Smokers have less thyroid autoimmunity and
lower serum thyrotropin concentrations than nonsmokers
(March 2005)
The background of the study. Cigarette smoking
has both inhibitory and stimulatory effects on thyroid function,
and it is a risk factor for Graves’ hyperthyroidism and especially
ophthalmopathy. This study assessed the relationships between smoking
and serum thyrotropin (TSH) and antithyroid antibody concentrations
in a large group of people in the United States.
How the study was done. The study subjects were
16,046 people who had participated in the third National Health
and Nutrition Survey in 1988–1994, and for whom demographic,
smoke exposure, and serum TSH, antithyroid peroxidase (anti-TPO)
antibody, and antithyroglobulin (anti-Tg) antibody results were
available. Smoking or smoke exposure was determined by measuring
serum cotinine, a metabolite of nicotine; people with concentrations
>15 ng/ml were designated as active smokers, and those with concentrations
≤15 ng/ml as nonsmokers.
The results of the study. There were 5134 active
smokers (32 percent) and 10,912 nonsmokers (68 percent). More men
than women were active smokers. Fewer active smokers than nonsmokers
had high (>4.5 mU/L) serum TSH concentrations (2.6 vs. 5.4 percent).
Serum TSH concentrations were low (<0.1 mU/L) in 0.6 percent
of active smokers and 0.3 percent of nonsmokers, and the concentrations
were slightly low (0.1 to 0.4 mU/L) in 2.2 and 1.2 percent, respectively.
Fewer smokers than nonsmokers had high serum antithyroid antibody
concentrations (11 vs. 18 percent). Among subjects with high serum
antithyroid antibody concentrations, the likelihood of a high serum
TSH concentration was lower in active smokers than in nonsmokers.
The conclusions of the study. Among smokers, serum
TSH concentrations are low more often and serum TSH and antithyroid
antibody concentrations are high less often than in nonsmokers.
The original article. Belin RM, Astor BC, Powe
NR, Ladenson PW. Smoke exposure is associated with a lower prevalence
of serum thyroid autoantibodies and thyrotropin concentration elevation
and a higher prevalence of mild thyrotropin concentration suppression
in the third National Health and Nutrition Examination Survey (NHANES
III). J Clin Endocrinol Metab 2004;89:6077-86.
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