(WebMD) Smoking is bad for the brain, especially for male smokers. Men who smoke tend to have a more rapid mental decline than men who do not smoke, a new study shows. But the findings did not reveal a similar link between smoking and mental decline in female smokers.

Although the exact reason for the sex difference is unclear, one possibility is that women tend to smoke fewer cigarettes a day than men do and for fewer years. Other lifestyle habits, such as male smokers drinking more alcohol, may also account for some differences seen.

In the study, published in the Archives of General Psychiatry, scientists analyzed data from nearly 6,000 men and more than 2,100 women who were British civil servants. To evaluate their thinking abilities, participants were given their first mental assessment at midlife, an average age of 56.

The assessment included five tests of memory, vocabulary, and reasoning (verbal and math) skills. Participants were retested two more times (every five years) over a decade.

To determine volunteers' smoking habits over a 25-year period, researchers looked at their then-current smoking status and past history, including whether they had quit or relapsed.

Faster mental decline was seen in middle-age men who currently smoked than men who never did.

Smoking and Brain Health

Men who were recent ex-smokers had, on average, greater declines in "executive function," a term for more complex thinking skills, than men who never smoked.

But there was good news for people who had laid off cigarettes for at least a decade: Men who were long-term ex smokers did not have greater mental decline than men who never took up tobacco. Scientists suspect the negative effects of smoking on memory and thinking skills might wear off about 10 years after quitting.

It's not surprising that smoking is linked with faster rates of mental decline. Smoking is a risk factor for dementia, and it also increases a person's chances for heart and lung disease, two health problems associated with memory difficulties.

Researchers suspect that other studies may underestimate the impact of smoking on the brain health of older adults because of higher death rates and dropout rates among smokers. So this research looked at middle-aged smokers because the brain changes that can influence memory problems later in life can begin 20 to 30 years earlier.

"Our study illustrates the importance of examining risk factors for [mental] decline much earlier in the life course," the researchers write.

While these findings occurred in white-collar civil service workers, it's not known if similar results would be found in blue-collar workers, the unemployed, or the general population.

By Cari Nierenberg Reviewed by Laura J. Martin, MD

SOURCES:Sabia, S. Archives of General Psychiatry, published online Feb. 6, 2012.News release, Archives of General Psychiatry.