Background Vitamin D deficiency is highly prevalent in populations following intermittent or religious fasting, particularly Orthodox nuns with limited sun exposure and dietary restrictions. Vitamin D may modulate adipokines and inflammatory markers, but clinical evidence remains inconsistent. Objective To investigate the effects of vitamin D supplementation on interleukin-6 (IL-6) and leptin concentrations in Orthodox nuns compared with non-supplemented controls. Methods In this controlled, non-randomized trial, 33 Orthodox nuns received oral vitamin D 3 supplementation (2,500 IU/day) for 16 weeks, while 42 age-matched women following Orthodox intermittent fasting served as controls. Anthropometric indices and serum concentrations of 25-hydroxyvitamin D 25(OH)D, IL-6, leptin, parathyroid hormone, insulin, and C-reactive protein were measured at baseline and follow-up. Results At baseline, serum 25(OH)D concentrations were lower in the supplementation group compared with controls (23.4 ± 10.1 vs . 27.7 ± 11.2 ng/mL, p = 0.043). After 16 weeks, 25(OH)D increased significantly in the supplementation group (23.4 ± 10.1 vs . 33.9 ± 11.0 ng/mL, p 0.001), with no change in controls (27.7 ± 11.2 vs . 28.5 ± 12.2 ng/mL, p = 0.941). Leptin showed a non-significant decrease in the supplementation group (24.4 ± 18.3 vs . 21.9 ± 13.5 ng/mL, p = 0.215), whereas in the controls, it remained unchanged (23.21 ± 14.67 vs . 24.05 ± 13.89 pg/mL, p = 0.365). IL-6 did not change significantly in either group. Exploratory multivariable regression did not reveal significant predictors of leptin changes. Conclusions Vitamin D supplementation effectively corrected deficiency but did not significantly affect leptin or IL-6 concentrations. These results highlight the need for larger and longer studies to further clarify the immunometabolic impact of vitamin D supplementation in women practicing intermittent fasting.
Karras et al. (2025) studied this question.