Treating subclinical hypothyroidism with levothyroxine was found to decrease the rate of ischemic heart disease in patients aged 40-70 years, the first evidence ever to be published regarding the benefit of treatment on "hard" clinical outcomes, according to a report published online April 23 in Archives of Internal Medicine
In a review of the medical records of 4,735 patients across the United Kingdom, levothyroxine therapy reduced all-cause mortality and the number of ischemic heart disease events in adults up to 70 years of age, but did not benefit those older than 70, said Dr. Salman Razvi of the Institutes of Human Genetics, Newcastle (U.K.) University, and his associates.
Subclinical hypothyroidism has been believed to predispose patients to cardiovascular disease for decades, but no adequately powered randomized controlled intervention trials have been performed to determine whether treatment of the condition actually improves the risk for ischemic heart disease. Nevertheless, many patients with subclinical hypothyroidism are treated with levothyroxine for symptoms of the condition as well as for the perceived amelioration of CV risk factors such as dyslipidemia, the investigators said.
They examined the issue using data from the General Practitioner Research Database, which contains the longitudinal medical records of a representative sample of more than 10 million British patients (about 16% of the U.K. population). The researchers identified 4,735 adults diagnosed as having subclinical hypothyroidism in 2001 and tracked their records for a median of 8 years for the development of cardiovascular morbidity and mortality.
The study cohort was divided into younger and older groups, with 3,093 subjects aged 40-70 years and 1,642 subjects aged over 70 years. Previous studies have established that subclinical hypothyroidism does not have the same adverse cardiovascular effects in elderly patients as in younger patients, and may even be cardioprotective, Dr. Razvi and his colleagues noted.
During follow-up, both fatal and nonfatal ischemic heart disease events occurred in 165 patients in the younger group (5.3%) and 192 in the older group (11.7%).
In the younger group, the number of such events was 39% lower among patients taking levothyroxine than in untreated patients, a significant difference. All-cause mortality also was lower in the treated younger patients, by 64% ( Arch. Int. Med. 2012 April 23 [doi:10.1001/archinternmed.2012.1159 ].
However, in the older patients, there were no significant differences between treated and untreated patients in the rate of ischemic heart disease events or all-cause mortality.
In addition, the incidence of atrial fibrillation showed no association with treatment of subclinical hypothyroidism in either study group.
"Our data suggest that physicians can be reassured that levothyroxine treatment of subclinical hypothyroidism in patients aged 40-70 years is not harmful and may be associated with modestly improved medium-term health outcomes," the investigators said.
They added that their findings "may provide the best evidence about the management of subclinical hypotension for some time," given that no prospective randomized controlled trials of the issue have yet begun.
This study was funded in part by the Medical Research Council. One of Dr. Razvi’s associates reported receiving speakers’ fees from Merck Serono, and no other financial conflicts of interest were reported.