In the NHS, we first ascertained the participants' current smoking status(current, past, or those who had never smoked [hereafter referred to as a"never smoker"]) in the initial 1976 questionnaire. For current and past smokers, we assessed the age when smoking began. For current smokers, we asked the average number of cigarettes smoked per day. For past smokers, we asked when they had quit smoking and, on average, how many cigarettes per day they last smoked. In the HPFS, we obtained information on current and past smoking in 1986. Participants were asked whether they had ever smoked 20 packs of cigarettes or more in their lifetime and, if yes, whether they were current or past smokers. For these participants who ever smoked, the mean number of cigarettes smoked per day at each of the 7 age groups (<15, 15-19, 20-29, 30-39, 40-49, 50-59, 60+ years) was assessed. Past smokers were asked how long ago they quit. On subsequent 2-year follow-up questionnaires, we updated participants' smoking status and, for current users, the number of cigarettes smoked. Similarly for covariates, we updated variables such as age, body mass index, and having a diagnosis of hypertension or diabetes mellitus. Alcohol use was updated in 1984, 1986, 1990, and 1994 for women and in 1986, 1990, and 1994 for men. We ascertained participants' ethnicity in 1992 for women and in 1986 for men.