The Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) are prospective cohort investigations among 121,700 female U.S. registered nurses aged 30–55 years at baseline in 1976 (NHS) and 51,529 U.S. male health professionals, aged 40–75 years at baseline in 1986 (HPFS). Information about health and disease is assessed biennially and information about diet every four years by self-administered questionnaires.[25], [26] Between 1989 and 1990, a blood sample was requested from all participants of the NHS, and returned from 32,826 women. Similarly, between 1993 and 1995, a blood sample was returned from 18,225 men in the HPFS. Participants who provided blood samples were similar in terms of cardiovascular risk factors to those who did not, albeit somewhat younger. In the NHS, among women without cardiovascular disease or cancer prior to blood draw, we identified 249 women with incident nonfatal myocardial infarction (MI) or fatal coronary heart disease (CHD) over 8 years of follow-up. In the HPFS, we similarly identified 266 men with incident nonfatal MI or fatal CHD over 6 years of follow-up. Using risk-set sampling which selects
