A high normal TSH is associated with the metabolic syndrome

P>Objective Obesity and insulin resistance are key features of the metabolic syndrome. In euthyroidism, the relationships between TSH and insulin resistance or the metabolic syndrome are less clear. We investigated the associations between TSH and the features and prevalence of the metabolic syndrome in euthyroid German subjects. Methods In a cross-sectional study, glucose metabolism was defined by an oral glucose tolerance test (oGTT) (except for those with evident diabetes) in 1333 subjects with TSH values between 0 center dot 3 and 4 center dot 5 mU/l who did not take any thyroid medication. Lipid parameters were measured, blood pressure and anthromopmetric parameters were taken, and insulin resistance was quantified as HOMA%S. Results TSH was weakly correlated with BMI (R = 0 center dot 061, P = 0 center dot 025). This association remained significant after adjustment for sex, age, and impaired glucose metabolism (P = 0 center dot 002). Subjects with a TSH in the upper normal range (2 center dot 5-4 center dot 5 mU/l, n = 119) had a significantly higher BMI (30 center dot 47 +/- 0 center dot 57 vs. 28 center dot 74 +/- 0 center dot 18 kg/m2, P = 0 center dot 001) and higher fasting triglycerides (1 center dot 583 +/- 0 center dot 082 vs. 1 center dot 422 +/- 0 center dot 024 mmol/l, P = 0 center dot 023), and their likeliness for fulfilling the ATP III criteria of the metabolic syndrome was 1 center dot 7-fold increased (95% CI: 1 center dot 11- 2 center dot 60). Conclusion In euthyroidism, subjects with a TSH in the upper normal range (2 center dot 5-4 center dot 5 mU/l) were more obese, had higher triglycerides, and had an increased likeliness for the metabolic syndrome. Therefore, a TSH below 2 center dot 5 mU/l is associated with a favourable metabolic profile. Whether lowering TSH to levels below 2 center dot 5 mU/l improves metabolism needs to be investigated in intervention trials.