title: Does iodine excess lead to hypothyroidism? Evidence from a case-control study in India.
abstract: BACKGROUND
  Iodine deficiency disorders have been known to mankind since antiquity and various researchers elucidated the role of iodine in its causation. However, recent evidence shows that the entire control program ignored multi-causality and association of increased iodine intake with hypothyroidism. This study was conducted to assess differences of iodine intake as measured by urinary iodine excretion (UIE) between cases of hypothyroidism and healthy controls.
  
  
  METHODS
  A case-control study was conducted with three groups (cases, hospital controls and community controls) in two cities of India. Patients with overt hypothyroidism were cases (n = 150) and were compared with age, sex and socioeconomic status-matched hospital (n = 154) and community (n = 488) controls. Thyroid function tests (T3, T4, TSH) were used as diagnostic and inclusion criteria. TPOAb and UIE estimation were carried out for all study participants.
  
  
  RESULTS
  Mean values of TPOAb and UIE were higher in cases as compared to hospital controls as well as community controls (p <0.05). With a cut off of 34 IU/mL for TPOAb, more cases had an anti-TPO level >34 as compared to hospital controls (p <0.001) as well as community controls (p <0.001); OR, 0.06 (95% CI, 0.03, 0.12) and 0.08 (0.05, 0.12), respectively. For UIE cut-off of 300 μg/L, more cases than hospital controls (p = 0.090) and community controls (p = 0.001) had higher levels; OR, 0.671, (0.422, 1.066) and 0.509, (0.348, 0.744), respectively.
  
  
  CONCLUSIONS
  The study has clearly shown that cases of hypothyroidism are associated with excess iodine intake. Cohort studies to generate further evidence and an eco-social epidemiological approach have been suggested as the way forward.
authors.affiliation: Office of Director General, Department of Haematology, New Delhi, India. Electronic address: dratulkotwal@gmail.com.
authors.forename: Atul
authors.initials: A
authors.lastname: Kotwal
authors.affiliation: Sir Gangaram Hospital Professor and Head, Department of Haematology, New Delhi, India.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Kotwal
authors.affiliation: Office of Director General, Department of Haematology, New Delhi, India.
authors.forename: Rajat
authors.initials: R
authors.lastname: Prakash
authors.affiliation: Office of Director General, Department of Haematology, New Delhi, India.
authors.forename: Narendra
authors.initials: N
authors.lastname: Kotwal
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000209:etiology* / Q000473:pathology; D007194:India; D007455:Iodine / Q000009:adverse effects*; D008297:Male
chemical_list: D007455:Iodine
keywords: Autoimmune thyroiditis; Case-control study; Hypothyroidism; Iodine deficiency disorders; Salt iodization; Urinary iodine excretion