Smoking and environmental iodine as risk factors for thyroiditis among parous women.
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.
Galanti
Maria Rosaria
MR
Clinical Epidemiology Unit, Department of Medicine, Karolinska Institutet, Karolinska Hospital M9:01, Stockholm, 171 76, Sweden. rosaria.galanti@sll.se
Cnattingius
Sven
S
Granath
Fredrik
F
Ekbom-Schnell
Annika
A
Ekbom
Anders
A
D001327:Autoimmune Diseases / Q000453:epidemiology; D001719:Birth Certificates; D015897:Comorbidity; D019353:Endemic Diseases; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis / Q000453:epidemiology / Q000276:immunology; D007455:Iodine / Q000172:deficiency*; D050032:Postpartum Thyroiditis / Q000175:diagnosis / Q000453:epidemiology* / Q000276:immunology; D011247:Pregnancy; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013548:Sweden / Q000453:epidemiology
D007455:Iodine