Vitamin D3 supplementation in women practicing orthodox religious and intermittent fasting: A controlled study with formulation-specific effects

Background

Vitamin D deficiency is prevalent among monastic Orthodox populations, likely due to their sartorial habits and religious fasting rules. Data on supplementation in similar populations are lacking, including responses in restoring vitamin D sufficiency and to specific formulations of vitamin D supplements. This controlled study evaluated the efficacy of a daily oral vitamin D regimen, using oil-based drops and tablets, in restoring vitamin D status in a population of Orthodox nuns from Northern Greece, as well as assessing potential formulation-specific effects in the context of vitamin D supplementation.

Methods

A total of 41 Orthodox nuns practicing intermittent fasting received a daily dose of 2.500 IU vitamin D3 in either oil-based drops or tablets for 16 weeks and were compared to 40 matched controls without supplementation. Serum concentrations of 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH), calcium, and albumin were measured at baseline and after 16 weeks in both groups.

Results

In the supplemented group, mean serum 25(OH)D concentrations increased significantly from 21.44 ± 9.08 ng/mL to 34.27 ± 10.33 ng/mL (p = 0.022), while PTH decreased from 66.18 ± 21.31 pg/mL to 50.71 ± 15.92 pg/mL (p = 0.018). The control group showed no significant changes in either 25(OH)D (23.90 ± 7.11 vs. 26.53 ± 9.14 ng/mL, p = 0.067) or PTH (41.75 ± 15.74 vs. 40.11 ± 13.56 pg/mL, p = 0.415). Multivariate regression—adjusting for baseline 25(OH)D, BMI, and body fat percentage—indicated that the form of supplementation (tablet vs. drops) was not an independent predictor of the change in vitamin D concentrations (β = +2.77, p = 0.456). The only statistically significant predictor was baseline 25(OH)D (β = −0.63, p < 0.001).

Conclusions

A daily regimen of oral vitamin D3, administered as either drops or tablets, is effective in significantly improving vitamin D status and reducing PTH concentrations in women adhering to intermittent fasting religious practices. These findings support targeted supplementation strategies in at-risk fasting populations, particularly those with vitamin D deficiency, regardless of the form of oral supplementation.