Associations between vitamin D2 and metabolic indices in institutionalized older adults -a cross-sectional study.

Reduced sun exposure and inadequate dietary intake are major contributors to vitamin D deficiency in older adults. While vitamin D3 is well studied, the metabolic role of vitamin D2 (VD2) remains underexplored. This study investigated associations between serum VD2 and selected metabolic indices in an institutionalized elderly population. In our study 95 older adults (mean age: 63±14 years) were assessed for dietary intake, body composition, 25(OH)D, VD2, vitamin D receptor (VDR) protein, and hormones regulating energy homeostasis. Food intake was evaluated <i>via</i> a questionnaire and analyzed using dedicated software. Participants were overweight, with excessive caloric intake and insufficient protein and vitamin D consumption. Serum 25(OH)D concentrations indicated vitamin D deficiency (17.6±23.9 ng/mL). Serum VD2 showed significant positive correlations with insulin (r=0.87, <i>p</i><0.001), adiponectin (r=0.41, <i>p</i><0.001), leptin (r=0.22, <i>p</i>=0.034), and VDR (r=0.37, <i>p</i><0.001), and a negative correlation with non-HDL cholesterol in women (r=-0.33, <i>p</i>=0.042). Principal component analysis (PCA) was used to reduce data dimensionality. In the full sample, two components were extracted. Multiple regression including age, gender, medication use, and PCA components showed that PC1 (with high loadings for insulin, leptin, adiponectin) and gender were significant predictors of VD2 levels, together explaining 41.6% of the variance. Among participants with HOMA-IR <2.5, indicating preserved insulin sensitivity, a single principal component - characterized by insulin, adiponectin, and leptin - explained 69.4% of the variance in VD2 levels. In conclusion, significant associations between VD2 and energy-regulating hormones suggest a potential physiological role for VD2 in metabolic homeostasis, particularly among individuals with preserved insulin sensitivity. The observed inverse relationship with non-HDL cholesterol in women additionally points to a possible involvement of VD2 in lipid metabolism. These findings underscore the importance of further investigation into the role of VD2 in endocrine and metabolic health among aging individuals.