. Scientific Frontline: Mild thyroid disorders can cause serious heart problems

Monday, October 24, 2022

Mild thyroid disorders can cause serious heart problems

Johannes W. Dietrich works in the section diabetology, endocrinology and metabolism of Medical Clinic I in the RUB Clinic St. Josef Hospital.
Credit: Curtesy of Johannes W. Dietrich

A systematic evaluation of 32 studies with 1.3 million participants reveals new relationships.

It has been known for more than 200 years that severe over functions of the thyroid gland can lead to disturbances in the heart rhythm and thus to sudden cardiac death. So far, it has been unclear what risk is associated with only slight over- or under-functions. A systematic evaluation of 32 studies with 1.3 million participants shows that even slight deviations in thyroid function can increase the risk of serious cardiovascular diseases. "This puts our understanding of the interaction between the thyroid and the heart on a new footing and shows the way to personalized prevention," said private lecturer Dr. Johannes Dietrich from the medical clinic in St. Josef Hospital, Clinic of the Ruhr University Bochum (RUB). The researchers worked in the journal Frontiers in Cardiovascular Medicine.

For the work, the cardiac and hormone researchers of the RUB cooperated with the Tan Tock Seng Hospital, the Lee Kong Chian School of Medicine and the Duke-NUS Medical School in Singapore.

How to deal with mild thyroid disorders?

Melvin Khee Shing Leow works in the endocrinology department of Tan Tock Seng Hospital in Singapore.
Credit: Curtesy of Melvin Khee Shing

Manifest thyroid dysfunction is now considered an established risk factor for serious diseases of the cardiovascular system. However, the situation with mild thyroid dysfunction has so far remained unclear. "While in some studies minimal increases in thyroid hormones, even normal concentrations within the reference range for healthy people, were associated with an increased risk of sudden cardiac death, other studies could not be clearly linked," explains Johannes Dietrich. It was therefore controversial how to deal with early over- and under-functions of the thyroid gland - so-called latent hyper- and hypothyroidism.

In order to gain a more overview, the international team created a systematic review of 32 studies on this topic. In a summarized statistical assessment with a downstream meta-analysis, the researchers found that both latent hypothyroidism and latent hyperthyroidism predict the risk of cardiac death. In addition, the concentrations of the free thyroid hormone T4 (FT4) were related to the likelihood of cardiac death and other cardiovascular events.

Two different patterns

Patrick Müller works at the Vest Clinic, an academic teaching hospital of the Medical Faculty of the RUB .
Credit: Curtesy of Patrick Müller

"The results speak for a cardiovascular risk that increases continuously with the FT4 concentration, but for a complex U-shaped connection with the concentration of the control hormone TSH," explains Johannes Dietrich. This constellation is probably based on two different patterns of the thyroid-mediated cardiac arrhythmias.

In one form ("dyshomöostatic type") there is a thyroid disease that leads directly to a high concentration of thyroid hormones and above it increases the risk of cardiovascular disease. In the other form ("allostatic type"), the setpoint of the control loop between the pituitary gland and the thyroid is increased by genetic factors, chronic stress and psychological stress, so that rhythm disturbances are also favored by the indirectly increased FT4 concentration.

Provide and treat individually

"

Illustration thyroid
Credit: Curtesy of the research team

The results of the study could lead to a personalized prevention strategy for cardiovascular diseases," the authors said. “In addition, if the cardiac arrhythmias already exist, thyroid function could serve as a biomarker for the respective development mechanism in the future and help to select an individually optimized drug therapy."

Source/Credit: Ruhr University Bochum

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