To identify a healthy population, participants with diagnoses of cardiovascular disease or cancer at baseline were excluded. After further exclusion of participants with missing information on smoking at baseline, data from 43,816 participants in HPFS (1986–2008), 116,566 in NHS (1976–2008) and 92,651 in NHS II (1989–2007) were available for analysis. The study protocol was approved by the institutional review boards of Brigham and Women's Hospital and Harvard School of Public Health.
