ORIGINAL ARTICLE Serum selenium is low in newly diagnosed Graves’ disease: a population-based study Inge B€ ulow Pedersen*, Nils Knudsen†, Allan Carl  e*, Lutz Schomburg‡, Josef K€ ohrle‡, Torben Jørgensen§¶ , **, Lone Banke Rasmussen††, Lars Ovesen‡‡ and Peter Laurberg* *Department of Endocrinology and Medicine, Aalborg Hospital, Aarhus University Hospital, Aalborg, †Endocrine Unit, Medical Clinic I, Bispebjerg Hospital, Copenhagen, Denmark, ‡Institute for Experimental Endocrinology, Charit  e-Universit€ atsmedizin, Berlin, Germany, §Research Centre for Prevention and Health, Glostrup Hospital, Glostrup, ¶Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, **Faculty of Medicine, Aalborg University, Aalborg, ††Department of Nutrition, National Food Institute, Technical University of Denmark, Søborg and ‡‡Department of Internal Medicine, Slagelse Hospital, Slagelse, Denmark Summary Context Selenium deficiency may play an important role in the initiation and progression of autoimmune thyroid disease. Objective To compare serum selenium (s-Se) values in patients with newly diagnosed autoimmune thyroid disease and controls from the Danish population. Design and settings S-Se was measured in triplicate by a fluo- rimetric method. Participants Patients with newly diagnosed Graves’ disease (GD) (n = 97) or autoimmune overt hypothyroidism (AIH) (n = 96), euthyroid subjects with high serum levels of thyroid peroxidase antibody (TPO-Ab) (TPO-Ab > 1500 U/ml, n = 92) and random controls (n = 830). Main outcome measure Differences in s-Se values. Results S-Se was lower in patients with GD than in controls (mean (SD), GD: 899 lg/l (184); controls: 988 lg/l (197), P < 001). This was confirmed in a multivariate logistic regres- sion model adjusting for age, sex, mineral supplements, smoking, geographical region and time of sampling (P < 001). In a linear model, s-Se was similar in patients with AIH (mean (SD): 984 lg/l (249)) and in controls (P = 086). In the multivariate model however, s-Se was marginally lower in patients with AIH compared to controls (P = 004). There was no significant differ- ence in s-Se between euthyroid participants with high TPO-Ab and random controls (linear: P = 097; multivariate: P = 027). Conclusion Patients with newly diagnosed GD and AIH had significantly lower s-Se compared with random controls. Our observation supports the postulated link between inadequate selenium supply and overt autoimmune thyroid disease, espe- cially GD. (Received 26 November 2012; returned for revision 30 January 2013; finally revised 11 February 2013; accepted 13 February 2013) Introduction Autoimmune thyroid diseases (AITD) are the most common autoimmune disorders in the population. Several studies includ- ing twin studies and epidemiological studies have demonstrated that genetic factors are crucial determinants in the susceptibility to autoimmune disease. However, on a given genetic back- ground, environmental and endogenous factors such as age and previous parities play an important role in the development and maintenance of AITD. Among the many environmental factors that have been suggested to influence the development of thy- roid autoimmunity, the iodine intake may be the most impor- tant. Other suggested risk factors include smoking, oestrogens, drugs, stressful life events, irradiation, infection, allergy, alcohol consumption and selenium deficiency. 1 Selenium is an essential trace mineral and an essential nutri- ent for synthesis of the amino acid selenocysteine which is incorporated into a number of selenoproteins. Until now, 25 human genes encoding selenoproteins are known, of which most are enzymes. 2 The thyroid gland is one of the organs with the highest content of selenium per mass unit due to the presence of several selenoproteins involved in thyroid hormone metabo- lism. Selenium-containing glutathione peroxidases may play an important role in the antioxidant defence of the thyroid gland by protecting the thyrocytes from any excess hydrogen peroxide (H 2 O 2 ) produced during thyroid hormone synthesis. In cases of severe iodine deficiency (ID), thyroidal iodine autoregulation and the high serum TSH stimulate the production of H 2 O 2. When the selenium availability is below a certain value, the glutathione peroxidase activity may be insufficient to remove the excess H 2 O 2 , which may be one of the mechanisms involved in thyroid gland destruction as seen in areas with combined iodine Correspondence: Inge B€ ulow Pedersen, Department of Endocrinology and Medicine, Aalborg Hospital, Aarhus University Hospital, DK-9000 Aalborg, Denmark. Fax: + 45 99 32 61 61; Tel.: +45 996135; E-mail: I.Bulow@rn.dk © 2013 Blackwell Publishing Ltd 1 Clinical Endocrinology (2013) doi: 10.1111/cen.12185