Smoking and environmental iodine as risk factors for thyroiditis among parous women

Eur J Epidemiol. 2007;22(7):467-72. doi: 10.1007/s10654-007-9142-1. Epub 2007 Jun 8.

Abstract

Objective: To elucidate whether exposure to some environmental factors, i.e. cigarette smoking and iodine deficiency influence the risk of thyroiditis.

Methods: We identified a cohort of 874, 507 parous women with self-reported information on smoking during pregnancy registered in the Swedish Medical Birth Registry from September 1983 through December 1997. Hospital diagnoses of thyroiditis (n = 286) and hypothyroidism (n = 690) following entry into the cohort were identified by record-linkage with the national Inpatient Registry. The hazard ratio (HR) of smokers compared to non-smokers and the corresponding 95% confidence limits (CL) were estimated by Cox regression.

Results: Smoking was inversely associated with risk of overt thyroiditis (adjusted HR = 0.72; CL = 0.54-0.95), even when diagnoses of primary hypothyroidism were included. However, a diagnosis of thyroiditis within 6 months from a childbirth was positively associated with smoking (adjusted HR = 1.88; CL = 0.94-3.76). Being born in areas of endemic goiter was not associated to hospital admission for thyroiditis. Thyroiditis patients who were smokers had more often than non-smokers a co-morbidity with other autoimmune disorders.

Conclusions: Smoking may increase the risk of thyroiditis occurring in the post-partum period and influence the clinical expression of other thyroiditis, especially when occurring as part of a polymorphic autoimmune disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autoimmune Diseases / epidemiology
  • Birth Certificates
  • Comorbidity
  • Endemic Diseases
  • Female
  • Humans
  • Hypothyroidism / diagnosis
  • Hypothyroidism / epidemiology
  • Hypothyroidism / immunology
  • Iodine / deficiency*
  • Postpartum Thyroiditis / diagnosis
  • Postpartum Thyroiditis / epidemiology*
  • Postpartum Thyroiditis / immunology
  • Pregnancy
  • Proportional Hazards Models
  • Prospective Studies
  • Registries
  • Risk Assessment
  • Risk Factors
  • Smoking / adverse effects*
  • Sweden / epidemiology

Substances

  • Iodine