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Long term smoking contributes to cognitive decline

BMJ 2004; 329 doi: https://doi.org/10.1136/bmj.329.7478.1306 (Published 02 December 2004) Cite this as: BMJ 2004;329:1306
  1. Roger Dobson
  1. Abergavenny

    Researchers have found that among people who had their IQ measured at the age of 11, smokers had the greater cognitive decline by the age of 64. Smokers also had lower psychomotor speeds.

    “We conclude that long term smoking does not produce long term cognitive benefits; to the contrary, smoking makes a small but significant contribution to cognitive decline from age 11 to 64.

    “Current smokers and non-smokers had significantly different mental test scores at age 64. This difference remained after adjustment for childhood IQ,” say the authors of a paper in Addictive Behaviors (2005;30:77-88).

    The authors, from universities at Aberdeen and Edinburgh, who say that some people have claimed that smoking can enhance vigilance, attention and memory, and lower the risk of dementia, set out to investigate whether smoking was a risk factor for relative cognitive decline from age 11 to 64.

    “Of specific interest to the present study was the hypothesis that the contribution of smoking would remain after adjustment of mental scores for childhood intelligence,” say the authors.

    The study was based on about 500 men and women who were all born in 1936 and who had taken part in the same IQ survey in 1947, and who had agreed to be re-examined at the age of about 64 in 2000-2 to measure any decline.

    The results identified smoking as well as childhood IQ, level of education, occupation, and lung function, as significant independent predictors of mental function at age 64.

    “After adjustment for childhood IQ, a positive smoking history was associated with lower performance on tests of psychomotor speed and on a composite score derived from five cognitive tests,” says the report.

    “There were no differences in IQ at age 11 by smoking status, but by age 64, current smokers were performing less well on cognitive tests than non-smokers and former smokers. Psychomotor speed was lower in smokers.”

    The authors added, “The data obtained here suggest that about 5.7% of the variance in cognitive function at age 64 is attributable to the effects of education and occupation after adjustment for IQ at age 11. Thereafter, small but significant negative contributions amounting to no more than about 4% are made by a combination of smoking and impaired lung function acting both together and alone.”

    “Although negative effects on cognition are relatively small in terms of a single individual, these effects are important at the population level. As a lifestyle choice, they are open to modification and thereby to enhancement of retention of cognitive function.”

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