Prevalence, Incidence, and Risk Factors of Hypothyroidism in Adult Residents of Yazd Greater Area, 2015–2021: Results of Yazd Health Study

Any abnormal change in thyroid hormone levels leads to thyroid disorders, including hyperthyroidism, hypothyroidism, goiter, and so on. Recent studies have reported an increasing prevalence and incidence of thyroid disorders worldwide. This study aims to determine the hypothyroid prevalence, incidence, and risk factors related to this disorder.  Data from a comprehensive prospective cohort study, collected from a population of 10,000 Yazd (Iran) individuals over a period of 6 years (2015-2021) was analyzed. Physicians diagnosed hypothyroidism and reported it. Data processing and preparation were performed using SQL18 and Excel, while STATA17 and SPSS22 software were employed for data analysis. Descriptive statistics, logistic regression, and Chi-square tests were conducted at a significance level of 0.05. The prevalence of hypothyroidism was found to be 93/1000, and the incidence was 15/1000 of the population, respectively. Women had five folds more chance of hypothyroidism (adjusted OR=5.31, 95% CI=3.06-9.19 vs. unadjusted OR=6.28, 95% CI=3.90-10.12), and they usually developed it between the ages of 30 and 39. Eating less (iodized) salt also increased the risk of hypothyroidism (unadjusted OR=1.47, 95% CI=1.02-2.11). Iron supplementation (unadjusted OR=2.09, 95% CI=1.26-3.48) was identified as one of the significant risk factors. Based on our findings in the unadjusted model, tooth brushing once or twice a day increases the chance of hypothyroidism (OR=1.89, P=0.008, and OR=2.12, P=0.016, respectively). Tobacco smoking (unadjusted OR=0.29, 95% CI=0.107-0.786) was also among the factors that need further investigation.  The increasing trend of hypothyroidism is concerning in our population. The high prevalence, particularly among women of childbearing age, is notable.