Extreme outdoor temperatures—increasingly common due to climate change—are known to worsen chronic diseases such as cardiovascular, respiratory and brain diseases. Now, a study of nearly 3 million geographically diverse patients adds type 2 diabetes to the list of affected diseases.

The thermoregulatory response is often disrupted in older adults with diabetes, making them vulnerable to extreme heat or cold.

Not many studies have been done on the relationship between extreme temperatures and Diabetes Mellitus. Mainly the effect of high temperatures has been studied, such as e.g. what happens in the summer months, to diabetics.

“Both hot and cold weather make it difficult to maintain a relatively stable blood glucose value and increase cardiovascular complications,” says Mr. Antonios P. Lepouras Specialist Pathologist – Diabetologist, Director of Pathology – Diabetes Clinic and Diabetes Center Metropolitan General And it continues:

“Excessive heat, by adversely affecting blood vessels and the nervous system, puts people at risk for reduced intracardiac blood supply and arrhythmia. It is commonly accepted that diabetes impairs the body’s thermoregulatory ability to dissipate excess heat through sweating, leading to overheating. This is probably also due to the dehydration caused, but it could also be related to dilated blood vessels in the skin, which reduce blood flow to the heart.

The cold in turn is itself a stressor for the heart, forcing an increase in blood supply to increase combustion to achieve thermoregulation, constituting a severe test of fatigue and increasing the risks of complications for the “diabetic” heart. Another problem for people with insulin-dependent type 2 diabetes is that the increased blood flow resulting from dry heat exchange with the environment causes insulin to be distributed more rapidly throughout the body, which increases the risk of hypoglycemia. In addition, heat often reduces appetite, which can also lead to low blood sugar. On the contrary, excessive cold, reducing blood circulation, can lead to hyperglycemia followed by dysregulation of diabetes,” he adds.

What about high temperatures?

People with diabetes react more slowly and weaker to heat than those with a healthy metabolism. “This is because their normal ability to adapt to heat can be reduced and function in a limited way. The reason for this is the reduced activity of the sympathetic pathways responsible for the regulation of sweat glands and blood vessels, resulting in delayed absorption of insulin leading to paradoxically elevated blood glucose values.

The main cause is the impairment of heat exchange through sweating and dry heat exchange through the skin, which dissipates heat through dilation of blood vessels in the periphery.

Peripheral nerve damage (peripheral neuropathy) and severe obesity further reduce the ability to adapt to heat and cold. Obesity negatively affects the body’s ability to dissipate heat because the body’s surface area has become smaller relative to body weight. Also, heat diffusion through adipose tissue is slower than through muscle tissue. At the same time in the heat as opposed to the cold, the blood supply to the periphery increases, accelerating the speed of insulin absorption, thus further increasing the risk of hypoglycemia.

Additionally, heat stress can reduce blood flow to the liver and thereby slow the liver’s ability to convert certain drugs from their active to their inactive form. The effect of a strong hypoglycemic drug on the body, such as insulin, could lead to stronger than predicted effects on glucose values ​​(hypoglycemia),” the expert emphasizes.

What about the cold?

“Cold weather can be just as bad as heat for some diabetes outcomes. Epidemiological studies in people with type 2 diabetes have shown poorer glucose control (ie, higher glucose levels) during the winter months. In addition to the effect of cold on the metabolic and thermoregulatory ability of the body of people with diabetes, some other causes may be changes in physical activity during winter, dietary habits, fluid consumption, ability to seek medical care and psychosocial stressors.

The cold, by causing vasoconstriction in the peripheral vessels, reduces the absorption and therefore the activity of insulin, leading to an unexplained increase in glucose with dysregulation of diabetes, increasing the risk of complications” points out Mr. Lepouras.

Extreme weather temperatures and studies on people with diabetes

A pilot study conducted by Penn and colleagues at Penn’s Perelman School of Medicine suggests that very high or low outside temperatures increase the occurrence of three potentially life-threatening conditions for people with type 2 diabetes, including: severe hypoglycaemia (low blood sugar), diabetic ketoacidosis (too acidic blood) and sudden cardiac arrest/ventricular arrhythmia (sudden loss of heart function/very fast heart rate).

Their study, “Climate change and extreme ambient temperature: Association with severe hypoglycemia, diabetic ketoacidosis, and sudden cardiac arrest/ventricular arrhythmia in people with type 2 diabetes,” appears in Diabetes Care January 2024.

The conclusion of the study is that type 2 diabetes is more difficult to regulate in extreme temperatures. The team found that over the course of about two years, study subjects experienced higher rates of hypoglycemia and sudden cardiac arrest in both high (above 100 F/37.7 C) and cold (below 10 F/12.2 C) temperatures than that during milder weather. With diabetic ketoacidosis, the incidence increased when temperatures fell, but not when they rose.

In another study conducted by Aayush Visaria, Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, New Jersey, and colleagues and published online December 7, 2023 in Diabetes Care, researchers evaluated the association between ambient heat and the risk of hypoglycemia in approximately 2 million and approximately 283,000 patients aged 65–100 years with diabetes from the United States and Taiwan, respectively, receiving insulin:

• A serious hypoglycemic event was defined as an emergency department visit or an unplanned hospital admission for hypoglycemia between June 1 and September 30, 2023
• Medication use was defined as at least one prescription (Medicare system) insulin administration within 90 days of the index event
• Median heat index (HI), a combination of ambient temperature and humidity exposure, was calculated by zip code and grouped into percentiles: ≥ 99th, 95–98th, 85–94th, 76–84th, 25–74th, and < 25th
• Among insulin users overall, 32,461 and 10,162 older adults from the United States and Taiwan, respectively, experienced a hypoglycemic episode
• The risk of a severe hypoglycemic episode was about 40% higher among insulin users the higher the ambient temperature and humidity, (≥ 99°)
• In contrast, on days with low HI (< 25th percentile), the risk of hypoglycemia among insulin users was reduced
• No substantial differences in risk for hypoglycemic events and HI were observed by climate region in any of the countries, such as between the US Northeast and Southwest.

In practice: People with inadequately treated type 2 diabetes in high temperature extremes can have dysregulated blood sugar levels, which together with environmental stress increases the risk of acute complications. Also, accompanying secondary diseases, such as high blood pressure and cardiovascular diseases, can be aggravated in high or low temperatures. The risk of heart attack caused by heat as well as cold in people with Diabetes Mellitus is increased due to poor blood supply to the heart.

Good to know that: The following factors increase the risk of reduced tolerance to extreme temperatures in people with diabetes:

• Old
• Long-term Diabetes Mellitus, especially if it is not well regulated
• Obesity
• Insulin therapy
• Comorbidities and accompanying secondary diseases

General – useful instructions for people with Diabetes Mellitus

• Drink enough fluids: Drinking enough fluids is the most important thing. Equally important is the consumption of vegetables and fruits, unprocessed whole-grain carbohydrates and low-fat proteins, for energy and to cover electrolyte disturbances. This advice is especially true for older people with diabetes. A minimum of 1.5-2.5 liters per day is recommended, ideally in the form of water or other calorie-free beverages such as unsweetened tea. Drinks with added sugar and alcohol should be avoided. In case of symptoms, such as dizziness or fatigue, especially the elderly should seek medical help immediately
• Store insulin properly: Those who need insulin should make sure they have enough and that it is stored properly at 2 to 10 degrees. The pen currently in use should not be stored at temperatures below 2 or above 30 degrees, i.e. not on a windowsill or in direct sunlight. Insulin is very sensitive to high temperatures and becomes inactive when exposed to temperatures above 30 degrees. Note that insulin also cannot be frozen as it will become inactive
• Keep meters and test strips away from extreme temperatures: Extreme temperatures can also adversely affect blood sugar meters and strips. Measuring devices, test strips, insulin pumps and other diabetes treatment aids should be stored at normal room temperature. They should also not be refrigerated, as the low temperature can lead to false readings
• Adjust doses of insulin and medications: In hot or very cold weather, those treated with insulin or tablets should talk to their doctor to discuss the dosage of blood sugar-lowering tablets and their possible adjustment. Other medicines, such as medicines to lower blood pressure, should also be checked
• Regularly check blood sugar levels: In general, on days with extreme temperatures, those with type 2 diabetes, especially if treated with insulin, should check their blood sugar levels at least two to three times a day
Apart from these special instructions, on extremely hot or very cold days, they can and should follow the same general advice given to people with a healthy metabolism.

Even in winter or summer, adequate exercise and physical activity remains essential. On particularly hot or very cold days, physical activity should be done early in the morning or in the afternoon in a closed, air-conditioned space to avoid stressing the cardiovascular system.

“With proper education and regular communication with their treatment team, people with type 2 diabetes can avoid or successfully manage the adverse effects of diabetes management in extreme weather temperatures that are unfortunately now commonplace along with the possibly coming climate change” concludes Mr. Lepouras.