Cigarette smoking is an independent risk factor for cervical intraepithelial neoplasia in young women: a longitudinal study.

Repeated measurements of smoking, cervical human papillomavirus (HPV) status and sexual behaviour were used to measure the risk of high-grade cervical intraepithelial neoplasia (CIN) in relation to changes in smoking and cervical HPV status, and to explore the impact of smoking on the acquisition and duration of incident cervical HPV infection. Included in this longitudinal analysis are 1485 women aged 15-19 years: 1075 were HPV-negative and cytologically normal at recruitment; 410 were HPV-positive, cytologically abnormal or both, at this time. Women re-attended every 6 months, when samples were taken for cytological and virological examination. Current smoking intensity was associated with an increased risk of high-grade CIN, after controlling for cervical HPV status (compared to non-smokers, hazards ratio (HR) for 10 or more cigarettes per day=2.21, 95% confidence interval (CI) 1.19-4.12, p-trend=0.008). In women who were HPV-negative and cytologically normal at recruitment, current smoking was not significantly associated with the risk of acquiring a cervical HPV infection, after controlling for life-time number of partners and age of oldest partner (HR=1.13, 95% CI 0.90-1.41); nor did it prolong the length of time during which HPV could be detected (HR=1.03, 95% CI 0.78-1.34). Current smoking intensity is an independent risk factor for high-grade CIN in young women, after controlling for cervical HPV infection.