Subclinical Hypothyroidism Linked to Increased Coronary Heart Disease and All-cause Mortality
Because thyroid hormones have a significant effect on the heart, hypothyroidism is often linked to numerous coronary heart disease (CHD) risk factors (eg, hypertension).
In the August 2011 issue of the journal Thyroid, researchers at the Cleveland Clinic Preventive Cardiology clinic published a study on whether hypothyroidism and mild to moderate subclinical hypothyroidism (SCH) were linked to increased mortality in patients at the clinic. Their article was called “Hypothyroidism and moderate subclinical hypothyroidism are associated with increased all-cause mortality independent of coronary heart disease risk factors: a PreCIS database study.”
In the patient population, there were 79 patients with hypothyroidism (TSH: >10 μ U/mL), 178 patients with moderate SCH (TSH: 6.1-10 μ U/mL), 1,218 patients with mild SCH (TSH: 3.1-6.0 μ U/mL), and 4,765 euthyroid patients.
All patients had a thorough evaluation that included demographic and laboratory tests—including TSH and multiple CHD risk factors—and were followed for up to 8 years. Data were entered into the PreCIS database; and the social security death index was queried every month to indentify all-cause mortality. Time to death was classified as the difference between the patient’s first clinic visit until the patient’s date of death.
Findings showed that multiple CHD risk factors (eg, age, male gender, systolic blood pressure, triglycerides, and fibrinogen) were more common in patients with hypothyroidism; and CHD prevalence was more common in patients with hypothyroidism or moderate SCH as evident by a higher prevalence of baseline CHD (p<0.001) and higher Framingham risk scores (p<0.001).1
Compared with the euthyroid group, all-cause mortality was higher in patients with hypothyroidism (25.7%) or patients with moderate SCH (18.0%)—but not in patients with mild SCH.1
It was also noted that higher mortality in these groups was seen in both genders, in patients younger than 65 years old, and in those who were not on thyroid replacement therapy; however, this was not observed in patients older than 65 years old.
A review of this study appeared in the September 2011issue of Clinical Thyroidology. The journal noted that after adjusting for multiple variables (eg, smoking, hypertension, cerebrovascular disease, BMI, triglycerides, glucose, and homocysteine), the hazard ratio for mortality was still considerably increased in the moderate SCH (to 1.61) and hypothyroid groups (to 2.34).1
Researchers concluded that hypothyroidism and moderate—but not mild—SCH are linked to increased CHD prevalence as well as all-cause mortality. The study suggests that patients with moderate (but not mild) SCH and those at high risk for CHD should be treated with thyroid replacement therapy.