SMOKING IS associated with an increased risk of poor memory and a decline in reasoning ability in middle age, research published today suggests.
The results of the study are considered important because individuals with cognitive impairment in midlife may progress to dementia at a faster rate.
Severine Sabia and her colleagues from the Institut National de la Santé et de la Recherche Médicale, Villejuif, France and the Department of Epidemiology and Public Health, University College London, analysed data from 10,300 civil servants who participated in the Whitehall II Study.
The major study recruited London-based civil servants aged 35-55 between the years 1985 and 1988 and since then has periodically tested them for a wide range of health indicators.
For this study, some 5,400 participants completed tests of memory, reasoning, vocabulary and verbal fluency between 1997 and 1999, while just over 4,600 were re-tested five years later.
During the first round of cognitive testing, those who smoked were more likely to be in the lowest performing group for memory and reasoning compared with those who had never smoked.
There was good news for those who were former smokers at the beginning of the study. They were 30 per cent less likely than smokers to have poor vocabulary and low verbal fluency scores. And those who stopped smoking during the study were more likely to drink less alcohol, be physically active and to eat more fruit and vegetables.
Writing in the latest issue of Archives of Internal Medicine, the authors say the study has a number of key findings.
"First, smoking in middle age is associated with memory deficit and a decline in reasoning abilities. Second, long-term ex smokers are less likely to have cognitive deficits in memory, vocabulary and verbal fluency. Third, giving up smoking in midlife is accompanied by improvement in other health behaviours."
However, the researchers caution that, although the study was a large and prospective one, the data are from white-collar civil servants and cannot be assumed to apply to the general population.
"During the past 20 years, public health messages about smoking have led to changes in smoking behaviour," Ms Sabia and her colleagues note. "Public health messages on smoking should continue to target smokers of all ages."
Last year, research combining the results of a number of key studies (a meta analysis) concluded that smoking is a risk factor for dementia.
While this study confirms a risk link between smoking and poor memory and reasoning ability, there is insufficient evidence to allow conclusions to be made about an association between smoking and specific cognitive tasks.
A link between smoking and poorer cognition is most likely a reflection of the effect smoking has on atherosclerosis, the "furring up" of arteries in the brain and other parts of the body.
Commenting on the results, a spokeswoman for Ash Ireland, the anti-smoking lobby group, said: "This article illustrates yet another good reason to stop smoking and that it is never too late to do so."