To our knowledge this is the first study to investigate the cumulative influence of favorable environmental factors on older adults’ walking for transportation by categories of perceived distance to destinations. Our hypothesis that there is a cumulative effect of favorable environmental factors on older adults’ walking for transportation was partially confirmed by our findings. A cumulative relationship was observed when participants lived within short, but especially within medium distance to destinations. However, in line with our second hypothesis, a cumulative relationship was absent when participants lived within large distance to destinations.
Independent of the presence of other favorable environmental factors, participants living within short distance to destinations were more likely to walk daily for transportation. This is consistent with several recent studies reporting a positive relationship between older adults’ walking for transportation and the perceived and objective presence of nearby facilities[14–16]. Hence, recent changes in local communities’ structures, particularly in terms of the closure of facilities and services (e.g. post offices, bakeries), might negatively affect older adults’ walking for transportation. An increase in probabilities of daily walking for transportation was only observed when at least seven favorable environmental factors were present. It seems that a short distance to destinations is an important facilitator of walking for transportation and that an accumulation of multiple favorable environmental factors (seven in the current study) are needed to further stimulate walking for transportation.
A clear cumulative effect of favorable environmental factors was observed among participants who perceived facilities to be located within medium distances from their homes. Our findings showed that at least four favorable environmental factors needed to be present to find a significant influence on older adults’ walking for transportation. The presence of additional favorable environmental factors did not further increase probabilities of daily walking for transportation. This is similar to the results reported by Sallis and colleagues who found that at least four favorable environmental factors needed to be present to find a significant relationship with total PA levels in adults. Two very recent studies also reported similar (curvilinear) dose-response relationships between environmental indices and adults’ total sitting time, motorized transport and walking and cycling for transportation. Our findings suggest that a favorable walking environment can motivate older adults to walk moderate distances to facilities. However, they also suggest that the modification of single environmental characteristics are unlikely to result in increasing levels of older adults' walking for transportation unless other favorable environmental factors are already in place. This implies that environmental programs to promote walking for transportation should apply different strategies depending on the target area. How many and which environmental factors should be modified will depend on the environmental features that are already present. Based upon our findings it is not possible to state if certain combinations of environmental factors are more or less effective to promote walking for transportation compared to other combinations. Future research is needed to investigate this issue.
No relationship between the presence of favorable environmental factors and daily walking for transportation was observed if participants perceived distance to destinations to be large. Apparently, a large distance to destinations forms such a strong deterrent to daily walking for transportation that it cannot be overcome by the presence of multiple favorable environmental factors. Similarly, other deterrents (e.g. low perceived safety from crime) that cannot be overcome by the presence of one or more favorable environmental might exist. Such interaction effects should be investigated in future research. Promoting walking for transportation by means of environmental modifications in areas with restricted access to destinations might involve supporting maintenance of local shops and services and attracting new shops and services (e.g. through tax incentives). Furthermore, the possibility of changing older adults’ perception of a “walkable” distance and its effects on walking for transportation should be explored.
Several strengths and weaknesses of this study should be considered. A first strength is the investigation of the cumulative influence of multiple favorable environmental factors on older adults’ walking for transportation rather than the influence of each environmental factor separately. Studying the moderating effect of distance to destinations on this relationship is another innovation in this research area. Secondly, these analyses were carried out on a large sample of older adults. However, despite the large sample size, caution is needed while interpreting the results. Few participants reported a low and high number of favorable environmental factors which resulted in a widening of the confidence intervals for these values. Future research including very unfavorable and favorable walking environments is needed to confirm current findings. Furthermore, residential densities in the participating municipalities were higher than in the average Flemish municipality. Since Flanders is already a very densely populated region, research in other (less dense) countries is needed to confirm current findings. This emphasizes the need for (international) studies which cover a wide variety of environmental contexts. A second limitation is the absence of information on the psychometrics of the measure of walking for transportation. Furthermore, this measure captured frequency but not duration or intensity of walking for transportation. Thirdly, this study relied on subjective rather than objective environmental measures on a limited set of environmental factors. For example, this study did not include a measure of aesthetic features of the environment. Finally, inferring causal conclusions is not possible because of the cross-sectional study design.
In conclusion, there appears to be a cumulative influence of physical environmental factors on older adults’ walking for transportation. However, this relationship was moderated by distance to destinations. These cumulative effects of and interaction effects between environmental factors offer a possible explanation for the inconsistencies between previous studies. Our findings highlight the need for future research to study the relationship between older adults’ PA and multiple environmental factors simultaneously instead of separately. Further research should reveal which combinations of environmental factors need to be present to optimally stimulate older adults’ walking for transportation in areas with different access to facilities. If the current findings are confirmed, interventions should not only target multiple levels, such as the person within his social, physical and policy environment, but also multiple factors within the physical environment.