MONDAY, Feb. 6, 2012 (HealthDay News) -- Smoking appears to speed declines in memory, thinking, learning and processing information in men, but not in women, new research suggests.
One expert said the findings are just one more reason to quit the habit.
"This study underscores that smoking is bad for your brain, and that mid-life smoking is a modifiable risk factor with an effect size roughly equivalent to 10 years of aging on the rate of [mental] decline," said Dr. Marc Gordon, chief of neurology at Zucker Hillside Hospital in Glen Oaks, N.Y. He was not involved with the research.
The new study was led by Severine Sabia of University College London. She and her colleagues analyzed data collected from nearly 5,100 men and more than 2,100 women who had three assessments of mental functions such as memory, learning and thought-processing over 10 years and six assessments of smoking status over 25 years. The participants were an average of 56 years old at the time of their first assessment.
The investigators found that, for men, smoking was associated with more rapid decline in these brain skills. In addition, a greater decline in all tests was noted among men who continued to smoke during the follow-up period.
But quitting didn't necessarily help right away: Men who kicked the habit in the 10 years before their first assessment were still at risk of more mental decline, particularly in their so-called "executive" functioning, which includes various complex mental processes involved in planning and achieving a particular goal.
However, men who were long-term ex-smokers did not have faster decline, according to the study published in the Feb. 6 online edition of the journal Archives of General Psychiatry.
"Finally, our results show that the association between smoking and cognition [mental skills], particularly at older ages, is likely to be underestimated owing to higher risk of death and dropout among smokers," the study authors pointed out in a journal news release.
It is important to note that while the study uncovered an association between smoking and mental decline in men, it did not prove a cause-and-effect relationship.
Gordon agreed that questions remain on the exact link between smoking and brain health. "The mechanism of how smoking results in increased [mental] decline remains unclear," he said. "In this study, the effect was not explained by cardiovascular disease, hypertension, elevated cholesterol, or impaired lung function."
The researchers found no link between smoking and declines in mental abilities in women. The reasons for this gender difference aren't clear, but the fact that men tend to smoke more cigarettes than women may be one explanation, they suggested.
According to Gordon, the study's sample size might also be a factor. "There was a smaller proportion of women (about 30 percent) in the cohort [and] a higher percentage of women had never smoked," he pointed out.
The American Heart Association outlines the risks of smoking.