Researchers in several European countries studied smoking habits and the change in cognitive function in a group of 9,209 non-demented men and women aged 65 and older over an average of 2.3 years. Cognitive function was screened with a series of questions and tests called the Mini-Mental State Examination (MMSE).
Among those who never smoked (41 percent), the MMSE score declined .03 points per year. The score for current smokers (22 percent) declined .16 points per year, about five times more. Former smokers (37 percent) dropped .06 points per year.
"On the individual level, a small difference in MMSE score has little meaning," said study author Alewijn Ott, MD, of Erasmus Medical Center in Rotterdam, the Netherlands. "On the group level, rates of change are more informative and show that smoking has an impact on cognitive function in the elderly."
Greater cognitive decline occurred with higher cigarette pack-year exposure, a calculation involving the number of years someone has smoked and the reported average daily number of cigarettes. This was significant mainly for the former smokers and not the current smokers, perhaps due to lower numbers of current smokers in the study and greater measurement error in this group, Ott noted.
On the MMSE, 30 points is the maximum score meaning highest cognitive function. Twenty-four points or less may imply an early stage of dementia, Ott said. The average MMSE score of the study group was 27.4 at baseline and 27.2 after the follow-up period.
A family history of dementia did not influence the greater decline in MMSE score in smokers.
Smoking could affect cognitive function through various mechanisms. Chronic tobacco use causes atherosclerosis and hypertension. This, and other effects of smoking, increase the risk of stroke and small, "silent" brain infarctions, Ott noted.
"More in-depth studies are needed to verify if these or other factors are responsible for greater cognitive decline in smokers," said Ott.
The data for this group of 9,209 came from studies conducted in Denmark, France, the Netherlands and the United Kingdom, who are part of the EURODEM Incidence Research Group. The European Community Concerted Action Epidemiology of Dementia (EURODEM) is a collaboration of centers.
The study was supported by the Directorate General XII of the European Commission.
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