Thyroid disease tied to cardiovascular risk

Researchers uncertain if subclinical thyroid disease treatment would subsequently reduce cardiovascular disease risk.

Patients with subclinical thyroid disease may be at an increased risk of developing cardiovascular complications.

Although more information is still needed about the association between thyroid disease and cardiovascular risk, Jeffrey Henderson, MD, from the Black Hills Center for American Indian Health in Rapid City, S.D., said hypothyroidism may be a predictor for CVD. Henderson spoke at the American Heart Association’s 46th Annual Conference on Cardiovascular Disease Epidemiology and Prevention, held recently in Phoenix.

Henderson’s research was part of the Strong Heart Study, an ongoing trial examining cardiovascular risk in American Indian populations. The findings regarding an association between thyroid disease and cardiovascular risk were based on the second and third phases of the Strong Heart Study.

Examining CVD risk

In each phase of the Strong Heart Study, participating patients were given a clinical exam. Patients who had been free of CVD at the second phase were recruited for the third phase of the study; this included 2,728 patients.

Patients who experienced coronary complications during follow-up or had CVD at the time of the third phase were grouped into the “cases” category. Healthy patients were grouped into the “control” category. Henderson said the two groups were matched for age, gender, diabetes status and geography.

The researchers measured levels of thyroid stimulating hormone (TSH) for all patients. They also examined clinical factors such as blood pressure, total cholesterol, triglycerides and insulin sensitivity.

After controlling for several factors – including age, gender and smoking status – the researchers grouped patients into quintiles, based on TSH levels. Patients in the first quintile had the lowest TSH measurements.

The results demonstrated that patients in the fourth and fifth quintiles were significantly more represented in the cases group than in the controls group. “What we found was a fairly strong relationship – almost a dose-responsive relationship – in increasing levels of TSH and the relationship to CHD,” Henderson said.

Treatment

Although this study examined only American Indian patients, it is likely that the results would be similar for the general population, Henderson said. The Strong Heart Study included patients from various American Indian tribes across the United States; no significant differences in the link between high TSH levels and CVD were seen among these various groups.

Henderson said although this study demonstrated that subclinical hypothyroidism is linked to CVD, more information is needed to understand if treatments for thyroid disease will lower a patient’s risk of cardiovascular complications.

“What is not known is if treatment of thyroid disease would subsequently impact CHD or CVD,” Henderson said. “There are no studies that have looked at this and, at this time, it is really not possible to predict.”

Henderson added that the Strong Heart Study researchers will continue to examine this issue. “More research is needed to better link subclinical hypothyroidism with the mechanisms of CHD and CVD,” he said. “We are beginning to look at some of these questions.” – by Jay Lewis

For more information:

• Henderson J. Subclinical hypothyroidism and cardiovascular disease incidence. Presented at the American Heart Association’s 46th Annual Conference on Cardiovascular Disease Epidemiology and Prevention. March 2-4, 2006. Phoenix.