Association between fatigue, peripheral serotonin, and L-carnitine in hypothyroidism and in chronic fatigue syndrome

Abstract

BackgroundFatigue of unknown origin is a hallmark symptom in chronic fatigue syndrome (CFS) and is also found in 20% of hypothyroidism patients despite appropriate levothyroxine treatment. Here, we suggest that in these disorders, peripheral serotonin levels are low, and elevating them to normal range with L-carnitine is accompanied with reduced fatigue.MethodsWe conducted a retrospective analysis of follow-up clinical data (CFS N=12; hypothyroidism with fatigue N=40) where serum serotonin and fatigue levels were compared before vs. after 7 weeks of oral L-carnitine supplementation.ResultsAfter L-carnitine, serotonin increased (8-fold in CFS, Sig. = 0.002, 6-fold in hypothyroidism, Sig. < 0.001) whereas fatigue decreased (2-fold in both CFS and hypothyroidism, Sig. = 0.002 for CFS, Sig. < 0.001 for hypothyroidism). There was a negative correlation between serotonin level and fatigue (for CFS, rho = -0.49 before and -0.67 after L-carnitine; for hypothyroidism, rho = -0.24 before and -0.83 after L-carnitine).ConclusionsThese findings suggest a new link between low peripheral serotonin, L-carnitine, and fatigue.

Is the acquired hypothyroidism a risk factor for developing psychiatric disorders?

“…More specific studies have shown that 5-HT is reduced in brain regions implicated in depression, such as the cerebral cortex ( 68 ), hippocampus ( 63 , 69 ), prefrontal cortex ( 63 , 69 ), and dorsal raphe nucleus ( 65 ), in adult rodents with hypothyroidism. Similarly, clinical evidence has demonstrated that patients with acquired hypothyroidism (without L-T 4 treatment) exhibit lower platelet 5-HT concentrations ( 72 ); this deficiency is also observed in serum samples from hypothyroid patients receiving L-T 4 treatment ( 73 ). Additionally, patients with acquired hypothyroidism have reduced central 5-HT activity, as evaluated by the response to dexfenfluramine ( 74 , 75 ).…”