Evidence Level
Vitamin D plays a significant role in immune function and overall health. A participant-level meta-analysis by Martineau et al. (2017) involving 25 RCTs and 11,321 participants demonstrated that vitamin D supplementation significantly reduced the risk of acute respiratory infections, particularly benefiting individuals with low baseline levels. Aranow (2011) highlighted the immunological mechanisms, noting that vitamin D receptors are present on various immune cells, including B cells, T cells, monocytes, and dendritic cells, and that vitamin D induces cathelicidin, an antimicrobial peptide with direct bactericidal and antiviral activity.
Recent studies have explored additional benefits of vitamin D. Tamblyn et al. (2022) conducted a systematic review and meta-analysis of 10 studies involving 7,663 participants, finding that vitamin D deficiency (<50 nmol/L) increases the risk of miscarriage (OR=1.94). Abboud (2022) reported that vitamin D supplementation significantly improved sleep quality compared to placebo in a meta-analysis of three RCTs, providing moderate evidence for its role in enhancing sleep outcomes.
However, not all studies have shown consistent benefits. Yeung et al. (2023) reviewed 128 RCTs involving 11,270 adults with chronic kidney disease and found no significant effect of vitamin D therapy on all-cause mortality compared to placebo. Additionally, Formisano et al. (2023) noted that while psoriasis patients had lower serum 25(OH)D levels than controls, oral vitamin D supplementation did not improve PASI scores in RCTs.
Overall, the evidence underscores the importance of adequate vitamin D levels for immune function and certain health outcomes, though its effects may vary across different conditions.