Given its anticipated diverse population
(;40% nonwhites with a wide age
and BMI range) selected without regard
to baseline 25OHD concentration, its
long-term follow-up, and its careful assessment
of safety, D2d is expected
to contribute important insights into
the heterogeneity of treatment effect
and safety profile of vitamin D
supplementation. Importantly, the
study will serve as the backbone for
ancillary analyses to meet additional
vitamin D–related research needs and
for various other studies to harness
the considerable potential of the
parent study for obtaining new
knowledge beyond its primary goals
(www.d2dstudy.org/ancillarystudies).