Purpose: The role of thyroxine replacement in subclinical hypothyroidism remains unclear. We performed a 6-month randomized, double-blind, placebo-controlled trial to evaluate the effects of thyroxine treatment for mild subclinical hypothyroidism, defined as a serum thyroid-stimulating hormone level between 5 to 10 microU/mL with a normal serum free thyroxine level (0.8-16 ng/dL).
Subjects and methods: We randomly assigned 40 women with mild subclinical hypothyroidism who had presented to their family practitioners to either thyroxine treatment (n = 23; 50 to 100 microg daily) or placebo (n = 17). Health-related quality of life (Hospital Anxiety and Depression scale, 30-item General Health Questionnaire), fasting lipid profiles, body weight, and resting energy expenditure were measured at baseline and 6 months.
Results: The most common presenting symptoms were fatigue (n = 33 [83%]) and weight gain (n = 32 [80%]). At presentation, 20 women (50%) had elevated anxiety scores and 22 (56%) had elevated scores on the General Health Questionnaire. Thirty-five women completed the study. There were no significant differences in the changes from baseline to 6 months between women in the thyroxine group and the placebo group for any of the metabolic, lipid, or anthropometric variables measured, expressed as the mean change in the thyroxine group minus the mean change in the placebo group: body mass index, -0.3 kg/m(2) (95% confidence interval [CI]: -0.9 to 0.4 kg/m(2)); resting energy expenditure, -0.2 kcal/kg/24 h (95% CI: -1.3 to 1.0 kcal/kg/24 h); and low-density lipoprotein cholesterol, -4 mg/dL (95% CI: -23 to 15 mg/dL). There was a significant worsening in anxiety scores in the thyroxine group (scores increased in 8 of 20 women and were unchanged in 2 of 20) compared with the placebo group (scores increased in 1 of 14 women and were unchanged in 6 of 14; P = 0.03). CONCLUSIONS; We observed no clinically relevant benefits from 6 months of thyroxine treatment in women with mild subclinical hypothyroidism.