Journal Title (Medline/Pubmed accepted abbreviation): Med Sci Sports Exerc
Page numbers: 1809-1818
Summary of Background and Research Design
Background: Hemodialysis of patients with end-stage renal disease (ESRD) may deplete L-carnitine, an antioxidant that also functions in fat metabolism, potentially contributing to increased morbidity, mortality, and reduced quality of life. Although regular exercise is beneficial in patients with ESRD, exercise alters antioxidant status in various tissues and may cause undue oxidative damage. L-carnitine supplementation may reduce tissue oxidative damage following exercise and aid muscle repair and remodeling in patients with receiving hemodialysis.
Hypothesis:L-carnitine supplementation, in hemodialysis patients, will improve 1) exercise performance, and 2) blood redox status both at rest and after exercise.
Subjects:Twelve male hemodialysis patients (mean age, 53.8 years; body mass index [BMI], 26.5 kg/m2) with a history of chronic therapy for at least 1 year and an absence of antioxidant supplementation (vitamin E, statins, etc) participated in the study.
Experimental design:Double-blind, placebo-controlled, counterbalanced, crossover design
Treatments and protocol: Prior to study, patients were taught how to complete a 5-day diet recall questionnaire and had their anthropomorphic profiles measured. Patients received either L-carnitine (20 mg/kg) or placebo intravenously 3 times per week for 8 weeks. Participants performed an exercise test to exhaustion before and after supplementation. During the test, oxygen consumption (VO2), respiratory quotient, heart rate (HR), and time to exhaustion were recorded. Blood samples, collected before and after exercise, were analyzed for carnitine, lactate, malondialdehyde, protein carbonyls, reduced and oxidized glutathione, antioxidant capacity, catalase, and glutathione peroxidase activity.
Summary of research findings:
- Blood carnitine increased proportionately following L-carnitine supplementation at rest and after exercise.
- L-carnitine supplementation:
- Increased time to exhaustion (22%)
- Decreased postexercise lactate (37%), submaximal HR, and respiratory quotient
- Did not affect VO2peak
- L-carnitine supplementation increased:
- Glutathione reduced/oxidized (2.7-fold at rest, 4-fold postexercise)
- Glutathione peroxidase activity (4.5% at rest, 10% postexercise)
- L-carnitine supplementation decreased:
- Malondialdehyde (19% at rest and postexercise)
- Protein carbonyl concentration (27% at rest, 40% postexercise)
Interpretation of findings/Key practice applications:
At baseline, study participants demonstrated severely impaired VO2peak, corresponding to 45% of the respective values of their age-matched control population. Circulating carnitine concentration was positively correlated with strength, fatigue, and exercise tolerance in patients with ESRD. However, this was a small study that did not include women and was limited by the fact that L-carnitine was administered intravenously, as opposed to the typical oral route of ingestion in most people. Nevertheless, these data suggest that short-term, 2-month, L-carnitine supplementation may attenuate resting and exercise-induced oxidative stress responses, enhance antioxidant status, and foster functional performance in patients undergoing chronic hemodialysis.