Vitamin D deficiency and immune health in polar populations: a systematic review and hypothesis-driven narrative analysis.

Vitamin D is essential for regulating the immune system and preventing disease, yet vitamin D deficiency is common, especially in people living in polar regions. This systematic review examines the interplay between vitamin D levels, immune function, and the unique immunological challenges faced by polar residents. Through a comprehensive review of studies, three main areas were explored: (1) the impact of vitamin D deficiency on immune responses, (2) vitamin D status in polar regions, and (3) widespread immune deficiency in polar populations. Results showed that vitamin D deficiency is associated with increased vulnerability to respiratory infections, autoimmune diseases, and inflammatory diseases, while vitamin D supplementation consistently improved immune markers and downgraded disease severity. People living in polar regions face an increased risk due to limited solar radiation, diet, and environmental stressors, which contribute to increased immunosuppression, altered cytokine profiles, and susceptibility to infections. The summary findings highlight three key factors linking vitamin D deficiency, immune deficiencies, and unique health risks in polar populations. Addressing these deficiencies may be an effective strategy to strengthen immunity and reduce disease burden in these vulnerable groups.