Control of antioxidant supplementation through interview is not appropriate in oxidative-stress sport studies: Analytical confirmation should be required

Highlights

• Antioxidant supplementation should be controlled in oxidative-stress sport studies.

• Personal interviews are weak tools to verify antioxidant supplementation.

• Twenty percent of the participants lied in the personal interview; these participants showed high plasma α-tocopherol levels.

• High concentration of antioxidants affected oxidative stress, altering final results.

• High-performance liquid chromatography technique is suggested to detect hidden antioxidant supplementation.

Abstract

Objective

Controlling antioxidant supplementation in athletes involved in studies related to oxidative stress and muscle damage is the key to ensure results. The aim of this study was to confirm through high-performance liquid chromatography (HPLC) analysis whether well-trained individuals lied during a personal interview when asked if they were taking supplements with antioxidants, and how this could affect oxidative stress, muscle damage, and antioxidant response.

Methods

A total of 94 men, well trained in endurance sports, volunteered in this study. They denied taking any antioxidant supplementation at initial interview. After a HPLC analysis, abnormal α-tocopherol concentrations were detected, probably due to a hidden antioxidant supplementation. Participants were classified into two groups: no evidence of antioxidant supplementation (NS group = α-tocopherol values <80 nmol/mL; n = 75) and evidence of antioxidant supplementation (S group = α-tocopherol values >80 nmol/mL; n = 19). Lipid peroxidation, muscle damage, antioxidant enzyme activity, and nonenzymatic antioxidant content were analyzed according to this classification. Statistical comparisons were performed using Student's t test.

Results

The α-tocopherol concentrations were significantly higher in the S group than in the NS group (MD = 725.01 ± 39.01 nmol/mL; P = 0.001). The S group showed a trend toward lower hydroperoxides than the NS group (MD = 1.19 ± 0.72 nmol/mL; P = 0.071). The S group showed significantly lower catalase activity than the NS group (MD = 0.10 ± 0.02-seg-1 mg-1; P < 0.01). Skeletal muscle damage markers did not differ between experimental groups.

Conclusions

Data from the present study reveal that 20% of participants lied in the exclusion criteria of antioxidant supplementation in a personal interview, as they showed high plasmatic α-tocopherol concentrations after HPLC verification. Catalase activity seems to be affected by high α-tocopherol plasma levels. Therefore, we strongly recommend the HPLC analysis as a necessary tool to verify the antioxidant intake and preserve results in studies linking oxidative stress and sport.

Introduction

In studies measuring the oxidative stress induced by exercise and/or nutrition, researchers must take into account the intake of antioxidant supplements as exclusion criterion as this supplementation can alter results [1]. Despite several validated qualitative instruments to evaluate the supplementation [2], [3], data collected using a self-report questionnaire might not be sufficient for obtaining reliable information. Although the personal interview seems to be reliable [4], it is susceptible to error [5]. Specifically, in sport studies, the majority of athletes and well-trained individuals do not feel comfortable discussing this topic with researchers. Thus, they might lie or they might not clearly express their opinions despite confidentiality guarantees [6]. Thus, studies in which is necessary to control the antioxidant intake may be subject to error if only indirect instruments such as interviews or questionnaires are used.

Moreover, the intake of antioxidant supplements should be controlled because there is a lack of scientific evidence regarding their long-term effects [7]. Although it is established that chronic endurance training generates beneficial effects by improving antioxidant defense and reducing lipid peroxidation [8], [9], well-trained individuals commonly continue using vitamins and antioxidant supplements to aid recovery and performance and to improve health [10]. However, most of the studies about antioxidant supplementation in endurance exercise have concluded that there are controversial changes in oxidative response after acute exercise [11], [12]. The physiological consequences of vitamin E supplementation in athletes regarding their health, prolonging their life, and improving sports performance is debatable [13], [14]. Whereas some studies suggest beneficial effects [15], others showed damage in the cell function [16], no beneficial effects on muscle damage and oxidative stress [17], negative side effects [18], or still unknown long-term effects [19], probably due to the lack of standardized protocols and variety of doses [20].

For that reason, it is important to test the hypothesis that some athletes who respond to an interview in studies about oxidative stress and exercise might answer untruthfully to avoid being excluded because of antioxidant supplement intake. Additionally, this hidden antioxidant supplementation could affect antioxidant capacity, oxidative stress response, and skeletal muscle damage. Thus, a direct and quantifiable method should be used as there might be a significant difference among what athletes say, think, and do, and the results may be contaminated. Hence, the purpose of this study was to confirm through direct measure (high-performance liquid chromatography [HPLC]) whether individuals who are well trained in endurance sports lie during a personal interview when asked the following in the exclusion criterion: “Are you taking supplements with antioxidants?” and how antioxidant supplementation might interfere with oxidative stress, muscle damage, and antioxidant capacity.