Abstract
OBJECTIVE AND DESIGN: We explored the cross-sectional and longitudinal associations of thyroid function within the normal range with cardiovascular disease (CVD) risk factors and adiposity measures. PATIENTS AND MEASUREMENTS: A total of 3483 (50·4% women) participants for the cross-sectional CVD study and 1630 (41·2% women) participants for the cross-sectional body composition substudy were drawn from the Framingham Third Generation Exam 1; 2912 participants (50·1% women) for the longitudinal CVD study and 713 participants (35·9% women) for the longitudinal body composition substudy were drawn from the Framingham Third Generation Exams 1-2. Thyroid function was assessed by thyrotropin [thyroid-stimulating hormone (TSH)] and free thyroxine (fT4) concentrations within the reference range at Exam 1. The associations between thyroid function and CVD risk factors were modelled via multivariable-adjusted regression models. Multivariable adjustment included age, sex, current smoking, postmenopausal status and BMI. RESULTS: Cross-sectionally, higher TSH concentration was associated with increased odds of hypertriglyceridaemia [odds ratio (OR)=1·10], and higher BMI (β = 0·19 kg/m(2) ), total cholesterol (β = 0·05 mmol/l), triglycerides (β = 0·0006 mmol/l) and subcutaneous adipose tissue (SAT) volume (β = 38·8 cm(3) ) (all P < 0·05). Cross-sectionally, fT4 was inversely associated with metabolic and adiposity-related CVD risk factors, including obesity (OR = 1·17), hypertriglyceridaemia (OR = 1·09), BMI (β = 0·42 kg/m(2) ), total cholesterol (β = 0·05 mmol/l), triglycerides (β = 0·0002 mmol/l), visceral adipose tissue (VAT) volume (β = -20·7 cm(3) ) and attenuation (0·17 HU) and VAT/SAT ratio (β = -0·01) (all P < 0·05). However, during 6·1 years of follow-up, baseline TSH and fT4 levels were not longitudinally associated with CVD risk factors and adiposity measures. CONCLUSIONS: Thyroid function within the normal range is cross-sectionally, but not longitudinally, associated with CVD risk factors and adiposity measures.