Age at starting smoking and number of cigarettes smoked.

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 day 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.(ABSTRACT TRUNCATED AT 250 WORDS)