Research Article: Effects of antioxidant-rich foods on altitude-induced oxidative stress and inflammation in elite endurance athletes: A randomized controlled trial

Date Published: June 13, 2019

Publisher: Public Library of Science

Author(s): Anu Elisa Koivisto, Thomas Olsen, Ingvild Paur, Gøran Paulsen, Nasser Ezzatkhah Bastani, Ina Garthe, Truls Raastad, Jason Matthews, Rune Blomhoff, Siv Kjølsrud Bøhn, Cristina Vassalle.

http://doi.org/10.1371/journal.pone.0217895

Abstract

Various altitude training regimes, systematically used to improve oxygen carrying capacity and sports performance, have been associated with increased oxidative stress and inflammation. We investigated whether increased intake of common antioxidant-rich foods attenuates these processes.

In a randomized controlled trial, 31 elite endurance athletes (23 ± 5 years), ingested antioxidant-rich foods (n = 16), (> doubling their usual intake), or eucaloric control foods (n = 15) during a 3-week altitude training camp (2320 m). Fasting blood and urine samples were collected 7 days pre-altitude, after 5 and 18 days at altitude, and 7 days post-altitude. Change over time was compared between the groups using mixed models for antioxidant capacity [uric acid-free (ferric reducing ability of plasma (FRAP)], oxidative stress (8-epi-PGF2α) and inflammatory biomarkers (IFNγ, IL1α, IL1RA, IL1β, IL2, IL5, IL6, IL7, IL10, IL12p70, IL13, IL17, TNFα, MCP-1 and micro-CRP). The cytokine response to a stress-test (VO2max ramp test or 100 m swimming) was assessed at pre- and post-altitude.

FRAP increased more in the antioxidant compared to the control group (p = 0.034). IL13 decreased in the antioxidant group, while increasing in the controls (p = 0.006). A similar trend was seen for IL6 (p = 0.062). A larger decrease in micro-CRP was detected in the antioxidant group compared to controls (β: -0.62, p = 0.02). We found no group differences for the remaining cytokines. 8-epi-PGF2α increased significantly in the whole population (p = 0.033), regardless group allocation. The stress response was significantly larger post-altitude compared with pre-altitude for IL1β, IL6, IL7, IL13, IL12p70 and TNFα, but we found no group differences.

Increased intake of antioxidant-rich foods elevated the antioxidant capacity and attenuated some of the altitude-induced systemic inflammatory biomarkers in elite athletes. The antioxidant intervention had no impact on the altitude-induced oxidative stress or changes in acute cytokine responses to exercise stress-tests.

Partial Text

Several endurance athletes incorporate various hypoxic training modalities to their annual training plan to increase their oxygen carrying capacity and ultimately improve sports performance [1]. The combination of hypoxia and exercise can result in a more pronounced impact on immune system than hypoxia or exercise alone [2–4]. During altitude training camps athletes seem to be at increased risk for immunological disturbances, infections and illness [4–6], which may jeopardize the desired altitude-induced increase in hemoglobin mass [7, 8]. The systemic concentration of several inflammatory cytokines increases following training at altitude illustrating an immune system response to hypoxia [9, 10]. Altitude training is also associated with an elevation in free radical production, reduction in plasma antioxidant capacity and subsequent increase in oxidative stress [11–13]. Both acute [14] and long-term hypoxic exposures [15, 16] augment oxidative stress, and the magnitude of the oxidative stress response seems to depend on the total hypoxic dose (duration and meters above sea level) [17]. Although the underlying mechanisms of hypoxia-induced reactive oxygen species (ROS) overproduction are not entirely clear, reductive stress within the mitochondria, augmented catecholamine production, decreased mitochondria redox potential and xanthine oxidase pathway activation, have previously been suggested [12].

This study is the first to examine whether increased intake of antioxidant-rich foods during a 3-week training camp at moderate altitude affects systemic oxidative stress and inflammation at rest and in response to maximal physical exertion in elite endurance athletes.

The present study is the first to examine the impact of increased intake of antioxidant-rich foods on the oxidative and inflammatory response to altitude training (2320 m) in elite endurance athletes. We observed that more than doubling the daily antioxidant intake from natural food sources (e.g. fruit-berry-vegetable smoothies, nuts, dark chocolate and dried fruits/berries) in elite athletes increased the antioxidant capacity but did not affect oxidative stress as measured by 8-epi-PGF2α. Also, increased antioxidant-rich food intake attenuated the altitude-induced increases in systematic inflammatory biomarkers (micro-CRP, IL13, IL6), although it did not affect the altitude-induced inflammatory response to exercise stress-test. In addition, since the groups had similar beneficial increases in hemoglobin mass in response to the altitude training as previously reported [30], we suggest that increasing intake of natural antioxidant-rich foods is a sensible addition to elite athlete’s dietary routines while training at moderate altitude.

 

Source:

http://doi.org/10.1371/journal.pone.0217895

 

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