Baseline characteristics of the Nurses' Health Study cohort*.

*Dietary intake and other characteristics at baseline questionnaire in 1980 (mean value, unless otherwise indicated).ΨAll values have been directly standardized according to the age distribution of the cohort.†Pack-years were calculated for former and current smokers only.‡The body-mass index is the weight in kilograms divided by the square of the height in meters.§METS are metabolic equivalents. This was calculated based on the frequency of physical activities (such as jogging) in 1986.