Subclinical thyroid dysfunction and cardiovascular outcomes among prospective cohort studies

Area of Science:

• Endocrinology
• Cardiovascular Medicine
• Epidemiology

Background:

• Subclinical thyroid dysfunction, characterized by abnormal Thyroid-Stimulating Hormone (TSH) levels with normal thyroxine (FT4), is common.
• Previous studies on its cardiovascular impact have yielded inconsistent results.
• Individual participant data (IPD) analyses offer a more robust approach to clarify these associations.

Purpose of the Study:

• To precisely estimate the cardiovascular risks associated with subclinical hypothyroidism and subclinical hyperthyroidism.
• To identify specific TSH level thresholds indicative of increased cardiovascular risk.
• To inform clinical decision-making regarding thyroid medication initiation.

Main Methods:

• Systematic review and meta-analysis of original cohort studies.
• Pooling of individual participant data (IPD) from over 70,000 individuals.
• Analysis of cardiovascular outcomes including coronary heart disease events/mortality, heart failure, and atrial fibrillation.

Main Results:

• Subclinical hypothyroidism is linked to increased risk of coronary heart disease (CHD) events, CHD mortality, and heart failure (HF), particularly with TSH ≥10.0 mIU/L.
• Subclinical hyperthyroidism is associated with higher risks of total mortality, CHD mortality, HF, and atrial fibrillation, especially with TSH <0.10 mIU/L.
• Both conditions pose greater cardiovascular risks with more pronounced thyroid dysfunction.

Conclusions:

• Subclinical thyroid dysfunction significantly elevates cardiovascular risk, with risk escalating at higher TSH levels for hypothyroidism and lower levels for hyperthyroidism.
• Identified TSH thresholds provide valuable guidance for considering thyroid medication, though clinical decisions require caution.
• Ongoing randomized controlled trials, such as the TRUST trial, will further elucidate the benefits of thyroid hormone replacement.