Smoking and Cognitive Decline Among Middle-Aged Men and Women: The Doetinchem Cohort Study

Astrid C. J. Nooyens, MSc; Boukje M. van Gelder, PhD; W.M. Monique Verschuren, PhD

Disclosures

Am J Public Health. 2008;98(12):2244-2250. 

In This Article

Abstract and Introduction

Abstract

Objectives: We studied the effect of smoking on cognitive decline over a 5-year period at middle age (43 to 70 years).
Methods: In the Doetinchem Cohort Study, 1964 men and women in the Netherlands were examined for cognitive function at baseline and 5 years later. The association between smoking status and memory function, speed of cognitive processes, cognitive flexibility, and global cognitive function were assessed.
Results: At baseline, smokers scored lower than never smokers in global cognitive function, speed, and flexibility. At 5-year follow-up, decline among smokers was 1.9 times greater for memory function, 2.4 times greater for cognitive flexibility, and 1.7 times greater for global cognitive function than among never smokers. Among ever smokers, the declines in all cognitive domains were larger with increasing number of pack-years smoked.
Conclusions: Interventions to prevent or stop people from smoking may postpone cognitive decline in middle-aged persons.

Introduction

With the aging of populations in Western societies, the number of people with dementia, one of the most common neurodegenerative disorders, is expected to rise. Decline in cognitive function is one of the major symptoms of dementia. A preclinical or subclinical phase of reduced cognitive function precedes the appearance of diagnosed Alzheimer's disease by at least 10 years.[1] Persons with mild cognitive impairment progress to dementia or Alzheimer's disease at a rate of 10% to 15% per year. Among these persons, those with a faster rate of cognitive decline have a greater chance of developing dementia.[2]

The pathophysiology of dementia is complex and still largely unclear, and there is no treatment that can stop its progress. Because age and genetics cannot be controlled, it is important to examine risk factors for dementia that can be modified. Lifestyle factors (e.g., smoking) are suitable for interventions.

Most studies have been done with elderly participants (aged 65 years and older). Based on the results of several case–control studies among the elderly, smoking has been reported to have a protective effect on the risk of Alzheimer's disease.[3,4] Other studies were inconclusive about the effect of smoking on cognitive function.[5] More recently, prospective studies have shown that smoking increases the risk of cognitive decline and dementia among the elderly,[6,7,8,9] which was confirmed in a recent meta-analysis by Anstey et al.[10]

In studies of the effects of smoking among the elderly, there can be a selection bias caused by differential mortality among smokers.[11] Furthermore, to postpone or prevent cognitive decline and, eventually, dementia at old age, intervention is required by middle age. In addition, to determine cause and effect, it is essential to study associations between potential determinants and cognitive decline in a longitudinal design. Very few studies have examined the relationship between smoking and cognitive function at middle age.[12,13,14] The only longitudinal study conducted showed that heavy smoking is associated with memory decline.[14]

In 2002, we showed in a cross-sectional study that smoking was associated with lower cognitive function in several cognitive domains among middle-aged men and women.[13] We now report the effect of smoking on cognitive decline over a 5-year period among men and women in the same age group.

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