Effect of Vitamin D Supplementation on Oxidative Stress Biomarkers in Women Following Religious or Intermittent Fasting Patterns

Background: Vitamin D supplementation may influence oxidative stress, but evidence in populations following specific dietary patterns is limited. Methods: In this 16-week intervention, 50 Orthodox nuns, received vitamin D supplementation (2000 IU/day orally) and 50 age-matched women following time-restricted eating (TRE) served as controls receiving no supplementation. Anthropometric parameters, serum 25-hydroxyvitamin D [25(OH)D], and oxidative stress markers — total antioxidant capacity (TAC), glutathione (GSH), and thiobarbituric acid reactive substances (TBARS) — were measured at baseline and post-intervention. Results: At baseline, both groups were comparable in anthropometric and oxidative stress markers, except for serum 25-hydroxyvitamin D [25(OH)D], which was lower in the intervention group. Following supplementation, serum 25(OH)D increased from 15.77±5.21 to 31.24±7.87 ng/mL (p = 0.031) in Οrthodox nuns.No significant changes were observed for TAC (0.93±0.11 to 0.97±0.09, p = 0.081),and GSH (6.01±1.55 to 5.81±1.41, p = 0.069), whereas TBARS decreased significantly (7.32±1.31 to 6.94±1.21, p = 0.041). No significant changes were observed in controls under TRE. Changes (Δ) in all variables represented the post–pre difference over the 16-week period.Pearson correlations showed no significant associations between Δ25(OH)D and ΔTAC (r = −0.244, p = 0.346), ΔGSH (r = 0.110, p = 0.675), or ΔTBARS (r = −0.116, p = 0.657). In multivariable regression adjusted for age, weight, body fat percentage, and baseline 25(OH)D, Δ25(OH)D was not an independent predictor of oxidative stress marker changes; however, weight (β = 0.08, p = 0.011) and body fat percentage (β = −0.13, p = 0.014) were associated with reductions in TBARS. Conclusions: Sixteen weeks of vitamin D supplementation in nuns adhering to Orthodox Christian fasting increased serum 25(OH)D concentrations and had neutral effects on oxidative stress markers. TBARS improvements could be attributed more closely linked to adiposity reductions than to vitamin D changes per se. Keywords: Vitamin D, oxidative stress, TAC, GSH, TBARS, fasting, women, supplementation