Multivariable-Adjusted Mean or Geometric Mean Vitamin D–Related Biomarkers at Baseline and 2 Years’ Follow-up, by Randomized Treatment Assignment and BMI
WEST, TYPE 2 DIABETES
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); 25-OHD, 25-hydroxyvitamin D; PTH, parathyroid hormone; SEM, standard error of the mean; VDBP, vitamin D binding protein.SI conversion: To convert albumin to grams per liter, multiply by 10; calcium to millimoles per liter, multiply by 0.25; 25-OHD to nanomoles per liter, multiply by 2.496; PTH to nanograms per liter, multiply by 1.Values were adjusted for baseline factors: age (continuous), sex (male, female), prevalence of type 2 diabetes, preintervention vitamin D supplement use, smoking status (never, past, current, not reported), total physical activity (above, below median = 16.6 MET-h/week), race and ethnicity (Asian or Pacific Islander, Black, Native American or Alaska Native, non-Black Hispanic, non-Hispanic White, other/unknown, not reported), geographic region (West, South, Midwest, Northeast), season of blood draw (winter, spring, summer, fall), and in-person Clinical and Translational Science Center subgroup participation. Mean treatment effects were additionally adjusted for baseline biomarker concentrations. Tests for interaction of treatment effect by baseline BMI category were additionally adjusted for baseline biomarker concentrations and baseline biomarker × BMI interaction.Sample sizes included for each biomarker: total 25-OHD, n = 2635; 25-OHD3, n = 2632; free vitamin D, n = 964; bioavailable vitamin D, n = 963; VDBP, n = 964; albumin, n = 2732; PTH, n = 2730; calcium, n = 1997.We repeated the above models of treatment effect heterogeneity by baseline WC categories for the subset of 964 Clinical and Translational Science Center participants with in-person measurements (eTable 2 in In a sensitivity analysis, we evaluated treatment effect heterogeneity by baseline BMI, restricted to 377 (14.6%) participants with low vitamin D levels at baseline (total 25-OHD <20.0 ng/mL) (eTable 3 in 