Shared Immunopathogenic Mechanisms in Chronic Spontaneous Urticaria, Vitiligo, and Hashimoto's Thyroiditis: The Role of Oxidative Stress and Vitamin D

Introduction: Chronic spontaneous urticaria (CSU), vitiligo, and Hashimoto's thyroiditis (HT) frequently co-occur in the same patients, suggesting a shared autoimmune pathogenesis. These conditions are increasingly recognized as components of polyautoimmunity, with overlapping clinical, immunological, and pathogenetic features. Among the proposed common mechanisms, vitamin D deficiency and oxidative stress (OS) have emerged as key contributors. We aimed to explore the shared immunopathogenic pathways linking these conditions, with a focus on the interplay between vitamin D status and redox imbalance. Methods: An extensive narrative review of the current literature regarding the associations among CSU, vitiligo, and HT, focusing on the role of vitamin D status, OS, and nitrosative stress, and shared immunological pathways was conducted. Discussion: Vitamin D deficiency was consistently observed across all three conditions and is associated with increased disease activity and poorer clinical outcomes. Several polymorphisms in the vitamin D receptor (VDR) and binding protein genes correlate with disease susceptibility. OS and nitrosative stress markers, such as malondialdehyde (MDA) and nitric oxide (NO) metabolites, are elevated in patients with CSU, vitiligo, and HT, and are linked to tissue-specific immune activation, apoptosis, and loss of self-tolerance. Evidence suggests that vitamin D and antioxidant supplementation may provide clinical benefit. In vitiligo, narrowband ultraviolet B (NB-UVB) phototherapy not only promotes repigmentation through melanocyte stimulation but also reduces ROS production and modulates local immune responses. Conclusions: The coexistence of CSU, vitiligo, and HT reflects a broader systemic autoimmune tendency, with vitamin D deficiency and redox imbalance serving as potential unifying mechanisms. Routine assessment of vitamin D levels and OS parameters may enhance diagnostic precision and inform therapeutic strategies. Antioxidant-based interventions represent promising avenues in the integrated management of autoimmune skin and endocrine disorders.