Interaction between cigarette smoking and iodine intake and their impact on thyroid function.
OBJECTIVE
Several population-based studies in iodine-deficient areas have shown an association between smoking and thyroid function. There are no population-based studies about the effects of smoking in iodine-sufficient areas. We examined the effect of smoking on thyroid function and the association with iodine intake in Korea, an area with sufficient iodine intake, much more than recommended by the World Health Organization (WHO).


METHODS
Of 5018 subjects in a population-based cohort, we included 3399 who had no history of thyroid disease were not taking thyroid medication and whose blood samples were available for measurement of thyroid function.


METHODS
Thyroid function test, questionnaire about smoking status and dietary intake.


RESULTS
Of 3399 subjects, 397(11.7%) had subclinical hypothyroidism (SCH). Female sex was an independent risk factor for SCH. Multivariate analysis in female subjects showed the following were independent risk factors for SCH: older age, positive antithyroid peroxidase (anti-TPO) antibody status and iodine intake, whereas current smoking was inversely related with SCH. However, in male subjects, only age showed a weak association with SCH. When the interaction between smoking and other risk factors was analysed, smoking showed no association with anti-TPO antibody status, whereas it showed a significant negative interaction with iodine intake (odds ratio, 0.930; 95% CI, 0.869-0.996; P = 0.037). Furthermore, the risk for SCH was observed only in the never-smoker group; however, it was abolished in current- and ex-smoker groups.


CONCLUSIONS
Cigarette smoking was associated with a lower prevalence of SCH in a negative interaction with iodine intake.
Cho
Nam H
NH
Department of Preventive Medicine, Ajou University School of Medicine & Hospital, Suwon, Korea.
Choi
Hoon Sung
HS
Kim
Kyung Won
KW
Kim
Hyung-Lae
HL
Lee
Soo-Youn
SY
Choi
Sung Hee
SH
Lim
Soo
S
Park
Young Joo
YJ
Park
Do Joon
DJ
Jang
Hak C
HC
Cho
Bo Youn
BY
D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004435:Eating / Q000502:physiology*; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000453:epidemiology / Q000378:metabolism; D007453:Iodide Peroxidase / Q000276:immunology; D007455:Iodine / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D015995:Prevalence; D012907:Smoking / Q000453:epidemiology / Q000378:metabolism*; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000378:metabolism / Q000502:physiology*
D001323:Autoantibodies; D007455:Iodine; D007453:Iodide Peroxidase