Smokers face a speedier decline in several measures of cognitive function by middle age compared with their non-smoking peers, new research shows.

"Our results indicate that giving up smoking at any age may prevent further smoking-induced cognitive decline," W. M. Monique Verschuren and colleagues from the National Institute for Public Health and the Environment in Bilthoven, the Netherlands, conclude.

There is currently no treatment that will halt the progress of dementia, so identifying ways to help prevent mental decline is crucial, Dr Verschuren and her team note in the American Journal of Public Health. Such preventive steps would have to be taken by the time a person reaches middle age, they add.

To investigate whether smoking might represent a modifiable risk factor for dementia, the researchers followed 1,964 men and women 43- to 70-years old for five years.

Previously, Dr Verschuren and her team had found that the 21.3 per cent of study participants who smoked had lower scores on overall cognitive function and the speed and flexibility of their mental processes than did non-smokers.

In the current study, conducted five years later, the researchers found that memory declined 1.9 times faster in the smokers than in the never-smokers. Declines in cognitive flexibility and global cognitive function were also 2.4 and 1.7 times faster, respectively, in the smokers than in those who never smoked. The more cigarettes a person had smoked during their lives, the steeper was their decline in cognitive function.

Cognitive decline rates for ex-smokers and recent quitters fell between those of the current smokers and the never-smokers, although the differences didn’t reach statistical significance.

Preventing people from starting to smoke, as well as encouraging those who do smoke to quit, no matter what their age, could help people preserve their mental function as they age, the researchers conclude.

Source: American Journal of Public Health, December 2008.