Age at Starting Smoking and Number of Cigarettes Smoked BARBARA D'AVANZO, PnD, CARLO LA VECCHIA, MD, AND EVA NEGRI, ScD A cross-sectional analysis of a sample of 3235 males and 2513 females included in a structured framework of case-control studies of various neoplasms conducted in northern Italy assessed the relationship between age at starting smoking and amount of cigarettes smoked per day. Age- standardized proportions of light, moderate, and heavy smokers and mean numbers of cigarettes smoked per clay according to age at starting, together with age- and sex-adjusted odds ratios of being a heavy smoker were computed. Age at starting smoking was strongly associated with the number of cigarettes smoked per day. This relationship was evident in men and women and at younger and elderly ages, although in women the mean numbers of cigarettes smoked was lower than in men, and age at starting was a stronger predictor of subsequent heavy smoking in people younger than 55 years than in the elderly. Among males who had started smoking before age 17, 64% smoked less than 25 cigarettes/d and 37% smoked 25 or more cigarettes; corresponding proportions were 73% and 27% among those who had started at age 30 or later. Age-standardized mean number of cigarettes smoked per day by men who started before age 17 was 23.5, compared to 20.0 for those who started at age 30 or later. Corresponding values for women were 16.8 and 10.5. Compared to those who started smoking at age 30 or later, the odds ratios of smoking more than 25 cigarettes/d for those who started before age 17 were 2.2 (95% confidence interval (CI), 1.6 to 3.0) for men and 5.4 (95% CI, 3.0 to 9.6) for women. The relationship between young age at starting and high number of cigarettes smoked per day further stresses the importance of age at starting smoking on subsequent health consequences. Ann Epidemiol 1994;4:455-459. KEY WORDS: Epidemiology, cross-sectional study, smoking. INTRODUCTION Age at starting smoking is a major determinant of subse- quent risk of tobacco-related disease. Lung cancer mortality at ages 55 to 64 years, for instance, is four to five times higher in subjects who started smoking before age 15 as compared to those who started at age 25 or later, even for subjects who reported comparable numbers of cigarettes smoked per day (1-3). It is less clear whether age at starting smoking is corre- lated to other characteristics of smoking habits. An analysis of a large American case-control investigation suggested that age at starting smoking is inversely related to frequency of smoking; that is, subjects who started earlier tended to smoke more cigarettes later in life (4). Correlates of age at starting smoking may, however, be different in various populations and age groups. To describe the relationship between age at starting smoking and number of cigarettes smoked in an Italian From Istituto di RicercheFarmacologiche "Mario Negri"(B.D., C.L.V., E.N.) and Istituto di Biometria e Statistica Medica, Universita di Milano (C.L.V.), Milano, kaly. Address reprint requests to: Barbara D'Avanzo, PhD, Istituto di Ri- cerche Farmacologiche "MarioNegri,"Via Eritrea 62, 20157Milano, Italy. Received December 6, 1993; revised February 10, 1994. population, we considered data from a series of case-control studies conducted in northern Italy. SUBJECTS AND METHODS Since 1983, we have been conducting a structured series of case-control studies of various neoplasms, based on a network of hospitals including the National Cancer Insti- tute, several university clinics, and the Ospedale Maggiore, grouping the four largest teaching and general hospitals in TABLE 1. Distribution (number [%]) of 5748 smoking subjects according to sex and age group: Milan, kaly, 1983 to 1992 Sex Age group (y) Male Female 29 34 (1.1) 30-34 65 (2.0) 35-39 131 (4.0) 40-44 223 (6.9) 45-49 339 (10.5) 50-54 501 (15.5) 55-59 565 (17.5) 60-64 620 (19.2) >/ 65 757 (23.4) Total 3235 (100.0) 100 (4.0) 123 (4.9) 233 (9.3) 311 (12.4) 338 (13.5) 35O (13.9) 335 (13.3) 334 (13.3) 389 (15.5) 2513 (100.0) © 1994 by Elsevier Science Inc. 1047-2797/94/$07.00