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

Vitamin D supplementation may influence oxidative stress, but evidence in populations following specific dietary patterns is limited.

In this non-randomized, two-group exploratory study, 50 Orthodox nuns received vitamin D supplementation (2000 IU/day orally) for 16 weeks, whereas 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-were measured at baseline and post-intervention.

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 Orthodox 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.

In conclusion, sixteen weeks of vitamin D supplementation in women adhering to Orthodox fasting produced no consistent improvements in oxidative stress markers. While a small reduction in TBARS was observed, this effect was modest and appeared indirect, being more closely associated with decreases in body weight and fat mass than with vitamin D status itself. Taken together, our findings indicate an overall neutral impact of vitamin D on redox balance, suggesting that any antioxidant benefit is likely secondary to metabolic or adiposity-related changes.