The prevalence of the metabolic syndrome increases through the quartiles of thyroid stimulating hormone in a population-based sample of euthyroid subjects.

Objective: The aim of the study was to assess the prevalence and characteristics of metabolic syndrome (MetS) and its elements in relation to TSH in euthyroid subjects.

Materials and methods: In the cross-sectional study, 2,153 euthyroid adults, 47.2 ± 14.5 years (20-94) with no current antithyroid or thyroid replacement therapy were enrolled. All participants filled a questionnaire on past and current morbidities, medication and smoking. Body weight, height, waist circumference, serum TSH, glucose and lipids were measured. The subjects were stratified by quartiles of TSH (QTSH) and the prevalence of the MetS elements was calculated. MetS was determined by the IDF 2005 criteria.

Results: Overweight prevalence was 37.2% (35.2-39.2), obesity in 25.1% (23.3-26.9), abdominal obesity - 61.4% (59.3-63.5), hypertension - 42.1% (38.9-43.1), diabetes/increased fasting glucose - 13.6% (12.1-15), low HDL-cholesterol - 27.6% (25.7-29.5), hypertriglyceridemia - 24.1% (22.3-25.9), MetS - 32.2% (30.2-34.2). MetS was more prevalent in the highest QTSH (34.9%, 30.9-38.9) than the lowest (27%, 23.3-30.9), p < 0.001, as were low HDL-C (32%, 28-35.9 vs. 25%, 21.3-28.7, p < 0.001) and hypertriglyceridemia (26.8%, 23-30.5 vs. 20.4%, 17-23.8, p = 0.015). Each QTSH increased the risk of MetS by 14%, p < 0.001, of hypertriglyceridemia by 20%, p = 0.001 and of low LDL-C by 9%, p = 0.042. Other significant factors for MetS were age, male gender and obesity.

Conclusion: The prevalence of MetS increased with higher QTSH within the euthyroid range, mostly by an increase in the dyslipidemia.