Increased Levels of Thyroid Hormone Associated With Artery Disease and Death

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Highlights:

• Link between thyroid function and atherosclerosis, found from subclinical atherosclerosis to overt disease and death
• Atherosclerosis is a condition where there is plaque formation in arteries; it is an underlying cause for heart attacks and strokes
• The association seems to be independent of known cardiovascular risk factors like age, cholesterol, blood pressure, diabetes, and smoking.

High and high-normal levels of a thyroid hormone called thyroxine or FT4, are associated with artery disease and death in elderly and middle-aged people, was identified in a new research published in Circulation Research, an American Heart Association journal. FT4 or free thyroxine is a hormone produced by the thyroid gland that is responsible for regulating metabolism. Hyperthyroidism and hypothyroidism are thyroid diseases that are caused by increased and decreased levels of circulating free thyroxine respectively.

Atherosclerosis is a disease where there is plaque formation in the arteries. Hardened arteries are a risk factor for heart disease and stroke.

"Coronary heart disease and stroke remain a leading cause of mortality worldwide, despite advances in prevention and treatment; therefore, identifying additional modifiable risk factors for hardened blood vessels is important" says study author Dr. Arjola Bano, M.D., M.Sc., D.Sc., a researcher in internal medicine and epidemiology at Erasmus University in Rotterdam, the Netherlands.

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The Rotterdam Study

The Rotterdam Study involved 9,420 participants (average age 66 percent women) in which researchers analyzed data to determine the link between two types of hormones: thyroid-stimulating hormone and free thyroxine (FT4), and atherosclerosis and death due to coronary heart disease, cerebrovascular disease or other artery-related illness.

It is believed to be the first population-based study that has studied the relationship between thyroid function and atherosclerosis, from subclinical atherosclerosis (early stages of the disease) to overt disease and death.

Asymptomatic atherosclerosis was determined by measuring coronary artery calcification.

There was a range of factors that could affect the results of the analysis were taken into account; these included age, sex, body mass index (BMI), cholesterol, triglycerides, blood pressure, alcohol consumption, diabetes, smoking, and medications for lowering blood pressure and lipids.

The participants were followed for an average of 8.8 years. There was a total of 934 first-time atherosclerosis-related cardiovascular events and 612 atherosclerosis-related cardiovascular deaths.

Participants who had increased FT4 levels had

• Twice the chance of having high levels of coronary artery calcification scores that were considered to be an indicator of subclinical atherosclerosis
• An 87 percent greater risk of suffering an atherosclerosis-related cardiovascular event
• Double the risk of suffering from an atherosclerosis-related cardiovascular death

These findings were independent of the risk factors taken into account. Researchers predict that the connection maybe occurring via unexplored pathways or non-traditional cardiovascular risk factors.

“We expected that thyroid function would influence the risk of developing atherosclerosis by affecting cardiovascular risk factors such as blood pressure. However, our results remained very similar after accounting for several cardiovascular risk factors,” said Arjola Bano. “This suggests that mechanisms other than traditional cardiovascular risk factors may play a role.”

Some limitations of the study were that it did not measure the levels of FT4 over time and the participants were mostly white middle-age adults. Hence, the results may not be applicable to other populations.

Also, further studies should be done to replicate the findings and investigate any potential implications.

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Atherosclerosis

Atherosclerosis occurs when the inner lining of the walls of arteries get covered with plaque that leads to progressive thickening and hardening of the blood vessels. Plaque is usually comprised of fats, waste products from cells, cholesterol, calcium, and a blood-clotting material called fibrin.

Excess plaque formation in the arteries, impedes blood flow through them and gives rise to diseases such as angina (chest pain), coronary heart disease, carotid artery disease, peripheral artery disease, and chronic kidney disease.

The current Rotterdam study findings indicate that thyroid hormone measurement can help identify individuals at risk for atherosclerosis; this may have future implications for the prevention of atherosclerotic morbidity and mortality.

"Future studies should clarify the exact mechanisms that can explain the link between thyroid function and atherosclerosis. This could help to identify potential targets for future preventative strategies," Bano said.

References:

1. People with higher thyroid hormone levels may be at greater risk for atherosclerosis - (https://www.endocrine.org/news-room/current-press-releases/people-with-higher-thyroid-hormone-levels-may-be-at-greater-risk-for-atherosclerosis)
2. What Is Atherosclerosis? - (https://www.nhlbi.nih.gov/health/health-topics/topics/atherosclerosis/)

Source-Medindia