Sidewalks may curb dementia risk in urban areas

Living in neighbourhoods with liberal sidewalk coverage contributes to a lower incidence of dementia in urban areas, a study from Japan has found.

The benefit, however, is absent in rural areas, according to the investigators. “This … is plausible, as people living in rural areas can walk about and talk safely without sidewalks without the worry of traffic that plagues urban areas.

“[Also], in rural areas, the percentage of people using cars is higher and the frequency of going out is lower than in urban areas. These factors suggest that rural people may be less exposed to sidewalks, and sidewalks may therefore not be associated with dementia incidence,” they explained.

Studies have been driving home the message that people are better off spending more time exercising to ward off age-related cognitive decline and prevent dementia. For older people, walking is the most accessible type of physical activity, as it is low cost, presents low risk for ageing bodies, and is applicable to various activities such as shopping and sightseeing. [Int J Behav Nutr Phys Act 2017;14:103; Am J Health Promot 2004;18:435-443; Int J Behav Nutr Phys Act 2014;11:79]

“Sidewalks may prompt people to walk, and walkability of paths positively motivates older people to engage in physical activity,” according to the investigators.

In the study, the investigators looked at 76,053 participants (53.4 percent female; 69 percent married; 21 percent employed) of Japan Gerontological Evaluation Study, a population-based cohort study of community-dwelling older adults. About 30 percent of them walked >1 hour a day, >50 percent went out more than four times per week, and 66 percent used a car when going out. 

The mean sidewalk coverage within the 436 elementary school districts (average area, 2.65 km²) was 13.8 percent, yielding an estimated sidewalk installation percentage of 37.9 percent. The difference between the highest (Q4) and lowest (Q1) quartile of coverage was more than threefold (58 percent vs 18 percent). [Am J Epidemiol 2021;doi:10.1093/aje/kwab043]

Coverage was positively correlated with sidewalk area, population density, and number of hospitals, grocery stores, parks, and railway stations, proportion of higher education, and unemployment rate. Conversely, it showed an inverse association with road area, area of school district, and land slope.

Over a follow-up of 3 years, 5,310 participants developed dementia. In urban areas, higher sidewalk coverage served as a defense against dementia (Q4 vs Q1: hazard ratio [HR], 0.42, 95 percent confidence interval [CI], 0.33–0.54). This association persisted even after successive adjustments for other neighbourhood factors (HR, 0.75, 95 percent CI, 0.59–0.94).

“Little attenuation of the association between sidewalk coverage and dementia was found after adjustments for physical activity. One reason may be mismeasurement of physical activities. As we examined only the self-reported walking times, the frequency of outings and car use, it may not reflect the actual physical activities of older people,” the investigators acknowledged.

They pointed out that even if participants went out frequently, they might have taken the car for transport rather than gone by foot. Not surprisingly, higher sidewalk coverage was protective against dementia only among noncar users.

“Because older people may be unable to use a car for several reasons such as loss of driving license or loss of family member responsible for driving, this result may be important for public health. We found that walking time did not vary with sidewalk coverage,” the investigators said.

“One possibility is that we should account for landscapes such as roadside vegetation to encourage walking, because older people place importance on ‘changing landscapes’ such as growth of plants when selecting places to walk,” they added. [Occup Environ Med 2010;67:111-117]

The current study adds weight to the notion that place of residence can affect dementia risk and describes the potential impact of these findings on dementia research by proposing a new modifiable environmental risk factor, according to the investigators. “Indeed, urban planning could be a new way to promote healthy ageing, if the present results are confirmed.”