Associations between subclinical thyroid dysfunction and cardiovascular risk factors according to age and sex.

Baretella and Blum, Feller and Rodondi contributed equally to this work.

Context
Subclinical thyroid dysfunction (ScTD) comprising subclinical hypothyroidism (SHypo) and subclinical hyperthyroidism (SHyper) has been associated with increased risk for cardiovascular events.
Objective
To assess associations between ScTD and cardiovascular risk factors (cvRFs) according to age and sex.
Design And Setting
Pooled individual participant data analysis of large prospective cohort studies from the Thyroid Studies Collaboration.
Participants
Aged 18 to 103 years with SHypo (TSH >4.50 mU/l, normal fT4) and SHyper (TSH <0.45 mU/l, normal fT4) vs. euthyroid (TSH 0.45-4.50 mU/l).
Interventions
None as this is an observational study.
Main Outcome Measures
cvRFs, i.e. blood pressure, lipid levels, hs-CRP.Results
Of 69,006 participants (mean age 62 years, 55% women, 25% current smokers) from 16 international cohorts, 3,748 (5.4%) had SHypo and 3,428 (5.0%) had SHyper. In both women and men, systolic and diastolic BP were similar regardless of thyroid status. Exceptions were lower diastolic BP in women with SHyper compared to euthyroids (adjusted mean difference [aMD] -1.3 mmHg, 95%CI -2.0 to -0.5), and lower systolic BP in men with SHyper compared to euthyroids (aMD -3.1 mmHg, 95%CI -4.8 to-1.4). In both women and men, lipid levels (total, HDL, LDL cholesterol, triglycerides) and hs-CRP were similar regardless of thyroid status. The only exception were women with SHyper who had a lower LDL cholesterol compared to euthyroids (aMD -0.17 mmol/l, 95%CI -0.29 to -0.05).
Conclusions
Participants with ScTD and euthyroids have similar cvRFs and differences are arguably too small to explain the increased cardiovascular risk in ScTD observed in previous studies.