The Claim
Prolonged under-replacement (TSH >5.5 mIU/L) and over-replacement (FT4 >1.9 ng/dL) of thyroid hormone are associated with a time-dependent increase in the risk of incident heart failure, with under-replacement conferring a 5.8-fold higher risk and over-replacement a 2.8-fold higher risk after five years of exposure.
What the research says
Supports is higher
Support is ahead, but a single strong opposing study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
Long-term use of too little or too much thyroid hormone medication is linked to a higher risk of developing heart failure, with the risk increasing the longer the imbalance lasts. After five years, too little hormone raises the risk more than too much.
See the scientific wording
The risk of incident heart failure increases cumulatively over time with both under-replacement and over-replacement of thyroid hormone, with under-replacement (TSH >5.5 mIU/L) showing a 5.8-fold increase in risk after five years and over-replacement (FT4 >1.9 ng/dL) showing a 2.8-fold increase, indicating that prolonged abnormal thyroid hormone exposure has a time-dependent effect on cardiac risk.
What the research says
1 studyStudy: Association between Over- and Under-Replacement with Thyroid Hormone and Incident Heart Failure
This study found that taking too little or too much thyroid hormone medicine over many years can hurt your heart, with too little being especially dangerous — after five years, it more than quintuples your risk of heart failure.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.