Middle-age male smokers endure the equivalent of an extra ten years of aging on their global cognition and executive function, according to a new study.

Researchers at University College London (UCL; United Kingdom) conducted a cohort study involving 5,099 men and 2,137 women (mean age 56 years) participating in the Whitehall II study to examine the association between smoking history and cognitive decline in the transition from midlife to old age. The assessment included a cognitive test battery composed of memory, vocabulary, executive function (composed of one reasoning and two fluency tests), and a global cognitive score summarizing performance across all five tests. The first cognitive assessment was in 1997-1999, repeated in 2002-2004 and then in 2007-2009. The main outcome measure was the association between smoking history and 10-year cognitive decline.

The results showed faster cognitive and executive function decline among male current smokers, when compared to never smokers. Recent ex-smokers had greater decline in executive function, while the decline in long-term ex-smokers was similar to that among never smokers. The 10-year cognitive decline (in all tests except vocabulary) among the never smokers ranged from a quarter to a third than that of the smokers. When taking into account dropout and death, these differences were 1.2-1.5 times larger. In women, however, cognitive decline did not vary as a function of smoking status. The study was published early online on February 6, 2012, in the Archives of General Psychiatry.

“While we were aware that smoking is a risk factor for respiratory disease, cancer, and cardiovascular disease, this study shows it also has a detrimental effect on cognitive ageing and this is evident as early as 45 years,” said lead author Séverine Sabia, PhD, of the UCL department of epidemiology and public health. “A 50 year old male smoker shows a similar cognitive decline as a 60 year old male never smoker.”

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