Circulating levels of vitamin D metabolites in patients with hyperinsulinaemia.

Circulating levels of vitamin D metabolites were studied in hyperinsulinaemic patients with insulinoma or insulin autoimmune syndrome. Plasma ionized calcium, parathyroid hormone, and 24,25-dihydroxyvitamin D (24,25(OH)2D) levels were not statistically different from controls, but the 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D) levels were significantly decreased in these patients, compared to controls (P less than 0.01 and P less than 0.05, respectively). However, the ratio of 24,25(OH)2D to 25(OH)D and that of 1,25(OH)2D to 25(OH)D in hyperinsulinaemic patients were significantly higher (P less than 0.01) than in controls. These results suggest that there may be alterations of vitamin D metabolism in the endogenous hyperinsulinaemic state.