December 16, 2016
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High free T4, low free T3 increase all-cause CV mortality risk

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Adults without overt thyroid disease have an increased risk for all-cause and cardiovascular mortality when they have high free thyroxine and low triiodothyronine concentrations, study data show.

Anette Merke, MS, MD, of the Thyroid Center Bergstrasse in Germany, and colleagues evaluated data from the Ludwigshafen Risk and Cardiovascular Health Study (LURIC; May 1997-June 2001) on 2,507 adults (73% men) without overt thyroid disease who underwent coronary angiography to determine the association between circulating thyroid hormones and all-cause and CV mortality. Follow-up was conducted after 10 years.

Annette Merke
Annette Merke

The mean thyroid hormone levels were 17.29 pmol/L for free T4, 4.81 pmol/L for free T3 and 1.61 mU/L for thyroid-stimulating hormone.

Free T4 levels were positively correlated with diabetes, fasting glucose, lower estimated glomerular filtration rate (eGFR) and Charlson Comorbidity Index.

Sex, age, smoking status, angiographic coronary artery disease, BMI, cholesterol, triglycerides and hypertension were not significantly correlated.

Participants in the lowest quartile of free T3 experienced the highest prevalence rate of CAD. Positively correlations were found regarding age, smoking status, total cholesterol, HDL, LDL and triglycerides, low blood pressure and eGFR were lowest in the lowest quartile of free T3 and highest in the highest quartile of free T3. Charlson Comorbidity Index was highest in the lowest free T3 quartile.

TSH was not significantly correlated with age, sex, smoking status, BMI, diabetes, cholesterol, hypertension and estimated glomerular filtration rate.

Overall, 30.5% of participants died and 62.4% of them died from CV causes. Participants in the highest quartile of free T4 had the highest risk for mortality from all causes (HR = 1.52; 95% CI, 1.25-1.85) and CV causes (HR = 1.77; 95% CI, 1.38-2.2). Participants in the lowest quartile of free T3 had the highest risk for mortality from all-causes and CV causes (HR = 1, reference value) compared to the highest free T3 quartile (HR = 0.54; 95% CI, 0.44-0.67) and CV causes (HR = 0.47; 95% CI, 0.36-0.61).

“More cohort studies are needed with thyroid-healthy patients and with participants of other ethnicities than Caucasians,” Merke told Endocrine Today. “Studies including euthyroid patients with positive thyroid antibodies may evaluate the effect of autoimmune thyroid diseases on mortality. Our study included intermediate to high risk CAD patients; further studies are needed with individuals with or low-risk CAD.” – by Amber Cox

For more information:

Anette Merke, MS, MD, can be reached at annettemerke@gmail.com.

Disclosure: The researchers report no relevant financial disclosures.