For the first time, researchers have linked high levels of thyroid hormone in middle-aged and older people to higher risk for atherosclerosis, a condition in which arteries become clogged up and which is a major cause of heart attacks and strokes. The new study does not say that raised thyroid hormone leads to atherosclerosis, but it does suggest that it could help to identify people at higher risk for the condition.

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The study found a link between thyroid function and clinical and subclinical signs of atherosclerosis - the main cause of heart attack and stroke.

Atherosclerosis is a disease in which plaque builds up on the inside walls of arteries, causing them to thicken and harden.

The plaque consists of fats, waste products from cells, cholesterol, calcium, and a blood-clotting material called fibrin.

As the plaque builds up, it can eventually impede blood flow through the artery and give rise to diseases such as angina (chest pain), coronary heart disease, carotid artery disease, peripheral artery disease, and chronic kidney disease.

Another potential danger is that a piece can break off or a blood clot can form on the plaque. These can block the artery and cause heart attack or stroke.

According to a 2016 statistics report from the American Heart Association, heart disease and stroke were responsible for the most deaths worldwide in 2013, while heart disease, stroke, or another cardiovascular disease were responsible for 1 out every 3 deaths in the United States in that year.

Link between thyroid function and atherosclerosis

Fast facts about atherosclerosis
  • It is normal for arteries to harden somewhat with age.
  • Scientists do not know exactly what causes atherosclerosis.
  • Smoking speeds up atherosclerosis in many major arteries.

Learn more about atherosclerosis

The new study, which was presented at a recent meeting of the Endocrine Society in Orlando, FL, finds that middle-aged and older people with higher levels of a thyroid hormone called free thyroxine are at higher risk for developing atherosclerosis.

Tests for free thyroxine - also known as free T4 (FT4) - are "used to help evaluate thyroid function and diagnose thyroid diseases" such as hyperthyroidism and hypothyroidism.

Lead author Dr. Arjola Bano, of Erasmus University Medical Center in Rotterdam, the Netherlands, says that their large study is the first to look at the link between thyroid function and clinical and subclinical signs of atherosclerosis, and she notes:

"These findings suggest that thyroid hormone measurement can help identify individuals at risk for atherosclerosis and may have future implications for the prevention of atherosclerotic morbidity and mortality."

Dr. Bano and colleagues analyzed data collected over a median follow-up of 8 years on 9,231 people. They were aged 64.7 years on average and were participating in the Rotterdam Study.

Link is independent of known cardiovascular risk factors

The researchers looked for links between thyroid function and subclinical atherosclerosis, as well as between thyroid function and atherosclerotic events and deaths.

The analysis took account of a range of factors that could affect the results, including age, sex, body mass index (BMI), cholesterol, triglycerides, blood pressure, diabetes, alcohol consumption, smoking, and medications for lowering blood pressure and lipids.

During the follow-up, there were 1,130 atherosclerotic events and 580 atherosclerotic deaths in the group.

The analysis revealed that higher levels of FT4 were linked to higher risk of atherosclerotic events and deaths independently of known cardiovascular risk factors.

Analysis also showed that higher FT4 levels were associated with increased risk of subclinical atherosclerosis - a condition in which plaque build-up can be detected but it has not led to cardiovascular events.

The researchers say that while their findings show a link between thyroid function and atherosclerosis, it appears that the connection occurs via yet to be explored pathways or cardiovascular risk factors.

They also note that further studies now need to replicate their findings and investigate any potential implications.

"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 atherosclerosis is of major importance."

Dr. Arjola Bano

Learn how a compound found in red wine might protect against atherosclerosis.