Hormone Therapy History Linked to Higher Thyroid Disorder Burden in Postmenopausal Korean Women

Millions of women pass through menopause each year, and many of them face a quiet medical crossroads: whether to use menopausal hormone therapy to ease hot flashes, sleep disruption, and other symptoms, while wondering what that treatment might mean for the rest of their endocrine system. A new analysis of nationally representative South Korean health survey data now adds a fresh and provocative data point to that conversation. Researchers report that postmenopausal women who said they had ever taken female hormone medications carried a substantially higher burden of thyroid disorders than women who never reported such use, a finding that is sure to draw attention from clinicians and patients alike, even as the study’s authors caution that it cannot prove the hormones themselves are to blame.

The study, published as an open-access research article in BMC Endocrine Disorders, drew on the Korea National Health and Nutrition Examination Survey, known as KNHANES, specifically the fourth wave conducted between 2007 and 2009. The investigators, led by Ziran Qiu of the Department of Breast and Thyroid Surgery at Loudi Central Hospital in Hunan, China, together with colleagues including corresponding author Na Jin, focused on postmenopausal women, a group in which both menopausal hormone therapy and thyroid disease converge with unusual frequency. Thyroid disorders, which range from underactive and overactive gland function to nodules and autoimmune inflammation, are markedly more common in women than in men, and their prevalence rises with age, making the postmenopausal population a natural setting for asking whether exogenous hormones tip the balance.

The analytical sample comprised 3,974 postmenopausal women, of whom 582 reported a history of using female hormone medication. The exposure was deliberately simple: a questionnaire item recording whether the participant had ever taken female hormone drugs. Importantly, the survey did not capture whether use was current, which formulation was taken, at what dose, or for how long, a limitation that shapes how the results can be interpreted. The outcomes were equally grounded in self-report: thyroid disorders diagnosed by a doctor served as the primary endpoint, while current thyroid disorder, lifetime thyroid disorder, and currently treated thyroid disorder served as secondary endpoints. This reliance on questionnaire-defined disease means the study measures the burden of recognized and recorded thyroid illness rather than laboratory-confirmed thyroid dysfunction in the moment.

The headline numbers are striking. Weighted prevalence of doctor-diagnosed thyroid disorder was 10.87 percent among women with a hormone therapy history versus 6.87 percent among women without one. Current thyroid disorder showed a similar gap, 6.79 percent versus 3.79 percent, as did lifetime thyroid disorder at 10.95 percent versus 6.96 percent and treated thyroid disorder at 4.88 percent versus 2.95 percent. In every case, women reporting prior hormone medication use carried roughly a one-and-a-half to nearly two-fold heavier burden of thyroid disease on the raw, survey-weighted scale.

Because raw differences in observational data can easily reflect age, body weight, income, reproductive history, or the simple fact of seeing doctors more often, the team turned to survey-weighted logistic regression, the standard tool for estimating associations in complex national surveys. Their models adjusted for demographic, socioeconomic, metabolic, reproductive, and survey-year factors. To guard against the statistical trap of cherry-picking significant results across multiple tests, they applied Benjamini-Hochberg correction, computing q values that control the expected proportion of false discoveries across the four outcomes. After adjustment, a history of female hormone therapy remained associated with doctor-diagnosed thyroid disorder with an adjusted odds ratio of 1.52 and a 95 percent confidence interval of 1.06 to 2.16, with a q value of 0.031. The estimate for current thyroid disorder was even stronger, at an odds ratio of 1.75 with a confidence interval of 1.09 to 2.83, and lifetime thyroid disorder yielded an odds ratio of 1.50 with a confidence interval of 1.06 to 2.14, both also surviving the false discovery correction at q equal to 0.031. The estimate for currently treated thyroid disorder was directionally similar but less statistically secure, at an odds ratio of 1.60 with a confidence interval spanning 0.96 to 2.68 and a q value of 0.071.

Recognizing that any single modeling choice can swing results, the researchers ran an unusually thorough battery of sensitivity analyses. When they expanded the covariate set further, the primary estimate attenuated to an odds ratio of 1.38 with a confidence interval of 0.96 to 2.00, no longer excluding the possibility of no association. When they adjusted for healthcare contact, an attempt to account for the possibility that hormone therapy users simply interact with the medical system more and therefore get diagnosed more often, the association held at an odds ratio of 1.46 with a confidence interval of 1.01 to 2.10. Restricting the analysis to narrower age bands, however, produced estimates that crossed the null, suggesting the signal may be sensitive to the age composition of the sample. Adding gravidity, the number of times a woman had been pregnant, to the adjustment left the estimate essentially unchanged at an odds ratio of 1.52 with a confidence interval of 1.05 to 2.20. Exploratory analyses of treatment duration returned heterogeneous results, offering no consistent picture of whether longer exposure carried greater risk.

What might connect ovarian hormone preparations and the thyroid gland biologically? The mechanistic story is plausible but unresolved. Estrogen influences thyroid physiology in several documented ways: it can stimulate thyroglobulin, the protein scaffold on which thyroid hormones are synthesized, and it modulates immune activity in a gland where autoimmune disease, particularly Hashimoto’s thyroiditis, is disproportionately common in women. Hormone therapy could also plausibly promote thyroid growth or nodule formation in a gland already rich in estrogen receptors. Conversely, the association could run in the opposite causal direction: women with thyroid symptoms such as fatigue, weight change, or mood disturbance might seek menopausal symptom relief through hormone therapy, or their thyroid conditions might simply be diagnosed around the same life stage. Residual confounding by health-seeking behavior, physician vigilance, or unmeasured metabolic traits remains a live possibility in any cross-sectional design.

The authors are explicit about the limits of their evidence. Because the exposure and outcomes were both self-reported and captured at a single point in time, the study cannot establish temporality, let alone causality. It cannot distinguish whether hormone therapy preceded the thyroid disorder, followed it, or merely co-occurred with it. The questionnaire also could not identify current users or treatment details, blurring any dose or duration effects. Yet the consistency of the association across three of four endpoints, its survival of false discovery correction, and its persistence under healthcare-contact adjustment give the finding enough weight that it should not be dismissed as statistical noise. At the same time, the attenuation under expanded adjustment and the null results in age-restricted analyses are honest reminders that the true effect, if any, is likely modest and context-dependent.

For clinicians and the millions of postmenopausal women weighing hormone therapy, the practical takeaway is one of measured vigilance rather than alarm. The study’s authors state plainly that their findings do not support universal thyroid screening for women with a hormone therapy history, nor do they justify changing menopausal hormone therapy decisions solely on the basis of that history. Standard practice, in which thyroid function is evaluated when symptoms or clinical findings warrant it, remains the appropriate course. What the research does provide is a well-powered, nationally representative East Asian data point in a literature long dominated by Western cohorts, and a clear template for the kind of study needed next: prospective, longitudinal designs with pharmacy-verified hormone exposure, laboratory-measured thyroid function, and careful sequencing of treatment and diagnosis. Until such evidence arrives, the association between hormone therapy history and thyroid disorder burden in postmenopausal Korean women stands as an intriguing signal, a question mark that modern endocrinology will now be pressed to resolve.

Subject of Research: The association between self-reported menopausal hormone therapy history and thyroid disorder prevalence among postmenopausal Korean women in the KNHANES IV survey.

Article Title: Self-reported female hormone therapy history and thyroid disorder burden among postmenopausal Korean women: a cross-sectional KNHANES IV study

Article References: Qiu, Z., Long, H., Li, R., Yang, J., Cao, W., Chen, S., & Jin, N. (2026). Self-reported female hormone therapy history and thyroid disorder burden among postmenopausal Korean women: a cross-sectional KNHANES IV study. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-026-02540-3

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02540-3

Keywords: menopausal hormone therapy, thyroid disorder, postmenopausal women, KNHANES, cross-sectional study, South Korea, endocrinology, odds ratio, thyroid screening, estrogen, women's health, observational study