Vitamin D Deficiency in Newly Diagnosed Type 1 Diabetes Mellitus

Abstract

Background: Type 1 diabetes mellitus (T1DM) is a multifactorial autoimmune disease in which environmental and nutritional factors interact with genetic susceptibility to drive β-cell estruction. Vitamin D has attracted growing interest for its immunomodulatory effects, ediated through vitamin D receptors expressed on immune cells and pancreatic β-cells.

Objective: This narrative review synthesizes current evidence on the role of vitamin D deficiency in the onset and progression of newly diagnosed T1DM, integrating mechanistic, pidemiological, and clinical data.

Methods: A narrative review of basic science, epidemiological, observational, and interventional studies addressing vitamin D metabolism, immunoregulation, and its relationship to T1DM.

Key Findings: Vitamin D modulates T-helper cell balance (suppressing Th1/Th17, promoting Th2/Treg), reduces pro-inflammatory cytokines, inhibits β-cell ferroptosis and apoptosis, and supports regulatory T-cell function. Vitamin D deficiency is highly prevalent at T1DM diagnosis (approximately 45–56% in pediatric cohorts) and shows seasonal and age-related variation. Birth-cohort studies suggest supplementation during infancy may reduce T1DM risk, while interventional trials in newly diagnosed patients show inconsistent results, with the strongest signals for short-term preservation of C-peptide/β-cell function and enhanced Treg activity using cholecalciferol (vitamin D₃). No universally accepted dosing guidelines currently exist.

Conclusion: Vitamin D deficiency is common and mechanistically plausible as a contributor to T1DM pathogenesis, but current evidence supports correlation rather than proven causation. Routine screening in newly diagnosed pediatric T1DM patients is reasonable given the high deficiency prevalence, while large, standardized randomized controlled trials are needed to establish optimal dosing, timing, and clinical benefit.