METHODS
Study Population
Approval for this study was obtained from the University
of Minnesota Institutional Review Board Human Subjects
Committee. Consent for participation was obtained
from all participants and their parents or guardiansParticipant recruitment and study methods have been
described in detail previously (30). Briefly, after blood
pressure screening of 12,043 fifth- to eighth-grade Minneapolis,
MN, public school students, 500 study participants
were randomly selected by strata of sex, race (black
or white), and blood pressure percentiles (one half of
study participants had blood pressure measurements in
the upper 25th percentiles and the other one half of study
participants had blood pressures in the lower 75th percentiles).
Of the 400 youth who enrolled in the main study
about the influence of insulin sensitivity on blood pressure
change, 357 participated at a mean age of 13 years
(range 11 to 15 years) and 304 participated at mean age
15 years (range 13 to 17 years) between February 1996
and January 2000. To evaluate the relations between
flavonoid intake and biomarkers in the current study, the
cohort for this study consisted of 285 participants with
complete data for dietary intake collected at two time
points, average ages 13 and 15 years, and for clinical
measures, fasting blood and overnight urine samples collected
at average age 15 years