Smoking is associated with a decline in reasoning ability and with memory deficit as early as in middle age, according to a study of more than 5,000 people.
People who quit smoking before they reach middle age, however, show little of this adverse effect on cognition, according to Severine Sabia of the National Institute for Health and Medical Research at Paul Brousse Hospital in Villejuif, France, and her associates.
Previous studies concluded that smoking is a risk factor for dementia in older adults; it is thought to act primarily through its adverse effect on the vasculature. In this study, the investigators used data from the Whitehall II study to examine the relation of smoking to earlier cognitive impairment, before the onset of dementia.
“Cognition in midlife is clinically relevant because research suggests that individuals with mild cognitive impairment progress to clinically diagnosed dementia at an accelerated rate,” Ms. Sabia and her associates noted (Arch. Intern. Med. 2008;168:1165–73).
The Whitehall II study was a longitudinal assessment of socioeconomic factors and health among more than 10,000 British civil servants aged 35–55 years at baseline in 1985–1988.
The subjects were followed at intervals through 2002–2004.
For this study, data were analyzed for a subset of 5,388 participants who underwent evaluation of cognitive function and who furnished a complete smoking history. Short-term verbal memory, inductive reasoning, vocabulary, and verbal fluency were assessed using a battery of standardized tests.
The study participants were categorized as never smokers (2,543 subjects), current smokers (815 subjects), long-term exsmokers (1,519 subjects who had quit before 1985), and recent exsmokers (511 subjects who quit smoking after the study began).
Current smokers were more likely to show deficits, as well as a decline over time in the performance of memory, reasoning, and verbal fluency tasks, than were never smokers.
However, the investigators found no dose-response relationship between the number of pack-years of smoking and cognitive decline.