Effect of 1.25-dihydroxycholecalciferol administration on blood glucose and pancreatic islet morphology in mice

Vitamin D and Clinical Outcomes in Dialysis

Most dialysis patients are vitamin D deficient, including deficiencies in both activated vitamin D (1, 25-dihydroxyvitamin D) and the less active 25-hydroxyvitamin D. These and other abnormalities associated with chronic kidney disease (CKD), if they remain untreated, lead to secondary hyperparathyroidism and bone changes, such as osteitis fibrosa cystica. Activated vitamin D has been proven to decrease parathyroid hormone (PTH) levels in dialysis patients and is currently used for this indication. There are multiple other potential "pleotrophic" effects associated with vitamin D therapy. These include associations with lower all-cause and cardiovascular mortality, lower rates of infections and improved glycemic indexes. Meta-analyses of multiple observational studies have shown activated vitamin D therapy to be associated with improved survival. Observational data also suggest fewer infections and better glucose control. There have been no randomized clinical trials powered to evaluate mortality or other clinical outcomes. Small trials of nutritional vitamin D (ergocalciferol and cholecalciferol) showed increases in 25-hydroxyvitamin D levels without hypercalcemia or hyperphosphatemia, even when given in addition to activated vitamin D therapy. While activated vitamin D therapy is associated with improved outcomes, it also leads to higher fibroblast growth factor 23 (FGF-23) levels, which may be detrimental in dialysis patients. Further research is needed to evaluate whether activated or nutritional vitamin D therapy are beneficial in dialysis patients for outcomes other than secondary hyperparathyroidism.

Target cells for 1,25 dihydroxyvitamin D3 in the pancreas

Mature rats raised on a vitamin D deficient diet were injected with tritium labeled, 1,25 dihydroxyvitamin D3. Concentration of radioactivity, which is prevented by pretreatment with unlabeled 1,25 dihydroxyvitamin D3, is found in nuclei of cells that are centrally located in pancreatic islets. The central location of these cells and supportive evidence from the literature suggest that they are B-cells, and that 1,25 dihydroxyvitamin D3 has a direct and genomic action on B-cell functions including insulin secretion.