Exploring the Cross-Sectional Association Between Hypothyroidism and Circadian Syndrome: Insights from NHANES 2007-2012.

Background: Circadian Syndrome (CircS) encompasses a range of cardiometabolic risk factors that contribute to an increased susceptibility to cardiovascular diseases and type 2 diabetes. Understanding the factors that underpin CircS is essential. This study primarily aims to examine the association between hypothyroidism and CircS in adults. A secondary analysis compares this association with that between hypothyroidism and Metabolic Syndrome (MetS). Additionally, the dose-response relationship between serum free thyroxine (FT4) levels and CircS probability is explored.

Methods: This cross-sectional study includes 4050 National Health and Nutrition Examination Survey (NHANES) participants (2007-2012). Hypothyroidism was classified into (1) drug-managed, (2) non-drug-managed (NDM) primary, and (3) NDM central hypothyroidism, based on self-reported medication use and serum TSH/FT4 levels. CircS was defined as having ≥5 of its eight components, including MetS criteria, depression, short sleep, and non-alcoholic fatty liver disease.

Results: Our results showed that hypothyroidism was significantly associated with CircS (OR: 1.58, 95% CI 1.26-1.98) and MetS (OR: 1.19, 95% CI 1.01-1.42). An inverse, non-linear relationship between serum FT4 levels and the probability of CircS was observed.

Conclusions: The results underscore a significant association between hypothyroidism and CircS and MetS, with FT4 levels inversely related to CircS probability. These findings highlight hypothyroidism's potential role in CircS pathogenesis and prevention.