(1) Background: Overt and subclinical
hypothyroidism has been associated with increased cardiometabolic risks. Here we further explore whether thyroid function within normal range is associated with cardiometabolic risk factors in a large population-based study. (2) Methods: We screened 24,765 adults participating in health examinations in Taiwan. Participants were grouped according to high-sensitive
thyroid-stimulating hormone (hsTSH) level as: <50th percentile (0.47-1.48 mIU/L, the reference group), 50-60th percentile (1.49-1.68 mIU/L), 60-70th percentile (1.69-1.94 mIU/L), 70-80th percentile (1.95-2.3 mIU/L), 80-90th percentile (2.31-2.93 mIU/L), and >90th percentile (>2.93 mIU/L). Cardiometabolic traits of each percentile were compared with the reference group. (3) Results: Elevated hsTSH levels within normal range were dose-dependently associated with increased body mass index, body fat percentage, waist circumferences, blood pressure,
hemoglobin A1c (HbA1c), fasting
insulin, homeostasis model assessment of
insulin resistance (HOMA-IR), high homeostasis model of assessment of beta-cell (HOMA-β),
triglycerides, total cholesterols,
fibrinogen, and uric
acids (p-for-trend <0.001), but not with fasting
glucose levels. The association remained significant after adjustment of age, sex, and lifestyle. As compared to the reference group, subjects with the highest hsTSH percentile had significantly increased risk of being
overweight (adjusted odds ratio (adjOR): 1.35), increased body fat (adjOR: 1.29),
central obesity (adjOR: 1.36), elevated blood pressure (adjOR: 1.26), high HbA1c (adjOR: 1.20),
hyperinsulinemia (adjOR: 1.75), increased HOMA-IR (adjOR: 1.45), increased HOMA-β (adjOR: 1.40),
hypertriglyceridemia (adjOR: 1.60),
hypercholesterolemia (adjOR: 1.25), elevated
hsCRP (adjOR: 1.34), increased
fibrinogen (adjOR: 1.45),
hyperuricemia (adjOR: 1.47), and
metabolic syndrome (adjOR: 1.42), but significant risk of low fasting
glucose (adjOR: 0.89). Mediation analysis indicates that
insulin resistance mediates the majority of the association between
thyroid hormone status and the
metabolic syndrome. (4) Conclusion: Elevated hsTSH within the normal range is a cardiometabolic risk marker associated with
central obesity,
insulin resistance, elevated blood pressure,
dyslipidemia,
hyperuricemia,
inflammation, and
hypercoagulability.