Enhanced suppression of 1,25(OH)2D3 and intact parathyroid hormone in Graves' disease as compared to toxic nodular goiter.

1.25(OH)2D3, 25OHD3, and intact parathyroid hormone, as well as various parameters of calcium-phosphorus metabolism were measured in 38 patients with Graves' disease (GD) and in 24 patients with toxic nodular goiter (TNG). Plasma 1.25(OH)2D3 levels were lower in GD patients (82 +/- 29 pmol/liter) than in those with TNG (155 +/- 32 pmol/liter) (P less than 0.0005). The mean value of 1.25(OH)2D3 in 45 controls was intermediate between the two groups of patients (140 +/- 41) and the difference was statistically significant. GD patients before and after treatment had higher alkaline phosphatase (P less than 0.05), lower intact parathyroid hormone (PTH) (P less than 0.05), and lower 1.25(OH)2D3 levels (P less than 0.0005 in the hyperthyroid and P less than 0.01 in the euthyroid state) than TNG patients. We conclude that increased skeletal calcium resorption is due to elevated levels of T3 causing suppression of 1.25(OH)2D3 production and of PTH levels in both groups of patients albeit of different degrees. Furthermore, we postulate that the profound suppression of 1.25(OH)2D3 in GD is secondary to an immune-mediated phenomenon.