initial visit, confirmatory testing is required.
Diabetes diagnosis outside of
D2d is validated by laboratory testing
as part of D2d or, if the participants
started diabetes-specific medication,
by review of medical records by the
clinical outcomes committee, whose
members are independent of the D2d
Research Group (Fig. 3).
Results of the screening and baseline
glycemic measures are provided to participants
and their health-care providers.
After randomization, numeric
results of glycemic tests are not provided
to sites, participants, or healthcare
providers until a participant meets
the primary end point of diabetes. At
that point, glycemic results are shared
with the site, participant, and healthcare
providers, and the participant is referred
to his or her physician for further
care in relation to diabetes; however,
the participant continues in the study,
taking the study pills without unmasking
and returning for all scheduled visits (for
assessment of other outcomes). Secondary
outcomes include safety and tolerability
of vitamin D supplementation;
variation of response to vitamin D supplementation
among subgroups defined
by key baseline characteristics; variability
of response to vitamin D supplementation
by adherence based on pill counts
and by achieved 25OHD concentration;
effect of vitamin D supplementation on
hemoglobin A1c, FPG, and 2hPG as continuous
variables, insulin resistance and
secretion (indices derived from the
OGTT), systolic and diastolic blood pressure
and blood 25OHD concentration;
and identification of phenotypic, including
seasonal and geographic, characteristics
associated with variation in achieved
blood 25OHD concentration.
Statistical Analyses and Sample Size
Calculations
In accordance with the intention-totreat
principle, the primary analysis
will compare treatment groups defined
by the randomization procedure and
will include all events observed during
the study irrespective of adherence to
assigned treatment. When participants
withdraw (i.e., go off study), follow-up
will be censored at the date of the last
visit. Exploratory per-protocol analyses
and analyses in subgroups defined by
level of adherence to study treatment
will be undertaken as well but are not