Hypothyroidism occurs when an underactive thyroid does not produce enough hormones. More than 9.5 million people nationwide have hypothyroidism. People who have thyroid function at the low end of the normal range have subclinical hypothyroidism, also called mild hypothyroidism.
"Our data suggest that mild hypothyroidism may, in fact, be harmful in specific populations, including people with heart failure," said Connie Rhee, MD, MSc, of Brigham and Women's Hospital in Boston. "A 'one-size-fits-all' approach may not be appropriate for assessing risk and determining whether treatment is required for subclinical hypothyroidism."
The retrospective cohort study used data from 14,130 participants in the Third National Health and Nutrition Examination Survey. Using laboratory data, researchers identified 749 participants with hypothyroidism, including 691 with the subclinical form.
Researchers found the condition can have varying impacts on diverse racial and ethnic groups.
"This study is the first to show that African-Americans who have hypothyroidism face a greater risk of death than patients of other racial and ethnic groups," Rhee said. "This elevated risk exists despite the fact that hypothyroidism is less common in the African-American population compared to other groups. More research is needed to confirm these findings and to determine the underlying reasons why hypothyroidism has a differential impact on people of different race and ethnicity."