Hormonal Contraceptive Use Is Associated With a Decreased Incidence of Hypothyroidism

Hypothyroidism is one of the most common endocrine disorders affecting 5 to 10 times more women than men. Given this higher incidence in women, it is possible that hormonal differences or medications more commonly used by women may play a role in the risk of developing hypothyroidism. We hypothesized that hormonal contraception affects the risk of developing hypothyroidism.

Using the TriNetX database, we developed a case-control study and identified women aged 18 to 45 years in 4 distinct groups: (1) estrogen-progestin contraceptive (EPC) use, (2) progestin-only contraceptive (POC) use, (3) progestin-containing intrauterine device (IUD) use, and (4) controls. For each group, we ascertained data including the diagnosis of hypothyroidism, alcohol use, tobacco use, and body mass index.

We identified 18 578 patients with sufficient data: EPC use, n = 5849; POC use, n = 5052; IUD use, n = 1000; and controls, n = 6677. A total of 118 individuals (1.8%) in the control group and 165 individuals (1.4%) who received hormonal contraception developed hypothyroidism. After using a logistic model to account for cofounding variables, all forms of hormonal contraception (EPC, POC, and IUD) had a protective effect against the diagnosis of hypothyroidism. POC and IUD uses had the greatest protective effect, with odds ratios of 0.14 and 0.12, respectively. EPC had a less pronounced but still significant effect, with an odds ratio of 0.30 (P < .001).

This study of >18 000 women and the risk of developing hypothyroidism demonstrates a protective effect of hormonal contraceptive use. Our data, both unadjusted and adjusted using a logistic model to account for cofounding variables, suggest that the use of hormonal contraception, in any form, decreases the risk of developing hypothyroidism.