
brain, or before the findings can be considered relevant to women.
But, she says, the findings should prompt alcoholism researchers to re-examine
their data for any impact from smoking - a factor that is not usually taken into
account in studies of alcoholism's effects on the brain, despite the fact that
50 percent to 80 percent of alcoholics smoke. Meanwhile, the U-M-led team 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,” says Glass.
“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, coincidentally, at the
same time as a paper 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, and that cognitive function decreases with
brain volume among non-smoking alcoholics, but not smoking alcoholics.
Taken together with previous epidemiological studies, the two new papers feed a
growing body of evidence for a link between long-term smoking and thinking
ability, says Robert Zucker, Ph.D., professor of Psychology in the U-M
Departments of Psychiatry and Psychology, and director of the 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 new paper by Glass, Zucker and their colleagues at U-M and
Michigan State University, come from an ongoing longitudinal, or long-term,
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 fifteen 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. The new work that will explore
these relationships further in youth is being funded by the National Institute
on Drug Abuse, also a part of the NIH.
In their ninth year in the study, participants completed the MicroCog Assessment
of Cognitive Function, a well-established standard battery of tests that assess
short-term memory, immediate and delayed story recall, verbal analogies,
mathematical reasoning and visual-spatial processing.
Scores for each test, and a global proficiency score, are based on the speed and
accuracy of a person's responses, adjusted for age and education level. The
participants also took a short form of the standard IQ test, and their scores
were adjusted for age.
Forty of the men had clinically diagnosable alcoholism at the time of the test,
though none had been drinking within an hour of the tests. Twenty-four of these
men also were smokers. The study also included 63 men who had had alcoholism
earlier in life, 29 of whom smoked; and 69 men who had never been alcoholic, 13
of whom smoked. All smokers were allowed to smoke at will during the testing
session, so none were in a nicotine-deprived state when they took the
neurocognitive tests.
Glass and her colleagues analyzed the participants' scores using two standard
measures of long-term drinking and smoking behavior: lifetime alcohol problem
severity, or LAPS, and pack-years, a measure that takes into account the number
of packs of cigarettes a person smoked each day and the number of years they
smoked that much.
Across the board, both smoking and drinking showed an effect: Higher pack-years
and LAPS scores were both significantly associated with lower global cognitive
proficiency scores and IQ.
When the researchers limited the analysis to those participants who had ever had
a diagnosis of alcoholism during their lifetime, they still found a significant
association between LAPS scores and IQ, and between pack-years and both IQ and
overall cognitive proficiency. In fact, the impact of heavy lifetime smoking
history was greater than the effect of lifetime drinking history.
This finding, Glass says, means that alcoholism researchers who have
consistently found evidence of cognitive deficits among alcoholics - but who
have not taken smoking into account in their analysis - may actually be seeing a
combined effect of smoking and alcohol consumption among alcoholic study
participants who smoke. Further analyses of these data, with smoking separated
out as a variable just as hard drug use is often separated, is needed, she says.
Glass, who also holds positions in the U-M's Institute for Social Research and
Chronic Pain & Fatigue Research Center, co-authored the paper with Zucker,
and with Kenneth Adams, Ph.D., a professor of psychology in psychiatry at U-M
and chief of the psychology service at VAAAHCS; Maria Wong, Anne Buu, Jennifer
Jester and Leon Puttler of UMARC; and Joel Nigg and Hiram Fitzgerald of MSU.
Reference: Drug and Alcohol Dependence, online at
doi:10.1016/j.drugalcdep.2005.08.013.
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