Glasgow, Scotland—As many as 18% of adults aged 65 years and older—more likely women than men—have subclinical hypothyroidism, which is defined as an elevated thyrotropin level and a free thyroxine level within the reference range.

Whether the condition should be treated with thyroid hormone therapy, however, is a matter of continuing debate, according to a recent report in the New England Journal of Medicine.

 “The use of levothyroxine to treat subclinical hypothyroidism is controversial,” note the authors from the University of Glasgow–led TRUST study group. “We aimed to determine whether levothyroxine provided clinical benefits in older persons with this condition.”

To do that, the investigators conducted a double-blind, randomized, placebo-controlled, parallel-group trial. Participating were 737 adults—with an average age of 74.4 years, and slightly more women than men—who had subclinical hypothyroidism, i.e., a thyrotropin level of 4.60 to 19.99 mIU per liter and free thyroxine level within the reference range.

About half the patients received levothyroxine at a starting dose of 50 mcg daily, or 25 mcg if the body weight was less than 50 kg or the patient had coronary heart disease, with dose adjustment according to the thyrotropin level. The remaining patients were assigned to receive placebo with mock dose adjustment.

Researchers were looking for a change in the Hypothyroid Symptoms score and Tiredness score on a thyroid-related quality-of-life questionnaire after 1 year.

Background information in the articles points out that thyroid hormones can have multiple effects, since they act as an essential regulatory factor in a variety of physiological systems—vascular, heart, brain, skeletal, and muscle.

“Tiredness is the most important symptom of overt hypothyroidism, but most patients with subclinical hypothyroidism have no symptoms or have nonspecific symptoms,” study authors write. “There is a convincing epidemiologic association with subsequent coronary heart disease.”

Past trials, meanwhile, offered only limited evidence regarding the possible benefits and risks of treatment.

Results of this study indicate no differences in the mean change at 1 year in the Hypothyroid Symptoms score (0.2±15.3 in the placebo group and 0.2±14.4 in the levothyroxine group) or the Tiredness score (3.2±17.7 and 3.8±18.4, respectively). Furthermore, the report notes that no beneficial effects of levothyroxine were detected when looking at secondary-outcome measures.

“Levothyroxine provided no apparent benefits in older persons with subclinical hypothyroidism,” the study concludes.

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