(HealthDay News) – Subclinical hyperthyroidism is associated with increased risk of coronary heart disease (CHD) morbidity and mortality; and treatment with levothyroxine for subclinical hypothyroidism is associated with fewer ischemic heart disease (IHD) events in patients aged 40–70 years, according to two studies published online April 23 in the Archives of Internal Medicine.

To investigate the association between subclinical hyperthyroidism and the risks of total and CHD mortality, CHD events, and atrial fibrillation, Tinh-Hai Collet, MD, from the University of Lausanne in Switzerland, and colleagues reviewed data from 10 cohorts involving 52,674 participants, 2,188 of whom had subclinical hyperthyroidism. The researchers found that subclinical hyperthyroidism correlated with an increased risk of total mortality (hazard ratio [HR], 1.24; 95% CI, 1.06–1.46), CHD mortality (HR, 1.29; 95% CI, 1.02–1.62), CHD events (HR, 1.21; 95% CI, 0.99–1.46), and atrial fibrillation (HR, 1.68; 95% CI, 1.16–2.43). The associations did not differ by age, gender, or preexisting cardiovascular disease, and remained after further adjustment for cardiovascular risk factors.

Salman Razvi, MD, from Newcastle University in the United Kingdom, and colleagues investigated whether treatment of subclinical hypothyroidism with levothyroxine was associated with IHD morbidity and mortality in 3,093 younger (aged 40–70 years) and 1,642 older (>70) individuals. There were 68 incidents in 1,634 younger treated individuals vs. 97 events in 1,459 untreated individuals (4.2% vs. 6.6%; adjusted HR, 0.61; 95% CI, 0.39–0.95). In older individuals, there were 104 events in 819 treated patients vs. 88 events in 823 untreated patients (12.7% vs. 10.7%; adjusted HR, 0.99; 95% CI, 0.59–1.33).

“Treatment of subclinical hypothyroidism with levothyroxine was associated with fewer IHD events in younger individuals, but this was not evident in older people,” Razvi and colleagues conclude.

One author from the second study disclosed financial ties to Merck Serono, which manufactures levothyroxine.

Abstract – Collet
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Abstract – Razvi
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