Endocrine Abstracts

Background: The metabolic syndrome (MetS) is a combination of unfavourable health factors including abdominal obesity, dyslipidaemia, hypertension and impaired fasting glucose. Several small-scale studies have reported a relationship between thyroid function and some MetS components or suggested that serum FT3 levels within the normal range were independently associated with insulin resistance. We assessed how thyroid function relates to the prevalence of MetS in a large population-based study.

Methods: Data of 26,719 western European participants aged 18-80 years from the Dutch LifeLines Cohort study, all with normal TSH, FT4 and FT3 levels (electrochemiluminescent immunoassay, Roche Modular E170 Analyzer), were available. MetS was defined with the revised NCEP ATP III criteria. We calculated prevalence of all MetS components according to FT4 and FT3 quartiles.

Results: At similar TSH levels and age (mean 45 yrs), men had significantly higher levels of FT4, FT3, blood pressure (BP), heart rate, total and LDL-cholesterol, triglycerides (TG), and creatinine, but lower HDL-cholesterol compared to women (all P<0.001). In total, 9.1% of women and 10.2% of men were treated with BP-lowering agents. In men, lower FT4 levels were associated with higher prevalence of all MetS components. The lowest FT4 quartile was associated with the highest prevalence of elevated BP (60%), elevated glucose (22.7%), waist circumference (33.4%) and TG (30.2%), low HDL-cholesterol (26.5%), and MetS (27.7%). In women, the lowest FT4 quartile was only associated with elevated TG (11.2%), waist circumference (47.4%), and MetS (13.8%). In contrast, higher FT3 levels were associated only with low HDL-cholesterol in both sexes, and with a higher percentage of participants with ≥3 MetS components (21.6% in men, 12.4% in women).

Conclusions: Levels of FT4, but not FT3, were inversely associated with all components of the metabolic syndrome in men, and with elevated TG, waist, and overall MetS in women.