People with low normal thyroid function are at elevated risk for components of the metabolic syndrome, according to the first large, community-based study of this population.
Previous research showed an association between overt hypothyroidism and atherosclerotic cardiovascular disease (J. Clin. Endocrinol. Metab. 2003;88:2438–44; N. Engl. J. Med. 2001;344:501–9). However, the current study indicates that thyroid function can influence lipid metabolism even in the euthyroid range, said Dr. Annemieke Roos, of the department of endocrinology at the University Medical Center Groningen (the Netherlands), and her associates.
They assessed 1,581 euthyroid participants from the Prevention of Renal and Vascular End Stage Disease (PREVEND) study (J. Am. Soc. Nephrol. 2000;11:1882–8). People were considered euthyroid if they were within the reference range for thyroid-stimulating hormone (0.35–4.94 mIU/L) and free T4 (9.14–23.81 pmol/L) without taking thyroid medication.
A total of 19% of men and 15% of women met the National Cholesterol Education Program's Adult Treatment Panel (ATP) III criteria for metabolic syndrome. After adjustment for age and gender, free T4 (FT4) was significantly related to four out of five ATP III criteria: abdominal obesity; glucose intolerance/insulin resistance; atherogenic dyslipidemia; and a proinflammatory/prothrombic state. Association with hypertension, was not significant (J. Clin. Endocrinol. Metab. 2007;92:491–6).
After adjustment for insulin resistance, FT4 associations with waist circumference, triglycerides, and HDL cholesterol became weaker but remained significant. The finding suggests “mechanisms other than those associated with insulin resistance underlie the relation of FT4 with these components of the metabolic syndrome.”