Hypothyroid patients experience
fatigue-related symptoms despite adequate
thyroid hormone replacement.
Thyroid hormone plays an essential role in
carnitine-dependent
fatty acid import and oxidation. We investigated the effects of
L-carnitine supplementation on
fatigue in patients with
hypothyroidism. In total, 60 patients (age 50.0 ± 9.2 years, 3 males, 57 females) who still experienced
fatigue (
fatigue severity scale [FSS] score ≥ 36) were given
L-carnitine (
n = 30, 990 mg
L-carnitine twice daily) or placebo (
n = 30) for 12 weeks. After 12 weeks, although neither the FSS score nor the physical
fatigue score (PFS) changed significantly, the
mental fatigue score (MFS) was significantly decreased by treatment with
L-carnitine compared with placebo (from 4.5 ± 1.9 to 3.9 ± 1.5 vs. from 4.2 ± 1.8 to 4.6 ± 1.6, respectively; P < 0.01). In the
L-carnitine group, 75.0%, 53.6%, and 50.0% of patients showed improvement in the FSS score, PFS, and MFS, respectively, but only 20.0%, 24.0%, and 24.0%, respectively, did so in the placebo group (all P < 0.05). Both the PFS and MFS were significantly improved in patients younger than 50 years and those with free T3 ≥ 4.0 pg/mL by treatment with
L-carnitine compared with placebo. Additionally, the MFS was significantly improved in patients taking
thyroid hormone after
thyroid cancer surgery. These results suggest that
L-carnitine supplementation may be useful in alleviating
fatigue symptoms in hypothyroid patients, especially in those younger than 50 years and those who have
hypothyroidism after
thyroidectomy for
thyroid cancer (ClinicalTrials.gov: NCT01769157).