Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sport Nutr. Exerc. Metab.
Page numbers: 291-298
doi (if applicable):
Summary of Background and Research Design
Background:Reactive oxygen species (ROS) are generated during exercise. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) are plasma antioxidant enzymes that protect the body from harmful effects of ROS. It has been shown in adults that exercise induces production of these enzymes so people who exercise more have higher serum concentrations of GPx and SOD. However, people involved in regular exercise may also have differences in dietary patterns, especially in relation to intakes of trace elements such as selenium (Se), copper (Cu), and zinc (Zn) that are cofactors of GPx and SOD.
Hypothesis:Adolescent female gymnasts have higher plasma levels of GPx and SOD than their sedentary counterparts.
Secondary research question: What is the association between habitual exercise, trace-element status, age, body size, and dietary intakes of trace elements?
Subjects: British females aged 8-17 were recruited. 38 gymnasts who trained >= 10 hrs/wk and competed in at the regional level composed one group and 40 non-gymnasts served as controls. The controls were involved in normal physical activity but not in sports that require year-round training.
Experimental design:Blood samples were collected in the late afternoon to assess serum antioxidant enzyme concentration and trace elements. Dietary records were obtained for one week, but not during a holiday or right before competition for the gymnasts.
Treatments and protocol:No intervention.
Summary of Research Findings
- There was no difference in energy or dietary antioxidant intake between the two groups.
- Serum GPx concentrations were significantly higher in gymnasts vs. non-gymnasts (157 ± 11 U/mL in gymnasts vs. 125 ± 9 U/mL in controls, P = 0.033).
- Serum SOD concentration was lower for gymnasts (7.23 ± 0.41 U/mL for gymnasts vs. 8.57 ± 0.38 U/mL for controls, P = 0.010).
- Serum Se concentrations were also higher in gymnasts despite their lower dietary intake of selenium.
- There was no significant difference between groups for serum Cu or Zn.
- A positive association was observed between levels of physical activity and serum Zn concentrations in both groups.
- No significant correlations were observed between dietary micronutrients (Zn; Se; vitamins A, C, and E) and antioxidant enzymes or trace-element concentrations in either group.
Interpretation of findings/Key practice applications:
Although exercise generates high amounts of ROS, habitual physical activity is likely responsible for compensatory induction of antioxidant defenses such as GPx, but not SOD. Increased dietary intake of Zn, Se, or Cu is required for this induction.
Only one blood sample was taken from each girl in a non-fasted state. Therefore, blood levels of antioxidant enzymes and trace metals from this one blood sample may not be representative of fasting levels or circulating levels as a whole. These levels can fluctuate with meals prior to the blood draw and menstrual status.