Higher Free Thyroxine Levels In Middle-Aged And Elderly People May Be Associated With Greater Risk For Atherosclerosis
Can free thyroxine levels identify those at-risk?
Thyroid Hormone Levels Boost Risk of Artery Hardening
ORLANDO -- Middle-aged and elderly people with higher free thyroxine levels may be at a greater risk for developing atherosclerosis, a researcher said here.
According to a large, population-based study in the Netherlands, the risk of atherosclerotic cardiovascular mortality increased with higher levels of free thyroxine (HR 2.35; 95% CI 1.61-3.41 per 1 ng/dl) and lower thyroid-stimulating hormone levels (HR 0.92; 95% CI 0.84-1.00 per 1 logTSH), said Arjola Bano, MD, a PhD candidate at Erasmus Medical Center in Rotterdam, the Netherlands.
"Higher levels of thyroid hormone are also associated with an increased risk of subclinical and clinical manifestations of atherosclerosis. Interestingly, these results were consistent even in the normal range of thyroid function," she said during a presentation at ENDO 2017.
In an interview with to MedPage Today, Bano explained that her group conducted the study "because there is a lot of inconsistency in the literature about the association between thyroid function and distinct atherosclerosis outcomes. Because of its progressive nature, atherosclerosis offers unique opportunities for timely detection and therefore the identification of additional modifiable risk factors for atherosclerosis is of major importance.
Bano's group examined data on 9,231 people (mean age 65; 57% female), who were part of the Rotterdam Study. All participants had data available on thyroid-stimulating hormone levels, free thyroxine levels, and atherosclerotic cardiovascular morbidity and mortality.
They explored the association between thyroid function and subclinical atherosclerosis, atherosclerotic events (fatal and nonfatal coronary heart disease or stroke) and atherosclerotic mortality (death from coronary heart disease, cerebrovascular or other atherosclerotic disease).
Using multivariable-adjusted Cox proportional and logistic regression models, they estimated hazard ratios and odds ratios, respectively, accounting for age, gender, smoking, alcohol intake, BMI, total cholesterol, triglycerides, systolic blood pressure, diabetes, and usage of antihypertensive and lipid-lowering medications.
Bano's group found that over a median follow-up of 8.8 years (interquartile range 4.5-11.8 years), there were 580 atherosclerotic cardiovascular deaths and 1130 first-time hard atherosclerotic cardiovascular events.
The risk of atherosclerotic cardiovascular mortality increased with higher free thyroxine levels and lower thyroid-stimulating hormone levels, predominantly among participants with prevalent atherosclerotic cardiovascular disease (HR 5.76, 95% CI 2.79-11.89 and HR 0.81, 95%CI 0.69-0.95 for TSH, respectively).
The researchers also reported that higher free thyroxine levels were associated with a higher risk of first-time hard atherosclerotic cardiovascular events (HR 1.87, 95% CI 1.34-2.59). Additionally, they found that free thyroxine levels were positively associated with having a high CAC score (OR 2.28, 95% CI 1.30-4.03). Results were similar even after restricting the analyses to participants with thyroid function within reference ranges, she added.
Bano concluded that the study might have potential implications for the prevention of morbidity and mortality, "For example, free thyroxine level measurements can help identify people at risk for atherosclerosis. Also, the study highlights the importance of identifying modifiable mediators that link thyroid function to atherosclerosis."
However, she also noted a need for further research to replicate the findings and investigate potential implications.
"I think that future studies should replicate our findings with the same research question conducted in other similar populations," she told MedPage Today. "And in case it is consistent, another step is to look at younger ages, people younger than 45, because our population includes only middle-aged and elderly people. Another interesting thing could be to look at other ethnicities."