The Potential of Physical Exercise to Mitigate Radiation Damage-A Systematic Review

Abstract

There is a need to investigate new countermeasures against the detrimental effects of ionizing radiation as deep space exploration missions are on the horizon. Objective: In this systematic review, the effects of physical exercise upon ionizing radiation-induced damage were evaluated. Methods: Systematic searches were performed in Medline, Embase, Cochrane library, and the databases from space agencies. Of 2,798 publications that were screened, 22 studies contained relevant data that were further extracted and analyzed. Risk of bias of included studies was assessed. Due to the high level of heterogeneity, meta-analysis was not performed. Five outcome groups were assessed by calculating Hedges' g effect sizes and visualized using effect size plots. Results: Exercise decreased radiation-induced DNA damage, oxidative stress, and inflammation, while increasing antioxidant activity. Although the results were highly heterogeneous, there was evidence for a beneficial effect of exercise in cellular, clinical, and functional outcomes. Conclusions: Out of 72 outcomes, 68 showed a beneficial effect of physical training when exposed to ionizing radiation. As the first study to investigate a potential protective mechanism of physical exercise against radiation effects in a systematic review, the current findings may help inform medical capabilities of human spaceflight and may also be relevant for terrestrial clinical care such as radiation oncology.

Keywords: DNA damage; deep space exploration; human spaceflight; ionizing radiation; oxidative stress; physical exercise; radiation countermeasures.

Figure 1

Flow diagram of search and screening methodology. The flow of search results, numbers, and author's eligibility screening assessment is represented here.

Figure 2

Effect of exercise intervention explained by experimental conditions. (A) Sankey diagram showing the effect sizes for all human and animal studies. The string thicknesses refer to the total number of outcomes for each category. “Mod.” —Moderate, “Neg.”—Negative, “Null “—No effect. (B) Effect size scatter plot showing all human and animal outcomes. Pre, During, and Post refer to the time at which the exercise intervention was applied with respect to the radiation exposure. The size of bubbles represents the effect sizes for each outcome represented.

Figure 3

Effect size plot of antioxidant activity, DNA damage, and inflammation. Outcomes are plotted with the Hedges' g calculated for each outcome extracted and bias corrected for sample size. Confidence intervals of 95% are represented by the error bars. Effect size values that are in the positive rightward direction indicate a beneficial effect in favor of the exercise intervention group compared to the non-exercise control group. Shapes refer to the time at which the exercise intervention was applied with respect to the radiation exposure (Post—Circle, Pre—Square, During—Triangle).

Figure 4

Effect size plot of neurogenesis in animal studies. Outcomes are plotted with the Hedges' g calculated for each outcome extracted and bias corrected for sample size. Confidence intervals of 95% are represented by the error bars. Effect size values that are in the positive rightward direction indicate a beneficial effect in favor of the exercise intervention group compared to the non-exercise control group. Shapes refer to the time at which the exercise intervention was applied with respect to the radiation exposure (Post—Circle).

Figure 5

Effect size plot of behavior in animals and fatigue in human trials. Outcomes are plotted with the Hedges' g calculated for each outcome extracted and bias corrected for sample size. Confidence intervals of 95% are represented by the error bars. Effect size values that are in the positive rightward direction indicate a beneficial effect in favor of the exercise intervention group compared to the non-exercise control group. Shapes refer to the time at which the exercise intervention was applied with respect to the radiation exposure (Post—Circle, Pre—Square, During—Triangle).

Figure 6

Effect size plot of cellular and tissue function in animal studies. Outcomes are plotted with the Hedges' g calculated for each outcome extracted and bias corrected for sample size. Confidence intervals of 95% are represented by the error bars. Effect size values that are in the positive rightward direction indicate a beneficial effect in favor of the exercise intervention group compared to the non-exercise control group. Shapes refer to the time at which the exercise intervention was applied with respect to the radiation exposure (Post—Circle, Pre—Square).