Researchers from Ruhr University, Bochum have suggested that mild thyroid disorders should be considered a risk factor for major adverse cardiovascular events.
For 200 years, it has been known that serious thyroid disorders such as thyrotoxicosis can cause severe heart problems like cardiac arrhythmia. However, the risk associated with mild thyroid disorders has not been fully understood.
The researchers conducted a systematic review of 32 studies involving 1.3 million participants. The results have shown that even small deviations in thyroid function can increase the risk of serious cardiovascular diseases.
“This puts our understanding of the interaction between the thyroid gland and the heart on a new footing and might pave the way to personalised preventive care,” said associate professor Dr Johannes Dietrich from the Department of Medicine at St Josef Hospital, Clinic of Ruhr University Bochum, Germany.
The researchers published their work in the journal Frontiers in Cardiovascular Medicine.
The researchers at Ruhr University collaborated with clinicians and hormone specialists from Tan Tock Seng Hospital, the Nanyang Technological University’s Lee Kong Chian School of Medicine and Duke-NUS Medical School in Singapore.
The link between thyroid disorders and cardiac death is clear
Overt thyroid disorders are recognised as an established risk factor for major adverse cardiovascular events (MACE). However, the relevance of mild thyroid dysfunction to MACE has been disputed.
“Whereas in some studies, minimal elevations of thyroid hormones and even high-normal concentrations within the reference range for healthy people predicted an increased risk for sudden cardiac death, other studies hadn’t shown such a correlation,” explained Johannes Dietrich.
Prior to this research, the question of whether to treat people with subclinical forms of hyperthyroidism and hypothyroidism was up for debate.
By conducting a fresh systematic review, the international team were able to bolster their understanding of the effects of thyroid disorders on heart disease. Through a pooled statistical evaluation with consecutive meta-analyses, the researchers found that subclinical hypothyroidism and subclinical hyperthyroidism could be used to predict the risk of cardiovascular death.
How to treat thyroid-induced heart disease
The researchers found that serum concentration of the free thyroid hormone FT4 directly correlated to an increased risk of cardiac death and other severe cardiovascular events.
“The results suggest that cardiovascular risk increases continuously with the FT4 concentration, whereas a complex U-shaped risk relationship exists with the concentration of the controlling hormone thyrotropin, i.e., TSH,” explained Johannes Dietrich.
This duality can be explained by the two different patterns of thyroid-mediated arrhythmia. In one form, the dyshomeostatic type, primary thyroid disorders can directly elevate the concentration of thyroid hormones increasing cardiovascular risk.
In the other form, the allostatic type, genetic factors, chronic stress, and psychological strain can increase the set point of the regulatory circuit between the pituitary gland and the thyroid gland. This causes increased FT4 concentration, which leads to arrhythmia.
“The results of this study might pave the way to a personalised preventive strategy for heart outcomes. Moreover, thyroid function might serve as a biomarker for the respective mechanism of origin in patients harbouring cardiac arrhythmia, helping to tailor individually optimised medication regimen,” concluded the authors.