Introduction
obesity, chronic disease
OBESITY, CHRONIC DISEASE
Vitamin D is an essential micronutrient relevant to numerous biological processes. It is produced endogenously as vitamin DExcess body weight and obesity are consistently characterized by lower 25-OHD blood levels and a higher prevalence of vitamin D insufficiency and deficiency in cross-sectional studies.We hypothesized that, in addition to differences in circulating total 25-OHD levels with vitamin D supplementation, obesity would modify other circulating markers of vitamin D bioavailability and activity. Of total vitamin D in circulation, 85% to 90% is bound to a vitamin D–binding protein (VDBP). Bioavailable 25-OHD (BioD) is the remaining 10% to 15% vitamin D fraction in circulation that is not bound to VDBP; BioD is primarily bound to albumin. Free vitamin D (FVD) levels represent less than 1% of total vitamin D. Identifying subgroups with suboptimal response to supplementation underscores the potential role for future precision prevention strategies to tailor dosing and maximize the effectiveness of vitamin D supplementation for chronic disease prevention. We investigated this aim in a post hoc analysis of the randomized VITAL, with repeated measures at baseline and 2 years for total vitamin D, FVD, BioD, VDBP, albumin, parathyroid hormone (PTH), and calcium.