The Association Between Estrogen‐Containing Oral Contraceptive Pills and Hypothyroidism

<b>Background:</b> Hypothyroidism is an endocrine disorder that affects 10 times more females than males, with substantial health impacts. The role of estrogen-containing oral contraceptives (OCPs) in influencing thyroid function remains relatively underexplored. This study investigated the association between estrogen-containing OCP use and hypothyroidism in the female population in Qatar. <b>Methods:</b> We utilized data from the Qatar Biobank to conduct a cross-sectional study of 1001 female participants with a current or previous history of estrogen-containing OCP use. The thyroid function of the participants was evaluated via thyroid function test parameters (thyroid stimulating hormone (TSH) and free tetraiodothyronine (fT4)) as outcomes, and sex hormone-binding globulin (SHBG) levels as a proxy indicator of OCP use. We adjusted for confounders such as age, ethnicity, and type 2 diabetes mellitus status via multivariable logistic regression to determine the odds of hypothyroidism associated with SHBG levels. <b>Results:</b> Among the 1001 participants, 34 (3.4%) met the diagnostic criteria for hypothyroidism. Multinomial logistic regression revealed no increased odds of hypothyroidism at the 90th percentile cutoff for SHBG levels (OR 1.00, 95% CI 0.29-3.50). However, at the 95th percentile of SHBG values, there was 46% higher odds of hypothyroidism (OR 1.46, 95% CI 0.33-6.54) and an over tenfold increase at the 99th percentile (OR 10.07, 95% CI 1.94-52.45, <i>p</i>=0.006). Other variables, such as age, ethnicity, and diabetes status, were not associated with SHBG levels. Non-Qatari Arabs had higher odds of hypothyroidism compared with that of Qataris (OR 8.06, 95% CI 0.84-77.54, <i>p</i> value 0.071). <b>Conclusion:</b> This study offers evidence that SHBG levels can be used to indicate estrogen-containing OCP use. Furthermore, higher SHBG levels are associated with higher odds of hypothyroidism among OCP users, and the odds of hypothyroidism vary across different ethnicities. These findings highlight the need for further research to explore the mechanisms linking OCP use to thyroid dysfunction and to investigate other potential risk factors.