The association between smoking and cognitive function (thinking, learning and memory) has been discussed extensively in recent years. The consensus has been that smoking negatively impacts brain function. However, evaluating this effect in older persons is problematic because old smokers frequently die or don't return for follow-up assessments. One way to avoid some of these problems in clinical study design is to explore the association between smoking and cognitive function before dementia develops.

The link between mild cognitive impairment and dementia is well established. Therefore, it is logical to determine whether there is an association between smoking  and cognitive impairment in midlife. Evidence of a link at younger ages would bolster the contention that smoking is involved in the production of cognitive decline.

Data in a recent study were drawn from 10,308 civil servants in the UK who were followed for an average of 17 years. The relationship between smoking history and multiple domains of cognition was investigated sequentially in middle-aged individuals aged 35-55 at baseline. They included memory, reasoning, vocabulary, and semantic and phonemic fluency.

Compared to those who had never smoked, middle-aged smokers experienced memory deficits and declines in reasoning abilities. Compared with smokers, long-term ex-smokers were less likely to have cognitive problems in memory, vocabulary and verbal fluency. The study also documented that those who gave up smoking in midlife manifested improvements in other health related behaviors such as diet and activity.

These results are significant because individuals with cognitive impairment in midlife due to smoking may progress to dementia at a more rapid rate.