Smoking is increasingly recognized as a risk factor for dementia in the elderly and the number of dementia cases worldwide, estimated at 36 million in 2010, is on the rise and is projected to double every 20 years, the researchers wrote in their study background.
Severine Sabia, Ph.D., of University College London, and colleagues used the Whitehall II cohort study, which is based on employees of the British Civil Service.
The authors examined the association between smoking history and cognitive decline in the transition from midlife to old age. Data were obtained from 5,099 men and 2,137 women in the Whitehall II study, with a mean (average) age of 56 years at the first cognitive assessment.
In the current study, researchers analyzed data using six assessments of smoking status over 25 years and three cognitive assessments over 10 years.
The authors note their analysis presents four key findings. They suggest smoking in men is associated with more rapid cognitive decline and those men who continued to smoke over the follow-up experienced greater decline in all cognitive tests.
In addition, men who quit smoking in the 10 years preceding the first cognitive measure were still at risk of greater cognitive decline, especially in executive function (an umbrella term for various complex cognitive processes involved in achieving a particular goal). However, long-term ex-smokers did not show faster cognitive decline.
“Finally, 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,” they noted.
The authors also revealed that their results show no association between smoking and cognitive decline in women, although the underlying reasons remain unclear.
They suggest one explanation for the sex difference they observed might be that men smoke greater quantity of tobacco.
The finding has been published Online First by Archives of General Psychiatry, one of the JAMA/Archives journals.