[High prevalence of secondary hyperparathyroidism due to vitamin D insufficiency in Graves' disease].Clin Calcium. 2005 Sep; 15 Suppl 1:68-70; discussion 70.CC
We studied concentrations of serum calcium, intact parathyroid hormone (iPTH), and 25 hydroxyvitamin D (25 [OH] D) in 343 patients with Graves' disease (273 women, 70 men) during one year period. The serum 25 (OH) D levels were 37+/-19 nmol/L and vitamin D deficiency (defined as a serum 25 (OH) D value below 25 nmol/L) was found in 35% of the patients. There was a significant seasonal variation in the 25 (OH) D concentrations, with high values of 51+/-21 nmol/L during the summer term (July-September), and with low values of 26+/-17 nmol/L during the winter term (January-March). The average serum iPTH level was 48+/-26 pg/mL, with 26% (89/343) having values above the normal range. Our results showed high prevalence of secondary hyperparathyroidism in patients with Graves' disease during antithyroid drug therapy and vitamin D and/or calcium supplements are recommended for patients with vitamin D deficiency.