Evaluating the effect of vitamin D supplementation on serum levels of 25-hydroxy vitamin D, 1,25-dihydroxy vitamin D, parathyroid hormone and renin–angiotensin–aldosterone system: a systematic review and meta-analysis of clinical trials

BACKGROUND: Vitamin D, one of the most essential micronutrients, is crucial in various health outcomes. However, previous studies showed conflicting results and uncertainty about vitamin D supplementation's optimal dosage and duration. In this study, we aimed to evaluate the vitamin D supplements efficiency on serum levels of 25-hydroxy vitamin D (25(OH)D), 1,25-dihdroxy vitamin D (1,25(OH)2D), parathyroid hormone (PTH) and renin–angiotensin–aldosterone system (RAAS) in adults. METHODS: A systematic analysis of eligible and relevant randomized-controlled trials (RCT) published before April 2023 assessing the effect of vitamin D supplementations applied. The studies were identified by searching several databases, including Pubmed, Scopus, Web of Science, ProQuest, and Cochrane Register of controlled trials. RESULTS: Five eligible RCTs with 346 participants in the intervention and 352 participants in the control group were assessed in our project. According to the results, there was a substantial change in 25(OH)D (SMD: 2.2, I(2): 92.3, 95% Confidence Interval (CI): 1.38–3.02, P-value: 0.048) and 1,25(OH)2D (SMD:1.23, I(2): 86.3, 95% CI: 0.01- 2.44, P-value < 0.010) affected by vitamin D intervention. Regarding Parathyroid hormone (PTH), however, vitamin D intervention showed a remarkable decrease (SMD: -0.75, I(2): 82.4, 95% CI: (-1.3)—(-0.18), P-value < 0.010). Moreover, sensitivity analysis showed significant publication bias in terms of 25(OH)D. CONCLUSION: Vitamin D supplements significantly increase the serum levels of 25(OH)D and 1,25(OH)2D and decrease PTH levels. While some studies reported decreasing effect of vitamin D supplements on RAAS activity, some reported no changes.