Subclinical hyperthyroidism associated with higher risk of mortality, coronary heart disease and atrial fibrillation, reveals report published in Archives of Internal Medicine. Subclinical hyperthyroidism is defined by low thyrotropin levels with normal concentrations of free thyroxine (FT 4 ) and triiodothyronine (T 3 ). The condition has been associated with cardiovascular system effects, including an increased heart rate, and observational studies have suggested an association with CHD and incident AF, the authors write in their study background. However, they note that results from prospective cohort studies have been conflicting and study-level meta-analyses have reached contradictory conclusions. "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," the authors comment. Tinh-Hai Collet, M.D., of the University of Lausanne, Switzerland, and colleagues searched the medical literature and analyzed individual data pooled data from 10 prospective cohorts with a total of 52,674 participants with a median age of 59 years and 58.5 percent of them women. Of the participants, 2,188 (4.2 percent) had endogenous subclinical hyperthyroidism. During follow-up, 8,527 participants died (including 1,896 from CHD), 3,653 had CHD events and 785 had incident AF. In age- and sex-adjusted analyses, subclinical hyperthyroidism, compared with euthyroidism (normal thyroid function) was associated with increased risk of total mortality (hazard ratio [HR] 1.24), CHD mortality (HR, 1.29), CHD events (HR, 1.21) and incident AF (HR, 1.68). CHD mortality and incident AF (but not other outcomes) were "significantly greater" in participants with lower thyrotropin levels, according to the study results. "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," the authors conclude. (Arch Intern Med. Published online April 23, 2012. doi:10.1001/archinternmed.2012.402. Available pre-embargo to the media at www.jamamedia.org.) Editor's Note: This study was supported by a grant from the Swiss National Science Foundation. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc. Invited Commentary: Clinical Importance of Subclinical Hyperthyroidism In an invited commentary, Kenneth D. Burman, M.D., of MedStar Washington Hospital Center and Georgetown University, Washington, D.C., writes: "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." 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