This study examined the association between the change in step count of older adults and the BE around their homes in Yokohama, Japan, over a three-year period. The main finding was that of the 5Ds, four of the Ds (Density, Diversity, Destination accessibility, and Distance to transit) mitigated the decline in older adults’ step count corresponding with previous cross-sectional studies relating to walking and/or the PA of older adults. In addition, the association of the BE with baseline step count was examined. Comparisons of the results of the two models showed that the significant variables selected were mostly the same, and the direction of the coefficients was consistent in both models. In other words, the BEs of older adults were not only associated with their step count at a certain time point but also widened the disparity of their step count over the three years.
Regarding each variable, a lower population density was associated with a lower baseline step count, and older adults living in the lowest quartile neighborhoods of population density had significantly decreased step count during the three years. This result is consistent with a previous study that found higher baseline levels of population density were associated with greater increases in walking for transportation, although the sample was not limited to older adults [37]. Population density ensures public transport and local shops and services are more viable [38] and serves as a proxy variable showing the convenience of walking for local residents. Older adults in sparsely-populated and inconvenient areas might decrease their trip frequency or change their transportation mode from walking. It was estimated that the population of Yokohama reached its peak in 2019 and would begin declining as cities in Japan [39]. On a micro-scale level, areas that are inconvenient to reach in the city would experience a greater decrease in population, resulting in the withdrawal of facilities and even greater inconvenience to residents. Considering low residential mobility in Japan, especially that of older adults [40], health promotion interventions for PA would be necessary for such areas.
Inversely, lower intersection density was associated with higher baseline step count and a smaller decline in step count over the course of the study. High intersection density indicates there are many route opportunities for traversing a road network and is thought to promote walking [6], as previous cross-sectional studies have shown, there is a positive association between older adults’ self-reported walking and intersection density [10, 11]. In previous longitudinal studies, not limited to older adults, higher street connectivity proved to be associated with a greater increase in walking for transportation [37, 41]. Although our results contradicted these studies, another study conducted in Japan also stated that the number of intersections was negatively associated with walking time [42]. It may be that intersection density cannot be an index of walkability in a city with high intersection density like Yokohama. The intersection density in Yokohama is approximately twice the figure compared to 100 cities all over the world, excluding Japanese cities, and as high as the highest city (Lisbon, Portugal) in developed countries [43]. Considering a previous study that showed that the number of street intersections contributed to walking activity only when residents perceived that the traffic conditions were safe [11]; the older adults in neighborhoods with a high intersection density in this study might feel unsafe as intersection density acted as an index of traffic accident risk.
Regarding the average distance to the nearest railway station, older adults living in the second closest quartile neighborhood recorded a significantly higher baseline step count, which suggests that they could not walk much when living too close to stations. A walkable design where older adults feel safe and are more willing to walk around is desirable around railway stations. More importantly, it was found that older adults living closer to railway stations experienced a smaller decline in step count. Taking this into consideration with a previous study of older Japanese showing a lower risk of functional limitations among those using public transport after driving cessation [44], closeness to railway stations would enable older adults to maintain their active living, their step count, and their health even after they give up driving. Yokohama city aims to accumulate residential functions around railway stations, even in suburban areas, as well as commercial and business functions [45]. Such a compact city policy, which is thought to positively influence the overall health of city populations [46], would be more beneficial in an aging society like Yokohama city provided that consideration is given to outskirt areas, as noted above.
The other BE variables, the proportion of commercial land use, the NDVI, and the average distance to the nearest bus stop, were not significantly associated with step counts in either regression analyses. It might be because of their strong correlation with the other BE variables. Regarding personal attributes, females and the older group recorded a lower baseline step count and a larger decline over the course of the study. Additionally, a higher baseline step count was associated with a larger decline, which was consistent with a previous study [20].
While making an important contribution to existing research on BE factors that mitigate the decline in the step count of older adults, this study has limitations. For instance, previous studies showed social environmental factors, such as neighborhood cohesion [47], income deprivation [48], participation with friends [49], social support [34], and neighbor relationships [50], were associated with walking and/or PA. Unfortunately, this study was not able to assess the impact of social environments of older adults as it is difficult to collect data on social environmental factors from a large sample. Therefore, future studies should consider them when examining the longitudinal association between changes in older adults’ PA. In addition, study participants may not be representative of the general population of Yokohama city in that they were motivated to have pedometers, suggesting a greater intention to walk than others. We thought that study participants would be less affected by the BE because of their higher motivation and that the effect of the BE would be underestimated in this study.