Inter-individual variability in redox and performance responses after antioxidant supplementation: A randomized double blind crossover study.

AIM: We aimed to investigate the inter-individual variability in redox and physiological responses of antioxidant-deficient subjects after antioxidant supplementation. METHODS: Two hundred individuals were sorted by plasma vitamin C levels. A low vitamin C group (n = 22) and a control group (n = 22) were compared in terms of oxidative stress and performance. Subsequently, the low vitamin C group received for 30 days vitamin C (1 g) or placebo, in randomized, double-blind, crossover fashion, and the effects were examined through a mixed-effects model, while individual responses were calculated. RESULTS: The low vitamin C group exhibited lower vitamin C (-25 µmol/L; 95%CI[-31.7, -18.3]; p < 0.001), higher F2 -isoprostanes (+17.1 pg/mL; 95%CI[6.5, 27.7]; p = 0.002), impaired VO2max (-8.2 mL/kg/min; 95%CI[-12.8, -3.6]; p < 0.001) and lower isometric peak torque (-41.5 Nm; 95%CI[-61.8, -21.2]; p < 0.001) compared to the control group. Regarding antioxidant supplementation, a significant treatment effect was found in vitamin C (+11.6 µmol/L; 95%CI[6.8, 17.1], p < 0.001), F2 -isoprostanes (-13.7 pg/mL; 95%CI[-18.9, -8.4], p < 0.001), VO2max (+5.4 mL/kg/min; 95%CI[2.7, 8.2], p = 0.001) and isometric peak torque (+18.7; 95%CI[11.8, 25.7 Nm], p < 0.001). The standard deviation for individual responses (SDir) was greater than the smallest worthwhile change (SWC) for all variables indicating meaningful inter-individual variability. When a minimal clinically important difference (MCID) was set, inter-individual variability remained for VO2max , but not for isometric peak torque. CONCLUSION: The proportion of response was generally high after supplementation (82.9%-95.3%); however, a few participants did not benefit from the treatment. This underlines the potential need for personalized nutritional interventions in an exercise physiology context.

Free radicals and antioxidants: appealing to magic.

In biology, there are no good or evil molecules. There is limited or no evidence to support the consumption of antioxidants or (super)foods rich in antioxidants, for the intended purpose of an antioxidant effect, because there is risk of interfering with free radicals and deoptimizing the regulation of fundamental processes.

Antioxidant supplementation, redox deficiencies and exercise performance: A falsification design.

The aim of the present study was to validate the idea of personalized redox supplementation by subjecting individuals to targeted and non-targeted antioxidant supplementation schemes. Seventy-three volunteers were screened for plasma vitamin C and erythrocyte glutathione levels. Three groups were formed: i) the "low vitamin C″ group (12 individuals with the lowest vitamin C levels; Low VitC), ii) the "low glutathione" group (12 individuals with the lowest glutathione levels; Low GSH) and iii) a control group (12 individuals with moderate vitamin C and glutathione levels). The three groups received 1 g of vitamin C or 1.2 g of NAC daily for 30 days in a crossover design with a wash-out period of 30 days. Both antioxidant treatments reduced the increased resting systemic oxidative stress levels, assessed via urine F2-isoprostanes, in the Low VitC and Low GSH groups (P < .05). A significant group × time interaction (P < .05) was found for VO2max and isometric peak torque after both treatments, with the Low VitC and Low GSH groups exhibiting improved performance only after the targeted treatment (vitamin C and NAC, respectively). A significant group × time interaction (P < .05) was found for fatigue index after NAC treatment, but not after vitamin C treatment. No interaction was found for the Wingate test after both treatments. Most of the evidence verifies the idea that antioxidant supplementation increases performance when a particular deficiency is reversed. This indicates that the presence of oxidative stress per se does not rationalize the use of antioxidants and emphasizes the need to identify "responsive" phenotypes.

Acute nicotinamide riboside supplementation improves redox homeostasis and exercise performance in old individuals: a double-blind cross-over study.

PURPOSE: Older individuals suffer from low NADH levels. We have previously shown that nicotinamide riboside [NR; a NAD(P)(H) precursor] administration impaired exercise performance in young rats. It has been suggested that supplementation of redox agents exerts ergogenic effect only in deficient individuals. We hypothesized that old individuals would more likely benefit from NR supplementation. We investigated the effect of acute NR supplementation on redox homeostasis and physical performance in young and old individuals. METHODS: Twelve young and twelve old men received NR or placebo in a double-blind cross-over design. Before and 2 h after NR or placebo supplementation, blood and urine samples were collected, while physical performance (VO2max, muscle strength, and fatigue) was assessed after the second blood sample collection. RESULTS: At rest, old individuals exhibited lower erythrocyte NAD(P)H levels, higher urine F2-isoprostanes and lower erythrocyte glutathione levels compared to young (P < 0.05). NR supplementation increased NADH (51% young; 59% old) and NADPH (32% young; 38% old) levels in both groups (P < 0.05), decreased F2-isoprostanes by 18% (P < 0.05), and tended to increase glutathione (P = 0.078) only in the old. NR supplementation did not affect VO2max and concentric peak torque, but improved isometric peak torque by 8% (P = 0.048) and the fatigue index by 15% (P = 0.012) in the old. In contrast, NR supplementation did not exert any redox or physiological effect in the young. CONCLUSIONS: NR supplementation increased NAD(P)H levels, decreased oxidative stress, and improved physical performance only in old subjects, substantiating that redox supplementation may be beneficial only in individuals with antioxidant deficiencies.

Antioxidants in Personalized Nutrition and Exercise.

The present review highlights the idea that antioxidant supplementation can be optimized when tailored to the precise antioxidant status of each individual. A novel methodologic approach involving personalized nutrition, the mechanisms by which antioxidant status regulates human metabolism and performance, and similarities between antioxidants and other nutritional supplements are described. The usefulness of higher-level phenotypes for data-driven personalized treatments is also explained. We conclude that personally tailored antioxidant interventions based on specific antioxidant inadequacies or deficiencies could result in improved exercise performance accompanied by consistent alterations in redox profile.

Beetroot Increases Muscle Performance and Oxygenation During Sustained Isometric Exercise, but Does Not Alter Muscle Oxidative Efficiency and Microvascular Reactivity at Rest.

OBJECTIVE: To examine the effects of beetroot juice (BRJ) on (i) in vivo skeletal muscle O2 consumption (mVO2) and microvascular reactivity at rest and (ii) muscle performance, muscle oxygenation, and mVO2 during sustained isometric handgrip exercise (IHG). METHODS: Sixteen young males consumed, randomly, a nitrate-rich (8.1 mmol BRJnitrate) or nitrate-depleted (BRJplacebo) BRJ. After 2.5 hours, they performed an occlusion-reperfusion maneuver at rest, a 3-minute sustained IHG, and a sustained IHG to exhaustion with arterial occlusion. Changes in muscle oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), microvascular red blood cell content (tHb), and mVO2 were measured using near-infrared spectroscopy. Force output was recorded. RESULTS: During occlusion, the O2Hb decline did not differ between BRJnitrate and BRJplacebo (magnitude: -30.3 ± 1.6 vs. -31.1 ± 1.5 ΔµΜ; slope: -0.107 ± 0.007 vs. -0.111 ± 0.007 µΜ second-1). During reperfusion, all microvascular reactivity indices were not altered after BRJnitrate (e.g., O2Hbslope: 1.584 ± 0.093 vs. 1.556 ± 0.072 µΜ second-1). During the second and third minute of IHG, O2Hb and tHb were higher in BRJnitrate versus BRJplacebo (p < 0.05), and force output was higher during the third minute (10.8 ± 0.7 vs. 9.5 ± 1.2 kg; p < 0.05); HHb did not differ between trials. In IHG with arterial occlusion, BRJnitrate prolonged the time to fatigue (94.1 ± 5.8 vs. 80.1 ± 3.3 seconds; p < 0.01), with no effects on O2Hb decline (O2Hbslope: -0.226 ± 0.015 vs. -0.230 ± 0.026 µΜ s-1) and mVO2 (14.1 ± 1.0 vs. 14.3 ± 1.6 µmol l-1 minute-1). CONCLUSION: Acute BRJ ingestion in moderately trained individuals (i) did not alter in vivo skeletal muscle microvascular reactivity (index of microvascular function at rest) and basal oxidative efficiency, (ii) increased muscle oxygenation during IHG (possibly via enhanced O2 delivery), and (iii) provided ergogenic benefits during sustained IHG with no effects on muscle oxidative efficiency. The ergogenic effects of BRJ appeared independent of its tissue perfusion benefits.

N-acetylcysteine supplementation increases exercise performance and reduces oxidative stress only in individuals with low levels of glutathione.

Most of the evidence indicates that chronic antioxidant supplementation induces negative effects in healthy individuals. However, it is currently unknown whether specific redox deficiencies exist and whether targeted antioxidant interventions in deficient individuals can induce positive effects. We hypothesized that the effectiveness of antioxidant supplements to decrease oxidative stress and promote exercise performance depends on the redox status of the individuals that receive the antioxidant treatment. To this aim, we investigated whether N-acetylcysteine (NAC) supplementation would enhance exercise performance by increasing glutathione concentration and by reducing oxidative stress only in individuals with low resting levels of glutathione. We screened 100 individuals for glutathione levels and formed three groups with low, moderate and high levels (N = 36, 12 per group). After by-passing the regression to the mean artifact, by performing a second glutathione measurement, the individuals were supplemented with NAC (2 × 600mg, twice daily, for 30 days) or placebo using a double-blind cross-over design. We performed three whole-body performance tests (VO2max, time trial and Wingate), measured two systemic oxidative stress biomarkers (F2-isoprostanes and protein carbonyls) and assessed glutathione-dependent redox metabolism in erythrocytes (glutathione, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase and NADPH). The low glutathione group improved after NAC supplementation in VO2max, time trial and Wingate by 13.6%, 15.4% and 11.4%, respectively. Thirty days of NAC supplementation were sufficient to restore baseline glutathione concentration, reduce systemic oxidative stress and improve erythrocyte glutathione metabolism in the low glutathione group. On the contrary, the 30-day supplementation period did not affect performance and redox state of the moderate and high glutathione groups, although few both beneficial and detrimental effects in performance were observed. In conclusion, individuals with low glutathione levels were linked with decreased physical performance, increased oxidative stress and impaired redox metabolism of erythrocytes. NAC supplementation restored both performance and redox homeostasis.

The NAD(+) precursor nicotinamide riboside decreases exercise performance in rats.

BACKGROUND: Nicotinamide adenine dinucleotide (NAD(+)) and its phosphorylated form (NADP(+)) are key molecules in ubiquitous bioenergetic and cellular signaling pathways, regulating cellular metabolism and homeostasis. Thus, supplementation with NAD(+) and NADP(+) precursors emerged as a promising strategy to gain many and multifaceted health benefits. In this proof-of-concept study, we sought to investigate whether chronic nicotinamide riboside administration (an NAD(+) precursor) affects exercise performance. METHODS: Eighteen Wistar rats were equally divided in two groups that received either saline vehicle or nicotinamide riboside at a dose of 300 mg/kg body weight/day for 21 days via gavage. At the end of the 21-day administration protocol, both groups performed an incremental swimming performance test. RESULTS: The nicotinamide riboside group showed a tendency towards worse physical performance by 35 % compared to the control group at the final 10 % load (94 ± 53 s for the nicotinamide riboside group and 145 ± 59 s for the control group; P = 0.071). CONCLUSION: Our results do not confirm the previously reported ergogenic effect of nicotinamide riboside. The potentially negative effect of nicotinamide riboside administration on physical performance may be attributed to the pleiotropic metabolic and redox properties of NAD(+) and NADP(+).

Low vitamin C values are linked with decreased physical performance and increased oxidative stress: reversal by vitamin C supplementation.

PURPOSE: It has been suggested that part of the failure of antioxidant supplementation to reduce oxidative stress and promote health is that it has been administered in humans with normal levels of antioxidants. METHODS: To test this hypothesis, we screened 100 males for vitamin C baseline values in blood. Subsequently, the 10 individuals with the lowest and the 10 with the highest vitamin C values were assigned in two groups. Using a placebo-controlled crossover design, the 20 selected subjects performed aerobic exercise to exhaustion (oxidant stimulus) before and after vitamin C supplementation for 30 days. RESULTS: The low vitamin C group had lower VO2max values than the high vitamin C group. Vitamin C supplementation in this group marginally increased VO2max. Baseline concentration of F2-isoprostanes and protein carbonyls was higher in the low vitamin C group compared to the high vitamin C group. Vitamin C supplementation decreased the baseline concentration of F2-isoprostanes and protein carbonyls in both groups, yet the decrease was greater in the low vitamin C group. Before vitamin C supplementation, F2-isoprostanes and protein carbonyls were increased to a greater extent after exercise in the high vitamin C group compared to the low vitamin C group. Interestingly, after vitamin C supplementation, this difference was narrowed. CONCLUSION: We show for the first time that low vitamin C concentration is linked with decreased physical performance and increased oxidative stress and that vitamin C supplementation decreases oxidative stress and might increase exercise performance only in those with low initial concentration of vitamin C.

Passive smoking reduces and vitamin C increases exercise-induced oxidative stress: does this make passive smoking an anti-oxidant and vitamin C a pro-oxidant stimulus?

The current interpretative framework states that, for a certain experimental treatment (usually a chemical substance) to be classified as "anti-oxidant", it must possess the property of reducing (or even nullifying) exercise-induced oxidative stress. The aim of the study was to compare side by side, in the same experimental setup, redox biomarkers responses to an identical acute eccentric exercise session, before and after chronic passive smoking (considered a pro-oxidant stimulus) or vitamin C supplementation (considered an anti-oxidant stimulus). Twenty men were randomly assigned into either passive smoking or vitamin C group. All participants performed two acute eccentric exercise sessions, one before and one after either exposure to passive smoking or vitamin C supplementation for 12 days. Vitamin C, oxidant biomarkers (F2-isoprostanes and protein carbonyls) and the non-enzymatic antioxidant (glutathione) were measured, before and after passive smoking, vitamin C supplementation or exercise. It was found that chronic exposure to passive smoking increased the level of F2-isoprostanes and decreased the level of glutathione at rest, resulting in minimal increase or absence of oxidative stress after exercise. Conversely, chronic supplementation with vitamin C decreased the level of F2-isoprostanes and increased the level of glutathione at rest, resulting in marked exercise-induced oxidative stress. Contrary to the current scientific consensus, our results show that, when a pro-oxidant stimulus is chronically delivered, it is more likely that oxidative stress induced by subsequent exercise is decreased and not increased. Reversely, it is more likely to find greater exercise-induced oxidative stress after previous exposure to an anti-oxidant stimulus. We believe that the proposed framework will be a useful tool to reach more pragmatic explanations of redox biology phenomena.

Does vitamin C and E supplementation impair the favorable adaptations of regular exercise?

The detrimental outcomes associated with unregulated and excessive production of free radicals remains a physiological concern that has implications to health, medicine and performance. Available evidence suggests that physiological adaptations to exercise training can enhance the body's ability to quench free radicals and circumstantial evidence exists to suggest that key vitamins and nutrients may provide additional support to mitigate the untoward effects associated with increased free radical production. However, controversy has risen regarding the potential outcomes associated with vitamins C and E, two popular antioxidant nutrients. Recent evidence has been put forth suggesting that exogenous administration of these antioxidants may be harmful to performance making interpretations regarding the efficacy of antioxidants challenging. The available studies that employed both animal and human models provided conflicting outcomes regarding the efficacy of vitamin C and E supplementation, at least partly due to methodological differences in assessing oxidative stress and training adaptations. Based on the contradictory evidence regarding the effects of higher intakes of vitamin C and/or E on exercise performance and redox homeostasis, a permanent intake of non-physiological dosages of vitamin C and/or E cannot be recommended to healthy, exercising individuals.

Low-frequency fatigue as an indicator of eccentric exercise-induced muscle injury: the role of vitamin E.

This study investigates whether vitamin E can attenuate eccentric exercise-induced soleus muscle injury as indicated by the amelioration of in situ isometric force decline following a low-frequency fatigue protocol (stimulation at 4 Hz for 5 min) and the ability of the muscle to recover 3 min after the termination of the fatigue protocol. Adult male Wistar rats were divided into vitamin E-supplemented or placebo-supplemented groups studied at rest, immediately post-exercise or 48 h post-exercise. Daily dl-α-tocopheryl acetate intraperitoneal injections of 100 mg/kg body mass for 5 consecutive days prior to exercise doubled its plasma levels. Fatigue index and recovery index expressed as a percentage of the initial tension. FI at 0 h post- and 48 h post-exercise respectively was 88% ± 4.2% and 89% ± 6.8% in the vitamin E groups versus 76% ± 3% and 80% ± 11% in the placebo groups. RI was 99% ± 3.4% and 100% ± 6% in the vitamin E groups versus 82% ± 3.1% and 84% ± 5.9% in the placebo groups. Complementally to the traditionally recorded maximal force, low-frequency fatigue measures may be beneficial for assessing injury-induced decrease in muscle functionality.

The antioxidant effects of a polyphenol-rich grape pomace extract in vitro do not correspond in vivo using exercise as an oxidant stimulus.

Fruits, such as grapes, are essential food of the Mediterranean diet. Grape extracts have potent antioxidant and chemopreventive properties in vitro. Numerous studies have examined the effects of plant extract administration on redox status at rest in animals and humans but their results are controversial. However, there are no studies comparing the in vitro and in vivo effects of plant extracts on oxidative stress using exercise as an oxidant stimulus. Thus, the aim of this study was to investigate whether a polyphenol-rich grape pomace extract of the Vitis vinifera species possesses in vitro antioxidant properties and to examine whether these properties apply in an in vivo model at rest and during exercise. Our findings indicate that the tested extract exhibits potent in vitro antioxidant properties because it scavenges the DPPH(•) and ABTS(•+) radicals and inhibits DNA damage induced by peroxyl and hydroxyl radicals. Administration of the extract in rats generally induced oxidative stress at rest and after exercise whereas exercise performance was not affected. Our findings suggest that the grape pomace extract does not behave with the same way in vitro and in vivo.

No effect of antioxidant supplementation on muscle performance and blood redox status adaptations to eccentric training.

BACKGROUND: It was recently reported that antioxidant supplementation decreases training efficiency and prevents cellular adaptations to chronic exercise. OBJECTIVE: This study aimed to investigate the effects of vitamin C and vitamin E supplementation on muscle performance, blood and muscle redox status biomarkers, and hemolysis in trained and untrained men after acute and chronic exercise. A specific type of exercise was applied (eccentric) to produce long-lasting and extensive changes in redox status biomarkers and to examine more easily the potential effects of antioxidant supplementation. DESIGN: In a double-blinded fashion, men received either a daily oral supplement of vitamin C and vitamin E (n = 14) or placebo (n = 14) for 11 wk (started 4 wk before the pretraining exercise testing and continued until the posttraining exercise testing). After baseline testing, the subjects performed an eccentric exercise session 2 times/wk for 4 wk. Before and after the chronic eccentric exercise, the subjects underwent one session of acute eccentric exercise, physiologic measurements were performed, and blood samples and muscle biopsy samples (from 4 men) were collected. RESULTS: The results failed to support any effect of antioxidant supplementation. Eccentric exercise similarly modified muscle damage and performance, blood redox status biomarkers, and hemolysis in both the supplemented and nonsupplemented groups. This occurred despite the fact that eccentric exercise induced marked changes in muscle damage and performance and in redox status after exercise. CONCLUSION: The complete lack of any effect on the physiologic and biochemical outcome measures used raises questions about the validity of using oral antioxidant supplementation as a redox modulator of muscle and redox status in healthy humans.

Effects of L-carnitine on oxidative stress responses in patients with renal disease.

PURPOSE: Hemodialyzed patients demonstrate elevated oxidative stress and reduced functional status. Exercise induces health benefits, but acute exertion up-regulates oxidative stress responses in patients undergoing hemodialysis. Therefore, the aim of the present study was to examine the effect of L-carnitine supplementation on i) exercise performance and ii) blood redox status both at rest and after exercise. METHODS: Twelve hemodialysis patients received either L-carnitine (20 mg kg(-1) i.v.) or placebo in a double-blind, placebo-controlled, counterbalanced, and crossover design for 8 wk. Participants performed an exercise test to exhaustion before and after supplementation. During the test, V˙O2, respiratory quotient, heart rate, and time to exhaustion were monitored. Blood samples, collected before and after exercise, were analyzed for lactate, malondialdehyde, protein carbonyls, reduced and oxidized glutathione, antioxidant capacity, catalase, and glutathione peroxidase activity. RESULTS: Blood carnitine increased by L-carnitine supplementation proportionately at rest and after exercise. L-carnitine supplementation increased time to fatigue (22%) and decreased postexercise lactate (37%), submaximal heart rate, and respiratory quotient but did not affect V˙O2peak. L-carnitine supplementation increased reduced/oxidized glutathione (2.7-fold at rest, 4-fold postexercise) and glutathione peroxidase activity (4.5% at rest, 10% postexercise) and decreased malondialdehyde (19% at rest and postexercise) and protein carbonyl (27% at rest, 40% postexercise) concentration. CONCLUSIONS: Data suggest that a 2-month L-carnitine supplementation may be effective in attenuating oxidative stress responses, enhancing antioxidant status, and improving performance of patients with end-stage renal disease.

Ergogenic and antioxidant effects of spirulina supplementation in humans.

PURPOSE: Spirulina is a popular nutritional supplement that is accompanied by claiMSS for antioxidant and performance-enhancing effects. Therefore, the aim of the present study was to examine the effect of spirulina supplementation on (i) exercise performance, (ii) substrate metabolism, and (iii) blood redox status both at rest and after exercise. METHODS: Nine moderately trained males took part in a double-blind, placebo-controlled, counterbalanced crossover study. Each subject received either spirulina (6 g x d(-1)) or placebo for 4 wk. Each subject ran on a treadmill at an intensity corresponding to 70%-75% of their VO2max for 2 h and then at 95% VO2max to exhaustion. Exercise performance and respiratory quotient during exercise were measured after both placebo and spirulina supplementation. Blood samples were drawn before, immediately after, and at 1, 24, and 48 h after exercise. Reduced glutathione (GSH), oxidized glutathione (GSSG), GSH/GSSG, thiobarbituric acid-reactive substances (TBARS), protein carbonyls, catalase activity, and total antioxidant capacity (TAC) were determined. RESULTS: Time to fatigue after the 2-h run was significantly longer after spirulina supplementation (2.05 +/- 0.68 vs 2.70 +/- 0.79 min). Ingestion of spirulina significantly decreased carbohydrate oxidation rate by 10.3% and increased fat oxidation rate by 10.9% during the 2-h run compared with the placebo trial. GSH levels were higher after the spirulina supplementation compared with placebo at rest and 24 h after exercise. TBARS levels increased after exercise after placebo but not after spirulina supplementation. Protein carbonyls, catalase, and TAC levels increased similarly immediately after and 1 h after exercise in both groups. CONCLUSIONS: Spirulina supplementation induced a significant increase in exercise performance, fat oxidation, and GSH concentration and attenuated the exercise-induced increase in lipid peroxidation.

Duration of coffee- and exercise-induced changes in the fatty acid profile of human serum.

Prolonged moderate exercise increases the concentration of nonesterified fatty acids (NEFA) and the ratio of unsaturated to saturated (U/S) NEFA in human plasma. The present study examined the duration of these effects and compared them with the effects of coffee ingestion. On separate days and in random order, seven men and six women 1) cycled for 1 h, 2) ingested coffee containing 5 mg caffeine/kg body mass, 3) ingested coffee followed by exercise 1 h later, and 4) did nothing. Blood samples were drawn at 0, 1, 2, 4, 8, 12, and 24 h. Serum was analyzed for lactate, glucose, glycerol, individual NEFA, triacylglycerols, total cholesterol, and HDL cholesterol. Exercise elevated the U/S NEFA and the percentage of oleate, while decreasing the percentages of palmitate and stearate, at the end of exercise but not subsequently. Consumption of coffee triggered a lower lipolytic response with no alterations in U/S or percentages of individual NEFA. These findings may prove useful in discovering mechanisms mediating the effects of exercise training on the fatty acid profile of human tissues.