In her study, "cigarette smoking was negatively related to IQ and thinking," she said.

This finding may seem counterintuitive, since many smokers attest to feeling more alert and focused after smoking. Indeed, research shows that improved mental functioning is one of the immediate effects of nicotine exposure. Chronic smoking, however, is known to have the opposite effect.

Studies show that up to 87 percent of alcoholics smoke cigarettes, compared to less than 30 percent of the general United States population. Yet, few studies have looked into cigarette smoking as a factor that might explain the cognitive deficits reported among alcoholics.

To investigate that association, Glass and her colleagues examined brain function among 172 men from the same community, including 103 men who abused alcohol.

The team found that men with higher scores on the lifetime alcohol problems scale (LAPS) and those who reported a higher number of pack-years of smoking (i.e. packs of cigarettes smoked per day times number of years) both had lower IQ scores and lower scores on a test of global proficiency.

The proficiency test took into account the speed and accuracy with which the men were able to perform on a battery of tests including those that measured short-term memory, verbal reasoning and mathematical reasoning.

Upon further investigation, the researchers found that smoking predicted poorer global proficiency even more strongly than alcoholism did. Their findings were published online before publication in Drug and Alcohol Dependence.

Smoking also appeared to be independently associated with weaker verbal and visual-spatial reasoning, the study indicates. Thus, though smoking did not account for all of the decreased neurocognitive functioning observed among the alcohol abusers, it did seem to account for some of the effects, the report indicates.

The reason for the observed associations is unknown, and the researchers did not investigate the "cause and effect story," Glass said, but she speculated that the diminished cognitive ability among smokers may be partly due to some mechanism involving a restricted flow of blood and oxygen to the brain.

Based on the current report, Glass said, "if you need another reason to quit smoking, it's a good potential one to add to the list."

SOURCE: Drug and Alcohol Dependence, 2005