Hypothyroidism is linked to increased risk of coronary heart disease, death
This finding was based on surveys of the cardiac and endocrine health of more than 6,400 patients, all of whom were included in the clinic's Preventive Cardiology Information System Database between 1995 and 2008.
The resulting report appeared in the journal Thyroid.
Hypothyroidism is relatively common, affecting about 5 percent of Americans, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The condition can be caused by autoimmune reactions, congenital malformations, certain medications, inflammation of the thyroid or removal of the gland, the source states.
Regardless of its genesis, hypothyroidism can lead to a number of interrelated symptoms, ranging from fatigue and dry skin to depression, weight gain or elevated cholesterol levels, the NIDDK adds.
This latter two complications are integral to the logic of the new report. After all, individuals who have high cholesterol or excess body mass are more likely to develop CHD.
In the study, scientists began by keeping track of the health data of people admitted to the clinic for CHD or its symptoms. Prominently, the group monitored the thyroid health of all patients and made note of those found to have overt or subclinical hypothyroidism.
Researchers also periodically checked the Social Security Death Master File to determine the cause of mortality for participants who died during the investigation.
After collecting 15 years' worth of information, scientists examined the data to determine if those patients with hypothyroidism shared any risk factors for CHD or had a higher likelihood of death.
The results were plain. Patients found to have hypothyroidism were more likely to display several of the symptoms of CHD, including advanced age, male gender, hypertension, high triglyceride levels and excess fibrinogen in the blood. The latter is a protein that has been linked to inflammation. It is considered a biomarker for the risk of heart disease.
Individuals with hypothyroidism ended up having a higher-than-average risk of death, even those with the moderate subclinical form of the thyroid disease.
During the study, participants with overt hypothyroidism had a 27 percent higher risk of death than those with healthy thyroids. With moderate subclinical hypothyroidism, individuals still had an 18 percent greater mortality rate.
Researchers were unambiguous in their recommendations.
"These observations suggest patients with moderate, but not mild, [subclinical hypothyroidism] and patients at high risk for CHD should be treated with thyroid replacement therapy," the team concluded.
By taking daily doses of thyroxine, people with hypothyroidism can maintain tight control of their condition, according to the NIDDK. Such disease management has the potential to limit the risk of CHD among people with thyroid disease, the study emphasized.
More than 636,000 Americans die of CHD every year, the Centers for Disease Control and Prevention estimates.