Effect of 6 weeks of n-3 fatty-acid supplementation on oxidative stress in judo athletes
 
 
Journal Title (Medline/Pubmed accepted abbreviation): J Phys Act Health
Year: 2010
Volume:
Number:
Page numbers: 1-11
doi (if applicable):

Summary of Background and Research Design

Background:Strenuous exercise may induce oxidative stress partially through raising body temperature, which increases the production of reactive free-radicals. Oxidative stress results when the level of reactive oxygen and nitrogen free-radicals increases past the point of the body’s ability to reduce/detoxify the reactive species. Reactive free-radicals cause damage to cellular components and may contribute to muscle fatigue through DNA or protein damage, lipid peroxidation, and/or stimulation of proinflammatory cytokine release. Among the lipids, polyunsaturated fatty acids (PUFAs) are very susceptible to free-radical oxidation, and their peroxidation may be assessed by measurement of malondialdehyde (MDA) levels in blood. Antioxidants to reduce free-radicals are present in tissues, and supplementation may ameliorate the effects of oxidative stress on muscles. Supplementation with very-long-chain n-3 PUFAs (n-3 LCPUFAs; eg, eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) has also been shown to decrease resting oxidative stress and inflammatory biomarker levels; however, reports on the effects of n-3 LCPUFAs on exercise-induced oxidative stress are conflicting.

Hypothesis/purpose of study:Assess the effects of EPA and DHA supplementation on resting and exercise-induced lipid peroxidation and oxidative stress in exercise-trained judo athletes.

Subjects:20 male national-level judo competitors who had been practicing for a mean of 15 years and trained 9 hours/week. Judoists were randomized to placebo (age, 22.3 ± 1.4 yr; height, 172.4 ± 3.8 cm; weight, 74.0 ± 4.8 kg; body mass index, 24.6 ± 0.7 kg/m2; percentage body fat, 17.2% ± 2.0%) or to EPA + DHA (n-3 LCPUFAs; age, 22.8 ± 1.4 yr; height, 172.2 ± 2.4 cm; weight, 77.8 ± 5.8 kg; body mass index, 23.6 ± 0.7 kg/m2; percentage body fat, 17.9% ± 2.5%).

Experimental design: Randomized, double-blind, placebo-controlled study.

Treatments and protocol: Data were collected at rest and after a 10-minute judo session before (T1 and T2) and after (T3 and T4) 6 weeks of supplementation with EPA (600 mg/day) and DHA (400 mg/day). Weight, height, and body mass (4 skinfold thickness) were measured. Food diaries were completed for 7 days preceding the baseline and supplementation assessments. Blood samples were collected for triglyceride, lipid peroxidation and antioxidant status, glucose, and insulin measurements. Measures of lipid peroxidation were: maximum amount of conjugated dienes (CDmax), change in maximum rate of oxidation (Rmax), length of lag phase (Lp), and malondialdehyde (MDA). Measures of antioxidant status included glutathione peroxidate (Gpx), retinol, and a-tocopherol. The authors also measured nitrates, which were used as a biomarker of nitric oxide (NO) production (indicator of reactive nitrogen species).

Summary of research findings:
  • Compliance with supplementation was 98% for placebo and 93% for the n-3 LCPUFA group.
  • Dietary intake was not different between the treatment groups.
  • Insulin, glucose, and free fatty acids were not affected by treatment or time, only by exercise.
  • There was a significant supplement × time interaction (P <.01) for plasma triglycerides, with lower mean values in the n-3LCPUFA group vs placebo at T3 and T4.
  • There were significant supplement × time interactions for MDA and Rmax (P =.03 and P =.04, respectively), with the highest values generally observed at T4 for n-3 LCPUFA vs placebo.
  • There were significant supplement X time X exercise interactions for CDmax, Rmax, MDA, and NO biomarkers (P <.05 in each case), again with the highest values generally at T4 for n-3 LCPUFA vs placebo.
  • There were no significant effects for retinol or a-tocopherol, and only exercise main effects (increases) observed for Gpx.
  • There were several exercise main effects (increases) for variables such as CDmax, Rmax, and biomarkers of NO.

Interpretation of findings/Key practice applications:

In this study, supplementation with n-3 LCPUFA s did not ameliorate exercise-induced oxidative stress in exercise-trained male athletes. In fact, the opposite occurred, with increases in oxidative parameters after n-3 LCPUFA supplementation compared with placebo. Although beneficial effects have been noted in animal studies, these studies were performed at high doses that were not comparable to those administered to humans. Clinical studies have yielded conflicting results and suggest that the level of oxidative stress influences the actions of n-3 LCPUFAs. Adding antioxidants to n-3 LCPUFAs may counteract their potentially negative effects at high oxidative stress levels (eg, exercise). Further research is necessary to establish any effects of n-3 LCPUFAs, alone or in combination with antioxidants, on oxidative stress. The lowering of plasma triglycerides by the
n-3 LCPUFA was consistent with previous studies.
 
A key factor to take into consideration regarding the results of this study is that the clinical significance of the alterations in these biomarkers of oxidative stress is not known. Clearly, the health benefits of regular physical activity have been well established and the judo exercise itself caused increases in some markers of oxidative stress. In addition, the demonstrated clinical benefits of n-3 LCPUFA for lipid lowering and anticoagulant effects should be balanced against the potential adverse effects on oxidative stress markers observed in this study.
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