The mediating effect of environmental reward on activity restriction and depressive mood in cancer survivors: a cross-sectional study

Abstract Background: Activity restriction is known as a predictor of depressive mood in cancer survivors. However, there is inconsistent evidence about precisely how this takes place. Environmental reward is a state where a person senses mastery or pleasure because of their activity, and this is known to be a possible mediator of the activity restriction effect on depressive mood. We sought to investigate that the mediating effect environmental reward could have on the relationship between activity restriction and depressive mood when moderated by cancer-related fatigue. Methods: Cancer survivors (n = 94; mean age, 60.07 years) recruited through cancer support groups in Japan participated in this study. They completed a battery of questionnaires, including demographic and clinical information about the respondents, the Activity Restriction Scale for Cancer Patients—Revised, the Environmental Reward Observation Scale, the Cancer Fatigue Scale, and the Hospital Anxiety and Depression Scale. Results: Moderated mediation analysis revealed that high levels of activity restriction predict a decrease in environmental reward, and a decrease in environmental reward exacerbates depressive mood. The full mediating effect (when the indirect effect is statistically significant and there is no direct effect from the antecedent to outcome) of environmental reward was observed when cancer-related fatigue was moderated by ±1 SD of the mean score. This implies that, regardless of the level of fatigue cancer survivors experience, it is not the activity restriction per se that predicts depressive mood but rather the inability to experience pleasurable emotions because of the activity restriction that leads to the exacerbation of depressive mood. Conclusion: From these results, environmental reward was found to be a possible mediator of activity restriction on depressive mood, consistent with behavioral models of depression. These results could explain the inconsistent findings about the direct effect of activity restriction on depressive mood and provide theoretical evidence for the effectiveness of psychological treatments for cancer survivors that focus on positive affect, such as behavioral activation interventions.