Statistical Analysis
REGRESSION, SKIN, SECONDARY
This analysis is the secondary objective of the trial. The primary objective was focused on lean mass outcomes, with the aim of recruiting a minimum of 46 infants per trial group and up to 74 to account for dropouts.Differences between the trial groups over time in bone outcomes (dual-energy x-ray absorptiometry and biomarkers), vitamin D metabolites, and safety biomarkers (iCa, urinary calcium to creatinine ratio, and urinary phosphate to creatinine ratio) were tested using linear mixed-effects regression models with participant-level random intercepts and slopes for time. We used a first-order autoregressive covariance structure selected based on the correlation matrix and the lowest Akaike information criterion. The variables included group-by-time interaction, time, and participant number. Skin pigmentation, UV-B period and season at birth, infant sex, and socioeconomic and demographic characteristics were explored but not retained in the model. Data were not imputed given that the mixed-effects model used all available data, and data were assumed to be missing at random.A post hoc analysis of covariance tested differences between the trial groups in bone outcomes (WB BMC, LS BMC, and LS BMD) with corresponding baseline values for each dependent variable tested as covariates. In these models, the repeated measures were at 3, 6, and 12 months.All statistical analyses were conducted using SAS University Edition (SAS Institute), and statistical significance was set at 