Climate change and diabetes 

As the planet warms, people with diabetes are beginning to experience health impacts from climate-related factors such as heat, air pollution, extreme weather events and infectious diseases. A new review in Diabetologia looks at climate change and diabetes, and how stakeholders can work together to help people with diabetes deal with this emerging threat to their health. Dr Susan Aldridge reports. 

Climate change is a threat to human health, as well as that of the planet. There were over 345,000 heat-related deaths worldwide in people over 65 in 2019 – an 80% increase on the average number of deaths over the years 2000 to 2005. Infants, older people and people with chronic conditions, including diabetes, are more vulnerable to extreme heat. People with diabetes have impaired responses to heat stress and comorbidities, such as cardiovascular disease and chronic kidney disease, also make them more susceptible to high temperatures. This is particularly concerning, given that not only is the prevalence of diabetes around the world on the increase, but the number of days that people are exposed to extreme heat has also increased over recent decades. 

As well as heat, air pollution, extreme weather events and infectious diseases are all likely to become more common with climate change. Jacqueline Ratter-Rieck, Michael Roden and Christian Herder of the German Diabetes Center in Düsseldorf, Germany, have reviewed studies on the impact of these environmental factors on people with diabetes and make some suggestions on how to manage this emerging health challenge. 

Heat

So far, only a few studies have looked at the relationship between ambient temperature and diabetes. A study of the impact of changes in outdoor temperature on diabetes incidence in the USA between 1996 and 2009 suggested that a 1°C rise in outdoor temperature is linked to over 100,000 new cases of diabetes each year. The same authors found an association between mean annual temperature and age-, sex-, income- and obesity-adjusted prevalence of increased fasting blood glucose by country. 

A similar relationship between ambient temperature and dysglycaemia and insulin resistance was also noted in a cohort of Spanish adults. Dehydration may drive the physiological mechanism underlying the link between higher temperatures and insulin resistance, but further investigation is needed.

Several studies have also shown that higher temperatures, particularly during heatwaves, are associated with increased need for medical advice and hospitalisations among people with diabetes. It should be noted that cold spells also increase this risk. A study analysing daily deaths from diabetes in four cities in the Philippines detected elevated mortality risk at both low and high ambient temperatures. Thus, extremes of temperature are risky for people with diabetes, whether this is due to the temperature itself or to resulting changes in lifestyle, or a combination of both.

Air pollution

Climate change-induced changes in temperature and rainfall can increase air pollution through increasing levels of particulate matter and ozone. Many studies have shown that air pollution is associated with insulin resistance and the risk of developing diabetes. Indeed, it has been estimated that around 20% of the global burden of type 2 diabetes may be attributed to fine particulate matter (PM_2.5) pollution.

Air pollution has also been shown to contribute to diabetic complications, such as cardiovascular mortality, heart failure and neuropathy. This means that long-term exposure to air pollution will contribute to the rise in diabetes incidence and the burden of complications.

Short-term exposure to air pollution is also relevant in diabetes. Increasing ambient temperatures and drought have caused exposure to wildfires to increase in 134 out of 185 countries between 2017 and 2020, compared with the period 2001 to 2004. Wildfire smoke is a potent mix of PM_2.5, carbon monoxide and ozone pollution. Wildfires can expose large regions to their smoke, as seen earlier this year, when smoke from Canadian wildfires was clearly visible in the streets of cities in the United States. This means many people with diabetes will be exposed to it. One study has shown an increased number of respiratory and cardiovascular-related physician visits among people with diabetes after wildfires, as well as increased cardiovascular morbidity, particularly among those over 65. 

Meanwhile, short-term exposure to PM_2.5 is known to impair glycaemic control. Research is needed to determine whether this is also the case for exposure to wildfire smoke. Finally, it will also be important to determine whether the impact of wildfire smoke on blood glucose levels or hospitalisation of people with diabetes arises directly from exposure to pollution and how other factors such as psychological stress or accessibility of healthcare services also contribute.  

Extreme weather events

The frequency and intensity of weather extremes have increased in recent years, largely because of climate change. Heatwaves, droughts, flooding and storms all pose a severe risk to public health. For people with diabetes, there are many challenges – restricted access to care, psychological stress and lifestyle changes – that may affect glycaemic control. Indeed, several studies show that exposure to natural disasters can worsen glycaemic control. For instance, a study of people with diabetes affected by Hurricane Katrina in 2005 showed worsened glycaemic control up to 16 months later. Moreover, the rise in HbA1c was dependent on whether participants were using public or private healthcare, suggesting that exposure to natural disasters may increase health inequalities and highlighting a need for targeted interventions following such events. 

The above study also revealed deterioration in blood pressure and lipids, which can increase the risk of hospitalisation for people with diabetes. Such an increase was noted in a study of Hurricane Sandy, where more people with diabetes aged over 65 visited the emergency room than other vulnerable populations, presenting with hypertension, myocardial infarction or kidney disease. And a long-term follow-up also showed that older people impacted by Hurricanes Katrina and Rita had higher all-cause mortality risk directly after the event, and also up to 10 years later.

Finally, depression is a common comorbidity of diabetes. Research is sparse, but people with diabetes may experience increased psychological burden after extreme weather events involving death and destruction. They may therefore require additional emotional and psychological support. 

Infections

Over 58% of viral, bacterial and fungal infections could be aggravated by climate change, according to a recent estimate. For instance, rising temperatures have already led to the expansion of the Asian tiger mosquito, which transmits zika, dengue and chikungunya virus, into Europe. People with diabetes are known to be more at risk of severe infections because of altered immune cell profiles and responses. In individuals infected with chikungunya virus, diabetes is the second most prevalent comorbidity after hypertension. Diabetes is also a risk factor for West Nile or dengue virus infection and may lead to longer, more severe disease.  

The molecular mechanisms underlying these vulnerabilities remain elusive. Therefore, research into immune responses in infected people with diabetes compared with those in people without diabetes would be of great value and may help identify those at increased risk of severe infection. 

Management and mitigation

Heat, air pollution, extreme weather events and infections represent significant climate-related health threats for people with diabetes. To mitigate their impact on morbidity and mortality, and limit associated healthcare costs, a concerted effort is needed by people with diabetes, healthcare professionals and policy makers. 

People with diabetes should apply their own personal strategies to minimise the impact of heat and air pollution on health. There is structured information available on multiple platforms, including those of Diabetes UK and the Centers for Disease Control and Prevention. Healthcare professionals can also provide relevant support. In particular, they can adjust or advise on medication, such as reducing diuretic doses during heatwaves or advising on the stability and absorption of insulin in the heat. Meanwhile, planetary health education should be included in curricula for medical students and this information included in diabetes care.  

At the national and international level, although 190 countries signed the Paris agreement to take action to limit global warming, efforts need to increase rapidly if targets are to be met in time. Specific mitigation strategies need to be developed to reduce the impact of heat and air pollution on health. Heat-health action plans (HHAPs) could be central to such national prevention and control approaches. According to a recent study, 17 out of 27 countries in Europe already have a HHAP and have even begun to implement some of the core HHAP elements. Considering the needs of people with diabetes, it is encouraging that the core element ‘particular care for vulnerable groups’ is one of these being worked on and that the majority of HHAPs mention people with chronic conditions. However, the core elements ‘preparedness of health and social systems’ and ‘long-term urban planning’ still need a lot of work. 

Towards climate resilience

Going forward, the authors say sustainable research, prevention and control strategies are needed to foster resilience to the health impacts of climate change among people with diabetes. There are many unanswered questions. For instance, what is the impact of increased temperatures on hypoglycaemia and do glucose-lowering drugs affect people’s thermoregulation? More research will help to identify predisposing factors to climate-based health impacts so that people can be advised accordingly. Heat warnings and action plans by public health authorities would also help prevent adverse health effects.

Not everyone with diabetes will be equally vulnerable to climate-related health impacts. We already know that older people and those with comorbidities will be most at risk. And, in the light of recent approaches to diabetes reclassification, the authors speculate that some phenotypes may also be more at risk than others. For instance, severe insulin-resistant diabetes (SIRD) may pose added vulnerability to heat because of frequent comorbidities, such as hypertension, and also to infection because of altered immunity. Further research on diabetes heterogeneity may help identify specific climate-associated risks for different patient groups.

Finally, in addition to mitigation strategies for those who already have diabetes, the prospect of adverse health effects from climate change adds urgency to the need to prevent diabetes. Moreover, prevention strategies, such as a healthy, sustainable diet, not only improve human health but also reduce the environmental footprint, thereby benefiting planetary health.  

To read this paper, go to: Ratter-Rieck JM, Roden M, Herder C. Diabetes and climate change: current evidence and implications for people with diabetes, clinicians and policy stakeholders. Diabetologia 25 March 2023. https://doi.org/10.1007/s00125-023-05901-y

To learn more about helping patients to manage their diabetes, enrol on the EASD e-Learning course ‘Patient education and support’.

Any opinions expressed in this article are the responsibility of the EASD e-Learning Programme Director, Dr Eleanor D Kennedy.