A study published in Archives of Internal Medicine reveals that subclinical hyperthyroidism (SCH) may be linked to a greater risk of total mortality, coronary heart disease (CHD) death, as well as incident atrial fibrillation (AF). The findings also indicate that the risk of AF and CHD death is higher when thyrotropin levels are below 0.10 mIU/L.
SCH is a relatively common condition defined by low thyrotropin levels with normal concentrations of free thyroxine (FT 4 ) and triiodothyronine (T 3 ). Earlier studies have suggested that SCH, which is often asymptomatic, is linked to cardiovascular system effects, increased heart rate, incident AF, as well as CHD. However, these prospective studies have produced conflicting results and conclusions from study-level meta-analyses have been contradicting.
The researchers said:
"Although no large randomized controlled trials have examined the effects of treating subclinical hyperthyroidism on clinically relevant outcomes, a consensus statement and recent guidelines advocate treatment of subclinical hyperthyroidism, particularly when thyrotropin level is lower than 0.10 mIU/L, to avoid long-term complications."
Tinh-Hai Collet, M.D., of the University of Lausanne, Switzerland, and colleagues analyzed data from 10 prospective cohorts including 52,674 participants. 2,188 (4.2%) of the participants had endogenous SCH. The median age of study participants was 59 years old and 58.5% of them were women.
The researchers found that during follow-up, 785 participants had incident AF, 3,653 had CHD events, and 8,527 died (including 1,896 from CHD). In studies that adjusted for age and sex, the team found that SCH, vs. normal thyroid function (euthyroidism), was linked to increased risk of total mortality (hazard ratio [HR] 1.24), incident AF (HR, 1.68), CHD mortality (HR, 1.29), and CHD events (HR, 1.21).
Results from the study indicated that incident AF, as well as CHD mortality (but no other outcomes), were "significantly greater" in study participants with lower thyrotropin levels.
The researchers conclude:
"Our study is observational, and as such cannot address whether the risks associated with subclinical hyperthyroidism are lowered by treatment. A large randomized controlled trial with relevant clinical outcomes will be required to demonstrate whether these risks are altered by therapy."
Commenting on the study, Kenneth D. Burman, M.D., of MedStar Washington Hospital Center and Georgetown University, Washington, D.C., explains:
"In conclusion, the study by Collet et al provides important information regarding the importance of recognizing subclinical hyperthyroidism in anticipation of decreasing cardiac and osseous risks, although definitive prospective long-term, controlled studies proving the benefits of treatment in various age groups have not been performed."
"Until further data are available, the relationship between subclinical hyperthyroidism and increased mortality, CHD mortality and atrial fibrillation presently provides sufficient evidence to consider treatment of subclinical hyperthyroidism, especially in elderly patients with cardiac risks, hyperthyroid symptoms or osteoporosis."
Written By Grace Rattue