Quercetin supplementation does not attenuate exercise performance and body composition in young female swimmers.

BACKGROUND: Quercetin is a health-enhancing antioxidant bioflavonoid (1-3). This flavonoid occurs in variety of natural fruits and vegetables such as apple, cranberry, onion, broccoli, and teas. Many studies have shown that quercetin has possible positive effects on exercise performance. The aim of this study is the evaluation of effects of quercetin supplementation on VO2max and exercise performance in female athletes.
METHODS: This study was done on 26 young female swimmers. Participants were assigned in to groups and supplemented orally for 8 weeks with either Quercetin (Solaray(®), USA, Inc) or placebo (dextrose). Before and after intervention, athletes performed a continuous graded exercise test (GXT) on an electronically braked cycle ergometer (Lode, The Netherlands) to determine VO2max and time to exhaustion (TTE).
RESULTS: Participants in the quercetin group consumed higher energy and protein and lower carbohydrates and fats. There was no significant differences in VO2max, TTE, lactate, and body fat between pre- and post-supplementation neither in the placebo group nor in the quercetin group.
CONCLUSIONS: It is concluded that quercetin supplementation (1000 g/day) for 8 weeks in female athletes didn't show any significant association with exercise performance.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Dietary supplements are becoming popular among athletes and being used for different reasons. Although supplements are necessary to acquire sufficient amount of essential nutrients such as vitamins and minerals for some athletes especially those using weight loss diet for weight-control sports, Sport supplements are being used for performance enhancement by many athletes.[1] In recent years, a large number of these supplements have been increasingly developed and are being used by athletes. Some of these supplements are classified as drug but most of them are nutritional supplements such as amino acids, protein, vitamins, minerals, and herbals. It has been hypothesized that Quercetin as a phytochemicals which currently exists as a sport supplement may improve physical performance, enhance fitness, and increase energy.[2]

Dietary flavonols like quercetin have healthful properties such as antioxidant, free radical scavenging, anti-inflammatory, anti-carcinogenic and cardio-protective,[3] reduce the risk of chronic diseases and cancer,[4] and decrease the vulnerability to viral infection.[56] Biosynthesis of quercetin motivates by sunlight, so it collects in the external and above ground tissues such as leaves and skin. Flavonoids are found in most of the vegetables and fruits but the main food sources for quercetin are apples, berries, onions, tea, peppers, red grapes, and green vegetables.[7] As a result of quercetin's benefits, it is added to beverages and foods as a nutritional supplement.[8] During exercise, inflammation, oxidative stress, muscle microtrauma and other immune changes occur in human body,[9] and quercetin may have positive effect on these exercise-induced events and could decrease oxidative damage in muscles. Quercetin could be absorbed sufficiently by human subjects[10] and may particularly be accumulated in the liver, heart, thymus, lungs, kidney, testes, and muscle.[5] Studies on human and animal indicated that quercetin supplementation does not have negative effect or adverse symptoms and support the safety of quercetin supplement.[31112]

Recent investigation in mice indicated that quercetin positively affected endurance performance, enhanced mitochondrial biogenesis mRNA and DNA in skeletal muscle and brain.[13] The result of another study demonstrate that quercetin could affect aerobic capacity, skeletal muscle, and endurance performance[14] and may have ergogenic effect in humans. Another study indicated that however in vitro investigation quercetin had antioxidant action, quercetin supplementation didn't protect against exercise-induced inflammation and oxidative stress.[15] Limited data available on the ergogenic effect of quercetin supplementation in humans, these findings are unclear.[8] Finding from a study on adult male subjects demonstrated a small but non-significant raise in some indicators of mitochondrial biogenesis.[16] It has also been assumed that antioxidant properties of quercetin may progress physical performance. As a possible mechanism it has been believed that antioxidant supplementation minimize damage to proteins and membranes of skeletal muscles during exercise, thus limit the harmful effects of raised reactive oxygen generated.[17] However, it is uncertain if antioxidants affect exercise performance.[18] Several studies investigated the effect of quercetin supplementation on VO2max on untrained participants. Although some studies showed small but significant raise in VO2max and cycling time before tiredness,[1619] others found no significant effect.[820] However, few data are available in this regard and these data are controversial. Therefore, we examined the effect of 8 weeks quercetin supplementation (1000 mg per day) in a case control study on VO2max and exercise performance in Iranian young female swimmers.

METHODS

Participants

This case-control study was conducted in Isfahan, Iran in 2011. 26 young female swimmers with convenience non-random sampling procedure volunteered for this investigation. Participants were asked to abstain from exercise 24 h before trial initiation and to maintain their current physical activity and dietary patterns. Participants were randomly assigned to one of two groups: (a) Quercetin (1000 mg/day) n = 14, (b) placebo (1000 m g dextrose per day) n = 12. Cases and controls were matched for age and weight.

Research design

Participants were supplemented orally for 8 weeks with either Quercetin (Solaray®, USA, Inc) or placebo (dextrose). The study was approved by the Ethics Committee (Esfahan Sport Medicine Association, Iran). Supplements were provided in capsules of 500 mg and were administered each day as two divided single doses, with at least 6 h in between ingestions. Thus, daily doses consisted of 1000 mg/day during the study.

Venous blood samples were obtained from all participants between 5:00 and 6:00 p.m., after intensive endurance exercising, at the baseline and after intervention. All measurements were done before the start of the supplementation (Pre) and after the intervention (Post).

Prior to and following the supplementation protocol, participants performed a continuous graded exercise test (GXT) on an electronically braked cycle ergometer (Lode, The Netherlands) to determine VO2max and time to exhaustion (TTE).

For each GXT, the primary power output was set at 30 watts and elevated 30 watts every 2 minutes until the participant couldn't maintain the required power output at a pedaling rate of 70 rpm due to fatigue.

Lactate was analyzed using a Lactometer (Lactate Pro LT-1710, Canada). Body fat percent was measured by Bio Impedance Analyzor (BIA) (JAWON IOI 353, Korea). Dietary analyses were performed using Nutritionist IV software.

Statistical methods

Statistical analyses were conducted using the Statistical Program for the Social Sciences (SPSS version 13, Inc., Chicago, IL) computer software package. Data are presented as means ± standard deviation. The independent t test was used to analyze the differences in performance between the trials. Paired t test was used to analyze before and after test data for each group differences. An alpha level of P < 0.05 was considered statistically significant.

RESULTS

A total of 26 young female swimmers participated in this study. General characteristics and dietary intakes of study participants separately by case and control groups before intervention have been showed in Table 1. There was no difference in age and weight of two groups; however, participants in the quercetin group consumed higher energy and protein and less amount of carbohydrates and fats. Table 2 compared exercise performance indices in quercetin and placebo groups between pre- and post-supplementation. There is no significant differences in VO2max, TTE, lactate, and body fat between pre- and post-supplementation neither in the placebo group nor in the quercetin group.

Table 1

General characteristics and dietary intakes of study participants separately by case and control groups before intervention1

Table 2

Comparison of exercise performance indices, pre-and post-supplementation1

DISCUSSION

The main purpose of current study was to realize the effect of quercetin supplementation on exercise performance indexes including VO2max, TTE, lactate, and body fat in young female swimmers. The results of this study do not support the theory that quercetin could increase exercise performance in trained individuals. Quercetin, as a natural polyphenolic flavonol, frequently is found in the diet. Dietary records showed that Quercetin was consumed between 5 and 500 mg based on frequency of vegetable and fruit consumption. Several experimental studies indicated the health beneficial effects of flavonoids. Quercetin, because of its biological properties, has been known for its performance benefits, ergogenic and health effects in animal models. It has also been indicated that quercetin supplementation could affect aerobic capacity, exercise performance and skeletal muscle practically the same as exercise training.[14] The combination of anti-inflammatory and antioxidant activity was approved for these beneficial effects however recent studies recommended that mitochondrial biogenesis may be also responsible.[13]

Our finding from the present study failed to find any significant effect of 1000 mg quercetin supplementation for 8 weeks on exercise performance indices including VO2max, TTE, lactate, and body fat in young female swimmers. Albeit, little is known regarding the effect of quercetin in humans, finding no significant effect of quercetin supplementation in our study is in line with the most of previous studies. Previous studies on trained individuals couldn't find any improvement on physical performance.[172122] MacRae in a study couldn't find any improvement in cyclist performance after 600 mg/day quercetin supplementation for 6 weeks.[17] In another study, 1 g/day supplementation for 3 weeks in marathon runners had not any effect on race time.[22] Likewise, acute supplementation (2 g/day) on cyclists couldn't improve athlete's performance.[23] Moreover, having no change in muscle oxidative capacity and VO2max had been reported in preceding studies.[8162024] Furthermore, in another study on moderately trained military persons, quercetin supplementation (1 g/day) for 6 weeks didn't advanced exercise performance or VO2max.[25] However, other studies using 1 g/day quercetin supplementation for 1-2 weeks found a small significant improvement in physical performance in untrained or moderately trained individuals.[1619] Similarly, quercetin supplementation (1 g/day) for 5-9 days slightly enhanced VO2 max.[19] Several mechanisms may explain the possible effects of quercetin on improving VO2max and exercise performance. Based on a possible mechanism exercise performance would be supposedly improved by quercetin through reducing damage to skeletal muscle and contractile proteins, so quercetin could reduce muscle damage, tenderness, fatiguing, and negative effects of increased reactive oxygen production following exercise;[17] however, the evidences are contradictive.[2627] Another theory explained that quercetin practically the same as caffeine, by reducing the sensitivity of pain, may influence exercise performance.[28] Additionally, positive effects of quercetin on skeletal muscles may partially elucidated via increases in mitochondrial protein, stimulating mitochondrial biogenesis and increasing oxidative enzyme activity.[29-31] Failure to find a significant improvement in exercise performance indices in trained individuals in the current study could be reasoned that supplement of quercetin may improve endurance performance in untrained people.[21] In trained subjects, mitochondrial biogenesis in skeletal muscles and endurance performance has already improved as a result of exercise and no further improvement would happen due to supplementation. In addition, these results attributed to insufficient dosage for quercetin supplementation. Conversely, higher dosage of antioxidants may lead to negative antioxidant effect which could interfere with gene activation that inaugurate mithochondrial biogenesis.[6] Dietary quercetin may also be responsible for this result. Besides, several limitations should be considered in this study. First of all, we didn't evaluate the dietary quercetin intake in participants. It is possible that quercetin supplement could affect individuals with lower intake of dietary quercetin. Moreover, we couldn't evaluate the blood quercetin level. Additionally a limited number participated in this study, so the power of this study may be insufficient to find significant differences. Increasing the power of the study may find tiny differences between groups.

To sum up, quercetin supplementation at the level of 1000 g/day for 8 weeks in swimmer females didn't have any significant association with exercise performance indices. However, further studies with larger sample size and different dosage is suggested.

CONCLUSION

Additionally, positive effects of quercetin on skeletal muscles may partially elucidated via increases in mitochondrial protein, stimulating mitochondrial biogenesis and increasing oxidative enzyme activity. Failure to find a significant improvement in exercise performance indices in trained individuals in the current study could be reasoned that supplement of quercetin may improve endurance performance in untrained people.