Vitamin D Metabolism in Hyperthyroidism

Abstract

The serum concentrations of 25-hydroxycholecalciferol (25 OH D3), 24,25-dihydroxycholecalciferol [24,25(OH)-2D3] and 1,25-dihydroxycholecalciferol [1,25(OH)2D3] were measured in twenty-one patients with untreated hyperthyroidism. Compared with control subjects, 25 OH D3 concentrations were not altered, 24,25(OH)2D3 concentrations were increased, although not significantly and 1,25(OH)2D3 concentrations were decreased (P = 0.01). Following oral carbimazole therapy, 24,25(OH)2D3 concentrations fell (P less than 0.01), 1,25(OH)2D3 concentrations increased (P less than 0.01) and 25 OH D3 concentrations were unchanged. The altered 1,25(OH)2D3 and 24,25(OH)2D3 concentrations found in hyperthyroidism are probably due to the effects of thyroid hormone on bone and mineral metabolism. Increased serum calcium and phosphate concentrations with secondary hypoparathyroidism result in stimulation of the renal 24-hydroxylase and suppression of the 1-hydroxylase enzymes. In addition, serum 24,25(OH)2D3 concentrations were significantly correlated with serum triiodothyronine levels (T3) (r = 0.66, P less than 0.002) before treatment. This may indicate a direct stimulatory effect of T3 on 24-hydroxylase activity. No relationship was found between serum 1,25(OH)2D3 concentrations before therapy and serum T3.

Hormones and the Intestinal Absorption of Calcium and Phosphate in Man

“…With radiocalcium and radiophosphate tests, we have observed that the absorbed dose of 45Ca in patients with untreated hyperthyroid ism was significantly lower than in normal subjects (n = 20, 45Ca fx 0.105 ± 0.035, p < 0.001 ), whereas the absorbed dose of 32P was slightly but not significantly lower than in normal subjects (n = 18, 32P fx 0.170 ± 0.047). The cause of the diminished Ca ab sorption in hyperthyroidism remains uncer tain: recent data indicate that circulating l,25-(OH)2D3 levels are decreased [29]. But from our data, we cannot exclude that the rapid gastric emptying and the increased rate of small intestinal transit, frequently associ ated with hyperthyroidism, could play a role in Ca malabsorption in these patients.…”

High Prevalence of Vitamin D Deficiency in Japanese Female Patients with Graves' Disease.

“…Several studies have reported a high prevalence of vitamin D deficiency in selected populations including nursing home residents and persons over age 65 [8,9] . There have been few studies, however, of seasonal variations [10][11][12][13][14] in vitamin D levels in Graves' patients.…”

“…There were no significant differences in serum calcium, corrected calcium, alkaline phosphatase concentrations, or thyroid function between the four seasonal periods for either female or male patients (data not shown). In all of these studies, serum 25(OH)D levels were measured in untreated patients, but one study by MacFarlane et al [13] showed serum 25(OH)D levels to be unchanged following oral carbimazole therapy.…”

Relationship between gestational transient thyrotoxicosis and vitamin D

“…In addition, the current literature shows that vit D is deficient in both hypo-and hyperthyroidism. However, these results are contradictory and inconclusive (19)(20)(21)(22) Vitamin D deficiency is a widespread disorder seen in approximately 30% to 50% of the adult population (25,26). It is generally due to a lack of adequate sunlight exposure and/or nutritional vit D intake (27).…”