Purpose: The purpose of this study was to investigate the precise effect of smoking, duration of smoking, and cessation of smoking on the risk of the development of an abdominal aortic aneurysm (AAA).
Methods: A nested case control study was carried out in a population-based screening program for men over the age of 50 years. Smoking data were collected by questionnaire, and serum levels of cotinine were used as an objective measure of nicotine exposure.
Results: Data of 210 cases and 237 control individuals were analyzed. Current smokers were 7.6 times more likely to have an AAA than nonsmokers (95% confidence interval, 3.3%-17.8%). Exsmokers were 3.0 times more likely to have an AAA than nonsmokers (95% confidence interval, 1.4%-6.4%). Duration of smoking was significantly associated with an increased risk of AAA, and there was a clear linear dose response relationship with the duration of smoking; each year of smoking increased the relative risk of AAA by 4% (95% confidence interval, 2%-5%). In contrast, the effect of the amount smoked disappeared when an adjustment was made for the duration of smoking. After the cessation of smoking, there was a very slow decline in the risk of the occurrence of an AAA. Smoking was associated with a higher relative risk of a small aneurysm than a large aneurysm. Serum cotinine levels were higher in men with a small aneurysm than in men with a large aneurysm. Cotinine levels were similar in expanding aneurysms and stable aneurysms.
Conclusion: The duration of exposure rather than the level of exposure appears to determine the risk of the development of an AAA in men older than 50 years. The slow decline of risk after the cessation of smoking and the higher relative risk for small compared with large aneurysms suggest that smoking is an initiating event for the condition.