From Medscape Medical News > Psychiatry
Smoking Linked to Cognitive Decline in Middle-Aged Men
Joe Barber Jr, PhD
June 21, 2012 — Middle-aged male smokers are more likely to have a faster decline in aspects of cognitive function, new research shows.
Results from the Whitehall II study, a large cohort of British Civil Service employees, show that compared with never smokers, middle-aged men experienced more rapid cognitive decline in global cognition and executive function. However, in exsmokers who had quit for at least 10 years, there was no adverse impact on cognitive decline.
“There is increasing evidence that smoking is a risk factor for dementia. However, its impact on cognitive decline and particularly on cognitive decline in early old age remained unclear,” lead author Séverine Sabia, PhD, University College London, in England, and colleagues write.
The study is published in the June issue of Archives of General Psychiatry.
The authors obtained data from the Whitehall II study, which is based on British Civil Service employees. Among the 7236 individuals (5099 men, 2137 women) who had complete data on smoking history and other covariates, significantly greater 10-year declines were observed among male current smokers than among male never smokers in global cognition (mean difference in decline, -.09; 95% confidence interval [CI], -.15 to -.03; P < .05) and executive function (mean difference in decline, -.11; 95% CI, -.17 to -.05; P < .05) at phase 5.
Conversely, no significant differences were observed in these variables between female current smokers and female never smokers (global cognition: mean difference in decline, .03; 95% CI, -.05 to .12; executive function: mean difference in decline, .03; 95% CI, -.06 to .12).
The Whitehall II study collected data on cigarette smoking in phases 1 (1985 to 1988), 3 (1991 to 1994), 5 (1997 to 1999), 7 (2002 to 2004), and 9 (2007 to 2009), and cognitive function was investigated using a series of 5 tests. The authors excluded data for participants who died or dropped out of the study before phase 5 or failed to complete at least 1 cognitive assessment over 10 years from the analysis.
After 10 years of follow-up (phase 9), among men, persistent smokers had significantly greater deficits in global cognition (mean difference in decline, -.12; 95% CI, -.19 to -.04; P < .05), memory (mean difference in decline, -.15; 95% CI, -.29 to -.01; P < .05), and executive function (mean difference in decline, -.11; 95% CI, -.20 to -.03; P < .05). No evidence of an association between smoking and cognitive decline was observed among women.
The limitations of the study included the lack of representativeness of the cohort of the general population; the self-report nature of the study, which likely lead to underreporting; the inability to ascertain cases of dementia; the dependence of the cognitive tests on writing speed; and the use of assumptions that cannot be tested using observed data.
“Several reasons could explain the fact that we did not find an effect in women,” Dr. Sabia notes. “First, our sample was composed of less women than men (2000 women vs 5000 men), reducing the probability to find an association in women. Furthermore, it is possible that smoking behavior is differently associated with other behavior in men and women.”
The authors have disclosed no relevant financial relationships.