Effects of a walk in a residential natural vs. urban environment on objective and subjective stress indicators in mothers and their infants

Despite growing evidence that being in nature positively influences mood and stress, its effects on children are not well understood. Previous cross-sectional research suggests that greater green space in children's residential environments is associated with better mental health outcomes, but the causal relationship remains unclear. Moreover, the impact of such environments on infants has not yet been explored. To address these gaps, we conducted an experimental intervention study with 72 mother-infant dyads (mean infant age = 7.5 months) to examine the effects of natural vs. urban environments on their stress. To enhance ecological validity, the study took place in residential, everyday environments, and the walks were conducted independently of the experimenter team. The study employed a randomised crossover trial, in which each mother-infant pair completed two 45-min walks, one in a natural setting and one in an urban area. We assessed subjective and physiological stress indicators, including maternal self-reported stress, salivary cortisol in mothers and infants, and cortisol levels in mothers' breast milk. The results showed that mothers' subjective stress levels decreased after both walks (p = 0.001), accompanied by a reduction in arousal (p < 0.001). Additionally, salivary cortisol concentrations decreased after walks in both environments for mothers (p = 0.007) and infants (p = 0.007). Mothers further reported increased calmness (p = 0.001), greater pleasantness (p = 0.002), and improved mood (p < 0.001) after the both walks, while also rating the nature walk as more enjoyable (p < 0.001) and more attention-restorative (p < 0.001) than the urban walk. However, the type of environment did not significantly affect subjective or physiological stress levels in mothers and infants. These findings suggest that taking a walk outdoors was associated with reduced stress in mothers and infants, but that the environment may play less of a role in this effect. The results underscore the complex relationship between environmental exposure and stress, offering insights for future research into how different environments influence early-life stress regulation.