Clinical and metabolic links between hypothyroidism and metabolic syndrome: a review.

Hypothyroidism and metabolic syndrome frequently coexist and share abnormalities in body weight, lipid metabolism, glucose regulation, and inflammatory signaling. Thyroid hormone deficiency can contribute to dyslipidemia, reduced energy expenditure, and impaired insulin action. By contrast, evidence that obesity, dyslipidemia, or insulin resistance directly causes thyroid dysfunction remains less established and is derived mainly from observational and experimental studies. This critical narrative review integrates current mechanistic and clinical evidence across obesity, dyslipidemia, and insulin resistance. It also examines implications for diagnosis, thyroid hormone replacement, metabolic treatment, monitoring, and future research. Clinical management should restore euthyroidism when thyroid treatment is indicated and address persistent obesity, dyslipidemia, and abnormal glucose metabolism according to their respective clinical indications. Longitudinal and interventional studies are needed to clarify causal direction and identify patient subgroups that may benefit from more individualized management.