Middle-aged men who smoke suffered more rapid cognitive decline than peers who have never smoked or who have been ex-smokers for at least 10 years, researchers reported Monday in the Archives of General Psychiatry.
Smoking is known to be a risk factor for dementia in the aged, but the extent to which it is a risk factor for cognitive problems earlier in life is less-well understood, wrote the team.
Led by Severine Sabia of University College London’s Department of Epidemiology and Public Health, the researchers looked at data collected from 5,099 men and 2,137 women. The subjects were employees of the British Civil Service who had participated in the Whitehall II study, which launched in 1985 and which conducted its ninth phase from 2007 to 2009.
To assess the relationship between subjects’ smoking history and their level of cognitive decline, Sabia and her colleagues reviewed six self-reported assessments of smoking status collected over a period of 25 years, and three assessments of cognitive function collected over a period of 10 years. The cognitive tests were administered when participants were 44-69 years old, 50-74 years old and 55-80 years old.
They found that male smokers exhibited faster mental decline than non-smokers -- and the decline was more pronounced the more cigarettes a subject smoked.
“The effect size associated with smoking is similar to that associated with 10 years of age,” they wrote.
Smokers who had quit at least 10 years before the first assessment did not show a significant speed-up in cognitive decline. Neither did women -- perhaps, the authors wrote, because the men in the study smoked more than the women did. They also hypothesized that it could be because smoking was associated with other risk factors in men, such as greater alcohol consumption.
The team wrote that it was not sure of the mechanism behind smokers’ rapid mental decline, suggesting that it could stem from vascular or lung damage.
“It is increasingly recognized that age-related cognitive pathologies such as dementia result from long-term processes, perhaps beginning as long as 20 to 30 years before the clinical diagnosis of dementia. Our study illustrates the importance of examining risk factors for cognitive decline much earlier in the life course,” the coauthors concluded.