According to an analysis of data from the Whitehall II study, middle-aged male smokers experienced a faster decline in global cognition and executive function than non-smokers; those who stopped smoking at least ten years previously did not appear to have any increased risk. 

The authors note that smoking is increasingly recognised as a risk factor for dementia in elderly individuals; however the extent to which it increases the risk of cognitive decline remains unclear.  Few studies have investigated the association, especially in non-elderly populations.  The aim of their research was to examine the association between smoking history and decline in multiple domains of cognition, using data from the Whitehall II study, which is based on employees of the British Civil Service.

A total of 10,308 participants were enrolled in the Whitehall II study at baseline (phase 1, 1985-1988), the majority of whom were male (67%).  A clinical examination and self-administered questionnaire were administered at baseline; subsequent follow-up phases involved either a questionnaire alone or both.  Cognitive function testing (using a battery of 5 tests) was introduced at phase 5 (age range 44-69) and repeated in phase 7 (age range 50-74 years).  Data on smoking status were collected at phases 1, 2, 3, 5, 7 and 9; ex-smokers were asked to report the age at which they stopped smoking.   

Data were available for 5,099 men and 2,137 women at the first cognitive assessment (mean age 56 years; range 44-69 years).  The main findings reported were as follows:

• In men, 10-year cognitive decline in all tests except vocabulary among never smokers ranged from a quarter to a third of the baseline standard deviation.

• Faster cognitive decline was observed among current smokers (those still smoking at phase 5) compared with never smokers in men (mean difference in 10-year decline in global cognition of –0.09 [95% CI –0.15 to –0.03] and in executive function of –0.11 [95% CI –0.17 to –0.05]).

• Recent ex-smokers (stopped smoking between phases 1 and 5) had a greater decline in executive function (–0.08 [95% CI, –0.14 to –0.02]), while the decline in long-term ex-smokers (those who stopped before phase 1) was similar to that among never smokers.

• In women, cognitive decline did not vary as a function of smoking status.

The authors comment that public health messages on smoking should continue to target all age groups.