Trends in the incidence and prevalence of thyroid dysfunction over 18 years and projections for 2030: the Tehran...

Thyroid dysfunction is a common endocrine disorder with significant systemic health consequences. Despite its high burden, data on the long-term prevalence, incidence, and risk factors for thyroid dysfunction remain limited and outdated.

A total of 5483 adults aged ≥ 20 years from the Tehran Thyroid Study cohort were followed over 18 years. Prevalence and incidence rates were calculated and stratified by age, sex, anti-TPO status, TSH level, smoking, and BMI. Risk factors were analyzed using Cox proportional hazards models, and a mixed Poisson model was used to project prevalence trends to 2030.

Over 18 years of follow-up, the incidence of subclinical hypothyroidism was 8.7 (95% CI: 7.9-9.4), overt hypothyroidism 4.6 (95% CI: 4.1-5.1), subclinical hyperthyroidism 2.6 (95% CI: 2.2-3.0), and overt hyperthyroidism 2.7 (95% CI: 2.3-3.1) per 1000 person-years. There was no association between age and serum TSH level. Female sex (HR: 4.38; 95%CI: 2.38-8.06), anti-TPO positivity (HR: 3.50; 95%CI: 2.42-5.06), and baseline TSH within 2.0-5.06 mIU/L range (HR: 4.26; 95%CI: 2.84-6.39) were significant predictors of overt hypothyroidism. These factors also significantly increased the risk of subclinical hypothyroidism (P < 0.001). Current smoking was associated with an increased risk, while baseline TSH level between 2.0 and 5.06 mIU/L was associated with a decreased risk of subclinical hyperthyroidism (P < 0.001). From 1999 to 2018, the prevalence of hypothyroid disorders increased steadily, whereas the prevalence of hyperthyroid disorders declined. Projections to 2030 estimate a 60% increase in subclinical and overt hypothyroidism prevalence compared to 2018, while hyperthyroidism prevalence is expected to decline.

This 18-year population-based cohort provides the most comprehensive long-term data on thyroid dysfunctions. The prevalence of hypothyroidism is rising and is projected to increase substantially by 2030, underscoring the need for targeted public health strategies, early detection, and further investigation into modifiable risk factors.

The online version contains supplementary material available at 10.1007/s40200-026-01939-y.