MATERIALS AND METHODSStudy Populati

MATERIALS AND METHODS
Study Population and Data Collection
Data for these analyses were obtained from the NHANES I and
NHEFS. In NHANES I, information was collected from a national
probability sample of the civilian noninstitutionalized population
aged 1 to 74 years from 1971 through 1975. The survey consisted of
a standardized medical examination and questionnaires on various
topics (20–22), such as general medical history, 24-hour dietary
intake recall, and a food frequency interview. Additional data were
gathered from the detailed sample of adults aged 25 to 74 years (N 5
6913). These subjects provided supplemental information about
their medical history and healthcare needs, completed a general
well-being questionnaire, and underwent a more detailed medical
examination. The baseline cohort for the NHEFS consisted of the
14,407 persons aged 25 to 74 years who completed the physical
examinations in the cross-sectional NHANES I survey (70% of the
original cross-sectional sample). Follow-up surveys were conducted
from 1982 through 1984, in 1986 (for those aged 55 years and older
at baseline), and in 1987 and 1992 (23–26). Of the original NHEFS
sample, only 5% were lost to follow-up at all four follow-up surveys.
The analysis presented here included individuals who were 25 to
74 years old at baseline and who underwent the detailed medical
examination (N 5 6913). Only white and black persons were included
because of the small numbers of persons of other races. Of the
6833 individuals eligible for study, 358 were unavailable for follow-
up at all four periods, 116 had a history of stroke at baseline, and
264 had unknown values for one or more variables assessed in the
study. Thus, after all exclusions, 6095 persons were available for
analysis