Even a slightly overactive thyroid leads to a higher mortality rate and risk of atrial fibrillation, a large-scale study suggests.
A study published Tuesday in the Archives of Internal Medicine (online) found patients with subclinical hyperthyroidism were 24% more likely to die over the study period than someone with normal thyroid function.
For CHD mortality the likelihood was increased by 29%, and the likelihood of AF was increased by 68%.
The research, which pooled data from 10 different studies, defined subclinical hyperthyroidism as a thyrotropin (TSH) level below 0.45 mIU/L, in combination with normal concentrations of free thyroxine (FT4) and triiodothyronine (T3).
The risks of coronary heart disease mortality and incident AF were even greater in patients with thyrotropin levels below 0.10 mIU/L, the authors noted.
In an accompanying editorial, US endocrinologist Dr Kenneth Burman called on doctors to take the condition seriously. Treatment options included radioactive iodine, anti-thyroid agents and surgery, he said.
“Until further data are available, the relationship between subclinical hyperthyroidism and increased mortality, CHD mortality and AF presently provides sufficient evidence to consider treatment … especially in elderly patients with cardiac risks, hyperthyroid symptoms or osteoporosis," Dr Burman wrote.
The study pooled data on 52,000 patients from 10 cohorts in Australia, Europe, Brazil and the US. Patients were followed up for periods varying from one to 20 years.
The authors attributed their findings to the systemic effects of thyroid hormones, such as altered cardiac function or arrhythmia. The risks remained elevated after adjustment for age, sex and pre-existing cardiovascular disease.
They noted however that trials had yet to demonstrate that treating subclinical hyperthyroidism actually prevented adverse outcomes.
Archives of Internal Medicine 2012; online.