Introduction

Climate change is arguably one of the biggest health threats today and is estimated to cause approximately 250,000 additional deaths per year between 2030 and 2050 [1, 2] , likely caused by thermal stress, malnutrition, infectious diseases, extreme weather events, wildfires, displacement, and so on [3–8] . The increase in global temperatures has strongly influenced the quantity and variability of natural disasters [7]. Natural disasters directly impact communities through hurricanes, floods, and raging wildfires [7, 9]. Climate change significantly increases human exposure to environmental hazards such as heatwaves and extreme heat events [10], drought, wildfires, and extreme weather events such as storms and hurricanes [11]. Furthermore, climate change increases air pollution [12] and reduces air quality [13–15]. These events lead to an increased risk of displacement [16], medical and/or food supply shortages [17, 18], hospitalizations [19, 20], chronic complications [13], and death [13, 21].

Environmental diabetology refers to the study of how geophysical phenomena impacts a person living with diabetes. Environmental diabetology explores environmental effects on diabetes metabolic control, supplies (e.g., glucometers and insulin pumps), medications, and access to care [17].

Many of the events induced by climate change can have both direct and indirect effects on an individual’s blood glucose levels, leading to poor glycemic control. Individuals may experience hypoglycemia, hyperglycemia, and diabetic ketoacidosis (DKA) events [22]. Worsened glycemic control in diabetes patients has been documented following earthquakes [17], hurricanes, [23] and after exposure to colder temperatures [24].

Diabetes affects one in ten people globally [25], and the number of people living with diabetes (PWD) has quadrupled in the last 30 years [26]. These staggering numbers highlight a growing population of individuals at increased risk from the adverse effects of climate change.

Much of the published literature on environmental diabetology is related to the increased incidence and prevalence of diabetes; [27, 28]. In this scoping review, we seek to understand the impact of climate change on PWD.

Materials and methods

This scoping review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews (PRISMA) — Scoping Reviews guidelines [29] following the Arksey and O’Malley’s methodologic framework [30] (Suppl. Tab. 1–2).

Scoping review question

How does climate change impact people living with diabetes?

Protocol and eligibility criteria

The scoping review search terms used by reviewers included type 1 diabetes OR type 2 diabetes OR diabetes AND climate change OR global warming OR natural disasters OR environmental justice in PubMed Central and Google Scholar databases (Tab. 1). The terms “environment” and “physical environment” were purposefully excluded from the search criteria because preliminary searches using those terms retrieved a broad array of papers outside the scope of the review, such as metabolic and hormone pathway processes leading to the development of diabetes rather than how the factors of climate change affect the lives of PWD. Initially, the authors agreed upon using synonyms and search terms that aligned with the global warming phenomenon, climate change, and natural disasters, to ensure a targeted review. The authors decided to perform a second search utilizing global warming as a search term, to capture any newly published studies and to make sure no major papers that used global warming as a key term were missing from the search.

Human randomized controlled trials, non-randomized controlled trials, interrupted time series, controlled before-and-after studies, cohort studies, case reports, cross-sectional, mixed methods, and case series published between 1970–2022 in the English language were eligible for inclusion. Animal studies and studies not in English, and that were outside of the established timeframe were excluded from this review. Additionally, studies that did not reference diabetes specifically, described environmental impacts broader than climate change or natural disasters, or described diabetes incidence rather than the impact on people already living with diabetes were excluded.

The first (EO), second (HH) and third (AM) authors independently reviewed the titles and abstract from an initial search conducted between November 29th through December 16th, 2022. With input from a senior author (OE), all authors resolved any disagreements via consensus discussion. A total of 10,516 articles emerged from using the aforementioned search terms, except for global warming. After applying the inclusion and exclusion criteria, the number of eligible articles was reduced to 340 following title reviews. Thereafter the first three authors screened the abstracts of eligible articles resulting in 40 studies included in the review. An additional review was conducted from February 1st to February 7th, 2023, with an emphasis on global warming and diabetes. Similar exclusion criteria were applied for the first search. Search terms included diabetes AND global warming. This search yielded 3322 articles from PubMed and Google Scholar. After examining these articles, and applying inclusion and exclusion criteria, two additional articles were included in the review (Fig. 1). Articles included in this review highlight examples of how changes in environmental factors can affect PWD.

Figure 1. Scoping Review Flow Diagram

Results

A total of 42 studies were reviewed in this scoping review. The majority of studies (43%) included in this review used a time series study design. Other common study designs were cohort, case-control, case-crossover, cross-sectional, qualitative, and mixed methods. Of the 42 reviewed studies, 86% reported statistically significant findings or associations in their results, whereas 10% reported no significant findings, and 5% reported qualitative results. A summary of study characteristics including study design and major findings is highlighted in Table 2. The authors read through the methods and results of the selected studies and categorized these based on the nature of the study [extreme temperatures, air pollution, and natural disasters), and outcome type (morbidity, mortality, hospitalization). Major findings from this review suggest climate change impacts PWD through three major mechanisms, namely, extreme temperature, air pollution, and impact from natural disasters (Fig. 2).

Figure 2. Impact of Climate Change on PWD

Extreme temperature

Twenty-five of the reviewed studies examined the effects of extreme temperatures on PWD. Compared to the general population, PWD are more sensitive to extreme temperatures, especially heat, because of impaired thermoregulatory control, regardless of their diabetes type [31].

Diabetes morbidity increases disproportionately at high temperatures [32]. Bunker et al. [13] found that diabetes morbidity increased with heat. Additionally, extreme heat is an independent risk factor for diabetes mortality [33]. Geirinhas et al. [34] found that accumulated heat stress conditions during consecutive days preferentially preceded by persistent periods of moderate temperature, lead to higher excess mortality rather than sporadic single hot days for PWD. Li et al. [35] cite a 14.7–29.2% increase in diabetes mortality with every 1 degree Celsius increase in the daily maximum temperature over the threshold (29°C, 35°C, 33°C and 34°C for Harbin, Nanjing, Shenzhen and Chongqing, respectively). Ma et al. [33] found that short-term exposures to heat were associated with an excess burden of mortality for diabetes patients, with 4.61% of diabetes mortality attributable to heat, results from Isaksen et al. [36] demonstrate that the relative risk of death from diabetes on 99th percentile heat days was 78% greater than on a non-heat day in 45–64-year-olds. Intense and prolonged cold also adversely affect PWD [37]. Li et al. [35] found that both extremely cold and hot temperatures increase diabetes mortality in different manners. Exposure to cold spells was associated with an increased risk of hospital admission [relative risk (RR) = 1.45, 95% confidence interval (CI): 1.26, 1.66] and mortality (RR = 2.02, 95% CI: 1.37, 2.99) due to diabetes [37]. Xu et al. [31] estimated that 7.3% of all hospitalizations due to diabetes in the hot season were attributed to heat exposure in Brazil, and Bai et al. [15] demonstrated that cold and hot temperatures were associated with a 12% (95% CI: 1%, 24%) and a 30% (95% CI: 6%, 58%) increase in hospitalizations from diabetes, respectively. Another study found that short-term heat exposure may increase the burden of diabetes-related hospitalization, especially among the very elderly [31].

Air pollution

Four studies examined the effects of air pollution on PWD. Climate change can induce changes in air quality and has the potential to increase levels of pollutants such as ground-level ozone [38]. Air pollution impairs physiological function [39] including elevated blood glucose for adults with diabetes [40].

Exposures to smoke emitted from wildfires were found to be consistent with other findings associating fine particulate matter (i.e., particulate matter that are 2.5 microns or less in diameter — PM2.5) with increased risk of hospitalization due to diabetes [41], and Stieb et al. [39] found that individuals considered that exhibited at least one risk factor (living with diabetes) were more susceptible to adverse effects of O3 and PM2.5 exposure.

Natural disasters

Thirteen studies explored how PWD may be affected by natural disasters such as hurricanes and earthquakes. These disasters often lead to disruptions in access to medical supplies or care [18] and have the potential to damage healthcare infrastructure [13]. Additionally, in extreme circumstances natural disasters may lead to the displacement of communities [16, 42].

All of these factors may lead to increased difficulty in accessing and storing insulin, reduced access to healthy diets, and reduced glucose monitoring due to lack of supplies. Chowdhury et al. [43] found that at six and nine months after hurricanes Irma and Maria, there was a significant increase in patients being seen for diabetes-related complaints, and Lee et al. [44] reported that patients who had diabetes were more likely to visit emergency departments after Hurricane Sandy, supporting the idea that natural disasters may disproportionally affect PWD and cause medical disruptions.

Continuity of care for chronic diseases, such as diabetes, has been identified as a major concern after a natural disaster [45]. One study found that compared to individuals without diagnosed diabetes, PWD were more likely to report that their household had a 3-day supply of water, a 3-day supply of prescription medication, and an evacuation plan (27.0% vs. 20.6%) [46]. However, Arrieta et al. [45] documented inadequacies of pre-disaster preparation among individuals living with diabetes, classified as a medical management priority, and suggested pre-disaster stockpiling coupled with safe storage, and the staging of supplies in locations just outside the perimeter of a potential disaster area under imminent threat.

Leppold et al. [47] found that patients with diabetes who were affected by Japan’s triple disaster (earthquake, tsunami, and nuclear accidents) experienced a deterioration in their glycemic control following the disasters, demonstrating an increase in the cohort’s mean hemoglobin A1c (HbA1c) rising from 6.77% in 2010 to 6.90% in 2012. They also found that rural residency was associated with a lower likelihood of deteriorating control (OR 0.34, 95% CI 0.13 to 0.84), compared with urban residency.

Travia et al. [48] found the period prevalence of DKA was higher in the six months following Hurricane Matthew compared to before the hurricane. Rates of uncontrolled diabetes were 3.6% higher among veterans who experienced a 6-month closure in their medical center after Superstorm Sandy; however, these impacts were not significant 6 months after the center reopening [49].

Multiple studies found that mortality increased for PWD after exposure to natural disasters. Quast et al. [50] found that seniors with diabetes experienced a 40% increase in all-cause mortality in the first month after Hurricanes Katrina and Rita, Cruz-Cano and Mead [51] reported excess deaths among PWD following Hurricane Maria in Puerto Rico, and Shih et al. [52] found that after Typhoon Morakot a mortality hazard analysis showed that among affected adults with previous cerebrovascular diseases and acute ischemic heart diseases, patients with diabetes had significantly increased mortality rates [adjusted hazard ratio (HR): 1.3–1.7].

Discussion

Clinical and policy implications

As described above, climate change has several clinical implications for PWD. Several studies quantified the effects of climate change on health outcomes of individuals living with diabetes in terms of quality of life, morbidity, and mortality. Multiple studies demonstrated a relationship between exposure to heat events and increased morbidity and mortality for PWD [13, 33, 35, 36, 50–53]. More specifically, studies found increased rates of hospitalizations after exposure to a climate change-induced event [10, 15, 31, 37, 41]. Additionally, many of the environmental hazards induced by climate change have both direct and indirect effects on an individual’s blood glucose levels, leading to poor glycemic control or episodes of DKA [17, 22–24, 40, 47, 49].

One of the first manuals focusing on emergency diabetes care was created by the Japan Diabetes Society following the catastrophic 2011 earthquake [54], and since then additional resources and guidelines have been created by diabetes care specialists to help coordinate and bundle resources for providers and patients [55, 56]. In the 2022 ISPAD Clinical Practice Consensus Guidelines, disaster preparedness is briefly mentioned [57]; however, recommendations from diabetes organizations for disaster-related preparedness for PWD are still lacking. Diabetes professionals should educate PWD on the impacts of climate change and make adequate care plans including sick day plans to mitigate adverse effects [39, 58, 59]. Diabetes teams should emphasize the importance of limiting exposure to extreme temperatures, staying hydrated, and ensuring adequate insulin management [15, 31, 35]. Recommendations should be appropriate to geographic location, season, and with consideration of expected natural disasters, wherever possible [57].

Outside of healthcare, a more coordinated approach from stakeholders including public health, urban planning, community-based partnerships, and disaster preparedness may be beneficial to reduce the impact of climate change on PWD [60]. Disaster preparedness plans should incorporate diabetes considerations (through insulin access, effects of extreme temperatures, etc.) so that preparedness teams are trained to effectively support high-risk individuals like PWD and outline immediate response and long-term support for PWD [61].

Future direction

This scoping review highlights the impacts of environmental hazards on PWD; these hazards such as extreme temperatures, air pollution, and natural disasters are becoming more common in several parts of the world due to climate change. Several systematic reviews have highlighted the effects from climate change induced events on PWD such as exposure to extreme temperatures and risk of hospitalizations [13, 24, 53, 61, 62].

Many of the studies in this review discuss the more immediate impacts of natural disasters on PWD, within six months to a year but do not explore the long- term effects. One study suggested that the effects of natural disasters were mitigated with access to insulin and demonstrated that glycemic deterioration long- term post-disaster can be in part due to a shortage of antidiabetic agents, largely destroyed homes, and changes in working environments [63]. Other systematic reviews have reported on the burden of chronic care management and increased hospitalizations and ED visits after natural disasters [64–66], highlighting the need for continuing management of diabetes care in these areas long term.

Additional studies examining the effects of children with diabetes who are exposed to environmental hazards induced by climate change are needed. For example, Cai et al. [40] demonstrated that medium-term exposure to ambient PM2.5 and PM10 were associated with higher FBG levels in children; however, this population of children was considered to be generally healthy and not living with diabetes.

Only a small number of studies assessed the quality of life or mental health impact of natural disasters for PWD. The independent mental health impact of diabetes [67] and natural disasters [68] are well documented, but the intersection of the two did not appear significantly in the published literature. Understanding this intersection is important to support the lived experience of PWD, further studies are needed in this area [63, 69].

Similarly, structural racism and the impact of social determinants of health predisposes racial and ethnic minorities living with diabetes to a heightened burden of climate change [70, 71]. Communities facing additional burdens of systemic racism, geographical isolation, or socioeconomic disadvantage, such as communities of color, indigenous people, the geographically isolated, and those who are socioeconomically disadvantaged may already be experiencing poor environmental quality and are less likely to adapt to climate change [72]. Supporting literature reported that a major disaster exacerbated existing disparities related to socioeconomic status, in addition to the significant effect it had on diabetes management [18].

Strengths and limitations

Strengths of this scoping review include the long study period (more than 50 years), three primary reviewers, and the review of multiple study designs. Additionally, a second review was carried out by reviewers to include additional search criteria at a later date. This search was conducted to attempt to capture all available research published in this field. This scoping review uniquely assesses climate change induced environmental hazards as well as natural disasters under one umbrella. However, this study has a few limitations. First, the quality of evidence could not be appraised because of the heterogeneity of the study types. Second, only publications in English were considered; it is possible that good-quality studies on the topic may have been published in other languages. Third, although PubMed is generally considered the most comprehensive database for medical literature, it is possible that there could be additional publications in more specialized databases. This risk is mitigated by the inclusion of articles from Google Scholar, which tends to generate much more results from searches than traditional databases. Google Scholar also does a great job of capturing grey literature.

Conclusions

Climate change increases the frequency and intensity of environmental hazards such as extreme temperatures, air pollution, and natural disasters, which increase morbidity and mortality for people with diabetes. Policies that address the interconnection between climate change and diabetes outcomes would improve global diabetes population health. Future research should explore potential solutions to addressing this crisis across multiple populations and settings.

Ethical permission

Ethical approval was not needed for this article.

Funding

None.

Conflict of interests

Dr. Ebekozien has been a member of the Medtronic Diabetes Health Equity Advisory Board. His organization T1D Exchange has received research support on his behalf from Dexcom, Medtronic Diabetes, Eli Lilly, Abbott, Vertex. He has received honoraria from Vertex and Medtronic Diabetes. Dr. Shah reports receiving research grants through the University of Colorado from NovoNordisk, Insulet, Tandem Diabetes Care, Alexion, and Dexcom and honoraria from Dexcom, Insulet, LifeScan, DKSH Singapore, Embecta, and Medscape LLC for consulting and speaking outside the submitted work. All other authors report no conflicts.