Association between obesity and hypothyroidism: A comprehensive review

Obesity and hypothyroidism are among the most prevalent chronic disorders worldwide and frequently coexist in clinical practice. Although hypothyroidism has traditionally been regarded as a contributing factor to weight gain because of its effects on basal metabolic rate and energy expenditure, accumulating evidence suggests that obesity itself may substantially influence thyroid function through endocrine, metabolic, and inflammatory mechanisms. This comprehensive review summarizes current evidence regarding the association between obesity and hypothyroidism, focusing on epidemiological findings, pathophysiological mechanisms, thyroid autoimmunity, metabolic phenotypes, pediatric and adult populations, and therapeutic implications. Evidence from systematic reviews, longitudinal cohort studies, Mendelian randomization analyses, and observational investigations indicates that obesity is associated with an increased prevalence of both overt and subclinical hypothyroidism. Adipose tissue-derived mediators, particularly leptin and pro-inflammatory cytokines, appear to influence the hypothalamic–pituitary–thyroid axis, alter peripheral thyroid hormone metabolism, and promote autoimmune thyroid disease. However, mild elevations of thyroid-stimulating hormone observed in many obese individuals, especially children, often represent adaptive physiological responses rather than permanent thyroid dysfunction and frequently normalize following weight reduction. Current evidence further suggests that improving metabolic health and reducing excess body weight have greater effects on thyroid function than thyroid hormone replacement alone in patients without overt hypothyroidism. Overall, the available literature supports a bidirectional but predominantly obesity-driven relationship between obesity and thyroid dysfunction. Understanding these mechanisms may improve diagnostic accuracy, reduce unnecessary pharmacological treatment, and facilitate individualized management strategies for patients presenting with both conditions.