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. Copyright © 2009 John Wiley & Sons, Ltd.