Is fluoride-induced hyperthyroidism a cause of psychosis among East African immigrants to Scandinavia? Karl Erik Zachariassen a, * , Trond Peder Flaten b a Laboratory of Ecophysiology and Toxicology, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway b Department of Chemistry, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway article info Article history: Received 17 November 2008 Accepted 19 November 2008 Available online xxxx summary East African immigrants to Scandinavia are admitted to mental hospitals far more frequently than native Scandinavians. Most of these patients are admitted for psychosis, commonly ascribed to problems adapt- ing to the new culture. However, psychosis is also known to be associated with hyperthyroidism, and the high frequency of psychosis among East Africans in Scandinavia may at least in part be due to hyperthy- roidism rather than cultural problems. Large areas in East Africa are notorious for high natural concen- trations of fluoride in water and plants. Fluoride inhibits the production of thyroid hormones. To maintain normal thyroxin levels the body increases the capacity for thyroxin production. Goitre is caused by such a compensatory mechanism, and endemic goitre is widespread in many high-fluoride areas, even where dietary access to iodine is adequate. When people from such areas arrive in a low-fluoride area, their elevated capacity to produce thyroid hormones may lead to hyperthyroidism and subsequently to psychosis. Ó 2009 Elsevier Ltd. All rights reserved. Background of the hypothesis Asylum seekers and immigrants in Scandinavia are admitted to mental hospitals for psychotic disorders up to ten times more fre- quently than native Scandinavians [1–3]. The high frequency of psychosis among immigrants is usually explained as a result of traumatic experiences in their countries of origin, problems with adapting to a new culture, and the fact that immigrants are often socially underprivileged [4,5]. The frequency of psychotic disorders seems to be particularly high among immigrants from East Africa [4,6], and in this group of immigrants it seems particularly common to explain psychotic behaviour as a result of cultural collision and problems with social adaptation [4,5]. However, some studies [6], but not all [4], indicate that the high frequency of mental disorders is not seen in second generation immigrants, who often have the same social standing as their parents. Hence, although social factors are likely to be of importance, there may also be other causes. In this article, we put forward the hypothesis that hyperthyroidism, caused by fluoride exposure in their home country, is a cause of psychosis among immigrants from East Africa and other high-fluoride regions. Hyperthyroidism is a persistent elevation of the blood levels of the thyroxin hormones T3 and T4, which are produced in the thy- roid gland [7]. These hormones are notable for their high content of iodine; three atoms in each molecule of T3 and four in T4. Via a negative feedback mechanism the function of the thyroid gland is controlled by the thyroid stimulating hormone (TSH) from the pituitary gland. A suboptimal blood level of thyroid hormones stimulates the release of TSH, which in turn stimulates the thyroid gland to produce more of its hormones [7]. A chronic deficit of iodine causes a permanent reduction in the levels of thyroid hormones in the blood, a condition known as hypothyroidism. The resulting elevated level of TSH will increase the capacity of the thyroid gland to produce thyroxin, and some- times also cause the thyroid gland to develop goitre [8]. If a person with an elevated capacity for production of thyroid hormones experiences an increased dietary intake of iodine, the thyroid gland will produce increased amounts of thyroid hormones, sometimes resulting in a shift from a hypothyroid to a hyperthyroid condition. An elevated capacity for thyroxin production and hyperthyroidism may occur even without a manifest goitre [7]. Hyperthyroidism is characterized by a number of physiological disturbances, including mental disorders. Some hyperthyroid pa- tients develop behavioural problems, paranoia and an explosive temper [9–11]. In spite of the characteristic and often dramatic symptoms, such a psychotic disturbance may be present for years without being properly diagnosed. The consequences can be tragic, involving for example broken marriages and serious violent crime. The hypothesis A high frequency of hyperthyroidism among immigrants from East Africa could be related to the chemical environment in their 0306-9877/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2008.11.039 * Corresponding author. Tel.: +47 73 59 62 99; fax: +47 73 59 13 09. E-mail address: karl.erik.zachariassen@bio.ntnu.no (K.E. Zachariassen). Medical Hypotheses 72 (2009) 501–503 Contents lists available at ScienceDirect Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy