aim of studying men's health [12]. A total of 51,529 men in health professions were recruited, and every two years, members of the study receive questionnaires similar to the ones used in NHS. In HPFS, we have collected blood samples from 18,159 participants and cheek cell samples from an additional 13,956 men. The Physicians’ Health Study (PHS) is a randomized primary prevention trial of aspirin and supplements among 29,067 United States physicians followed with annual questionnaires since 1982 [13]. A total of 14,916 men provided a baseline blood sample.
