Objective: The role of smoking in the pathogenesis of thyroid enlargement is currently under debate. It has been hypothesized that the effect of smoking on increased thyroid volume is larger in regions with than in regions without iodine deficiency. The aim of this paper was to investigate the association of smoking with thyroid volume progression and incident goiter for different age-strata in a region with improved iodine supply.
Design and methods: The population-based Study of Health in Pomerania compromised 3300 subjects with complete 5-year examination follow-up. Data from 2484 participants without known history of thyroid disorder or thyroid medication were analyzed. Thyroid size was evaluated by ultrasound. Determinants of thyroid volume progression and incident goiter, i.e., newly occurred goiter between baseline and follow-up, were analyzed by linear and logistic regression respectively.
Results: Participants aged 20-39 years who were current smokers at baseline and at follow-up had a lower risk of incident goiter (odds ratio: 0.33; 95% confidence interval (CI): 0.15; 0.71; P=0.005). In this subpopulation, age was inversely related to thyroid volume progression. In subjects aged 60-79 years, smoking at baseline and follow-up was a risk factor for thyroid volume progression (beta: 3.37; 95% CI: 0.84; 5.89; P=0.009). After exclusion of individuals who had actual goiter in ultrasound at baseline, this association disappeared.
Conclusion: We conclude that the inverse association between smoking and goiter in young adults and the lacking association of smoking with goiter and thyroid volume progression in adult non-goitrous subjects indicate that smoking has a declining impact on thyroid growth in the study region. Our findings mirror the improved iodine supply of Northeast Germany.