An immodest proposal: Implementing walkable communities for the good of eye care

The US spends more than $400 billion on diabetes care and lost productivity every year, so prevention is key. Image credit: AdobeStock/Dmytro

It is well established that multiple environmental factors contribute to the development of diabetes. Although obesity appears to be the single most important risk factor for (type 2) diabetes risk, myriad other exposures beyond individual control have been causally linked to insulin resistance, overweight and obesity, and the pathological genesis of type 2 diabetes mellitus (T2DM). For example, particulate air pollution is estimated to cause 20% of worldwide diabetes cases,¹ based on epidemiologic and cellular evidence that increasing exposure to particles < 2.5 micrometers in size (PM25) concomitantly worsens inflammation (via inflammatory cytokines such as interleukin-6, tumor-necrosis factor-α, and C-reactive protein), mitochondrial reactive oxygen species resulting in β-cell dysfunction combined with reduced insulin sensitivity, and endoplasmic reticulum stress resulting from protein misfolding that reduces pancreatic β-cell survival.²

Similarly, gene-wide associated studies show that T2DM is a polygenic disease with 30% to 70% heritability depending on specific phenotype, including findings that maternal T2DM changes mitochondrial DNA in ways that significantly increase the risk of obesity and T2DM in offspring.³ Ambient air temperatures, microplastic contamination of food and water supplies, and material inequality/food insecurity have also been causally linked to diabetes risk.

One of the environmental diabetogenic factors I’d like to draw attention to is the ease with which our patients can walk within their communities—to work, to school, to businesses, to social gatherings, and for pleasure. The National Diabetes Prevention Program (DPP), as we all should know, showed that walking 150 minutes per week significantly lowered the risk of developing T2DM in high-risk patients compared with metformin or usual care, a finding that was maintainable beyond 2 decades of follow-up.⁴ What the DPP didn’t consider, however, was the environment in which our patients can walk efficiently and safely within their communities.

Recently, an interesting analysis of identical and same-sex fraternal twins looked at exactly this question and found that neighborhood “walkability” independently predicted the amount and duration of walking. Specifically, the authors analyzed 5477 monozygotic and same-sex dizygotic pairs as “quasi-experimental” controls for genetic and shared environment influences. Walkability was calculated using key neighborhood features, including intersection density, population density, and destination accessibility. Self-reported weekly minutes of neighborhood walking and moderate to vigorous physical activity and days per week using transit services (eg, bus, commuter rail) showed a positive association between walkability and walking, with a 1% increase in walkability being associated with a 0.42% increase in neighborhood walking. Higher walkability reduced the probability of no transit use by 32%, considering familial and demographic factors.⁵ A walkability score for every US zip code on a scale of 0 to 100 (least to most walkable) is available at https://www.walkscore.com/.

Similarly, analysis of 2020 National Health and Nutrition Examination Survey data of more than 31,000 US adults found that “high-walkability” neighborhoods were associated with 48% more physical activity and 24% less obesity compared with low-walkability neighborhoods.⁶ These 6 results aren’t controlled for familial factors, as is the aforementioned study, but are nonetheless interesting. These numbers raise the question of how to make our neighborhoods more walkable. The answers will surprise no one: commitment to better public health and money.

Figure. Smart crosswalks in Oslo, Norway, separate pedestrians, bicyclists, and automobiles at intersections with sidewalks. Image courtesy of https://www.ontheroadtrends.com/protected-intersections-solution-to-improve-road-safety/?lang=en

Multiple barriers to walkability include things like lack of sidewalks, poor street connectivity, high traffic volume, wide roads, inadequate pedestrian crossings, lack of nearby destinations, poor lighting, safety concerns from crime, uneven terrain, inadequate accessibility for people with disabilities, long distances between destinations, poor weather conditions, and a lack of shade or green spaces, all of which can discourage people from walking in their neighborhood.⁷ Many of these barriers can be eliminated or improved by thinking smartly and equitably about city and neighborhood planning, including wider sidewalks, better lighting, provision of more and more inviting green spaces, and “smart crosswalks” that ensure higher levels of safety. Oslo, Norway, reduced pedestrian injury and death by 100% by introducing sidewalks that separate bicyclists, pedestrians, and automobiles at intersections⁸ (Figure).

My immodest proposal is that we significantly increase rates of walking and reduce rates of diabetes by making and remaking our communities and neighborhoods more walkable. This is a massive undertaking that requires collaboration among local/regional/state governments, city planning engineers, commercial and residential construction lenders, and the neighborhoods and people all of these groups ostensibly serve. The costs are great, but the economic and public health benefits are potentially far greater.⁹

The US spends more than $400 billion on diabetes care and lost productivity every year, so prevention is key. Taxing the production and consumption of injurious foods is 1 politically contentious option for funding, but long-term planning for improved public health will be required to realize long-term economic gains. Renowned political psychologist Professor Shawn Rosenberg claims that American democracy is doomed because Americans are too stupid, irrational, and self-obsessed to govern themselves without the protection of knowledgeable elites who check the base impulses of the general population.¹⁰ I say that Rosenberg is wrong, that, in fact, we have barely even tried to solve some of our most worrying collective challenges through democratic means—but we the people all need to bloody well prove it.

References:

1. GBD 2019 Diabetes and Air Pollution Collaborators. Estimates, trends, and drivers of the global burden of type 2 diabetes attributable to PM_2·5 air pollution, 1990-2019: an analysis of data from the Global Burden of Disease Study 2019. Lancet Planet Health. 2022;6(7):e586-e600. doi:10.1016/S2542-5196(22)00122-X

2. Li Y, Xu L, Shan Z, Teng W, Han C. Association between air pollution and type 2 diabetes: an updated review of the literature. Ther Adv Endocrinol Metab. 2019;10:2042018819897046. doi:10.1177/2042018819897046

3. Laakso M, Fernandes Silva L. Genetics of type 2 diabetes: past, present, and future. Nutrients. 2022;14(15):3201. doi:10.3390/nu14153201

4. Diabetes Prevention Program Research Group. Long-term effects of lifestyle intervention or metformin on diabetes development and microvascular complications over 15-year follow-up: the Diabetes Prevention Program Outcomes Study. Lancet Diabetes Endocrinol. 2015;3(11):866-875. doi:10.1016/S2213-8587(15)00291-0

5. Duncan GE, Hurvitz PM, Williams BD, et al. Association between neighborhood walkability and physical activity in a community-based twin sample. Am J Epidemiol. 2025:194(2):340-348. doi:10.1093/aje/kwae170

6. Wang ML, Narcisse MR, McElfish PA. Higher walkability associated with increased physical activity and reduced obesity among United States adults. Obesity (Silver Spring). 2023;31(2):553-564. doi:10.1002/oby.23634

7. Suzuki R, Blackwood J, Webster NJ, Shah S. Functional limitations and perceived neighborhood walkability among urban dwelling older adults. Front Public Health. 2021;9:675799. doi:10.3389/fpubh.2021.675799

8. Marshall WE, Ferenchak NN. Why cities with high bicycling rates are safer for all road users. Journal of Transport & Health. 2019;13:100539. https://doi.org/10.1016/j.jth.2019.03.004

9. Shin HS, Woo A. Analyzing the effects of walkable environments on nearby commercial property values based on deep learning approaches. Cities. 2024;144:104628. doi:10.2139/ssrn.4092286

10. Rosenberg S. Democracy Devouring itself: the rise of the incompetent citizen and the appeal of right wing populism. In: Rosenberg, S. Psychology of Political and Everyday Extremism. UC Irvine Previously Published Works; 2019.