Protective effects of 1-α-hydroxyvitamin D₃ on residual β-cell function in patients with adult-onset latent autoimmune diabetes (LADA)

Background: Previous in vitro and in vivo studies have demonstrated that vitamin D could prevent pancreatic β-cell destruction and reduce the incidence of autoimmune diabetes. In children with type 1 diabetes, vitamin D treatment produces moderate protective effects on residual β-cell function and has proven to be safe. Therefore, we hypothesized that vitamin D might have protective effects on β-cell function in patients with latent autoimmune diabetes in adults (LADA), a form of slowly progressive autoimmune type 1 diabetes. Methods: Thirty-five patients with LADA were randomly assigned to receive subcutaneous insulin alone (n = 18) or insulin plus 1-α- hydroxyvitamin D3 (1-α(OH)D3; 0.5 μg per day) (n = 17) for 1 year. Plasma C-peptide levels in fasting state (FCP) and 2 h after 75-g glucose load (PCP) were measured every 6 months with radioimmunoassay. Results: Both FCP and PCP levels stayed steady in the insulin plus 1-α(OH)D3 group, while FCP decreased in insulin-alone group (P = 0.006) during the 12-month intervention. Seventy percent of patients treated with 1-α(OH)D3 maintained or increased their FCP concentrations after 1 year of treatment, while only 22% of patients treated with insulin alone maintained stable FCP levels (P < 0.01). Further analysis on LADA subgroups with different durations of diabetes demonstrated that islet β-cell function was better preserved (as reflected by significantly higher FCP and PCP levels) in the 1-α(OH)D3 plus insulin group only in patients with diabetes duration no longer than 1 year. No severe side effects were observed in any group. Conclusion: Our data suggest that 1-alpha(OH)D3 plus insulin therapy can preserve pancreatic β-cell function in patients with LADA.