The study in the Archives of General Psychiatry followed more than 5,000 men and 2,100 women in the British civil service. Research subjects entered the study at an average age of 56 and were followed for up to 25 years.

Researchers at the University College London checked their smoking status six times over that span and ran a series of cognitive tests.

They found that smoking was linked to more rapid declines in mental ability across all cognitive tests among men who smoked when compared to non-smoking men.

"Our results show that the association between smoking and cognition, particularly at older ages, is likely to be underestimated owing to higher risk of death and dropout among smokers," said the study, led by Severine Sabia of University College London.

Men who quit smoking within 10 years of entering the study were still at risk of greater cognitive decline, but long-term ex-smokers did not show the same deterioration levels.

"This study underscores that smoking is bad for your brain," said Marc Gordon, chief of neurology at Zucker Hillside Hospital in Glen Oaks, New York, who was not involved in the study.

"Mid-life smoking is a modifiable risk factor with an effect size roughly equivalent to 10 years of aging on the rate of cognitive decline," he added.

The findings are increasingly relevant to the world's aging population, the study authors said, with some 36 million dementia cases across the globe, a figure that is projected to double every 20 years.

Just why women did not show the same link was unclear, though researchers suggested the smaller sample size and the higher volume of cigarettes smoked by men in comparison to women could be contributing factors.

 

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