Age at starting smoking and number of cigarettes smoked in Catalonia, Spain

Background. Few studies have investigated the association between age at starting smoking and the average number of cigarettes smoked per day in adulthood. To provide further evidence on this issue, we analyzed data from the Catalan Health Interview Survey (CHIS). Methods. The CHIS was conducted in 1994 on a randomly selected sample (N = 15,000) of the population of Catalonia, Spain. A total of 4,897 current or exsmokers (3,276 males and 1,621 females) were included for analysis. Age-standardized proportions of subjects smoking <15, 15-24, and greater than or equal to 25 cigarettes/day, age-standardized mean number of cigarettes smoked per day, and multivariate odds ratios (OR) of being a heavy smoker (greater than or equal to 25 cigarettes/day) according to age at starting smoking (<15, 15-17, 18-19, greater than or equal to 20 years) were computed. Results. Men who started smoking before the age of 15 smoked on average 5.5 cigarettes more than those who started at age 19 or over. Women who started smoking early in life smoked, on average, 6.8 cigarettes/day more than women who started later. The proportion of smokers of <15 cigarettes/day was higher among subjects who started smoking later. Both for males and for females, the OR of being a heavy smoker significantly increased with decreasing age at starting smoking (OR = 2.4 for males and 4.5 for females who started at age <15 versus greater than or equal to 20 years). The level of education did not modify the relationship in males, whereas the association with age at starting was only apparent for more educated women. Conclusions. This study confirms that age at starting smoking is inversely and strongly associated to the number of cigarettes smoked per day. Thus, actions aimed at the prevention or delay of smoking onset among adolescents would have an important beneficial effect.