Sean Hennessy
Sean Hennessy, PhD, PharmD

Produced in conjunction with the Population Aging Research Center at the University of Pennsylvania.

Extreme outdoor temperatures—which are becoming more common due to climate change—are known to worsen chronic medical conditions such as cardiovascular, respiratory, and cerebrovascular diseases, such as strokes. Now, a study of almost 3 million geographically diverse Medicaid patients adds type 2 diabetes to the list.

The pilot research, conducted by LDI Senior Fellows Charles Leonard and Sean Hennessy, along with Kacie Bogar of Penn’s Perelman School of Medicine, and other colleagues, suggests that very high or low outdoor temperatures increase the occurrence of three potentially life-threatening conditions for people with type 2 diabetes: serious hypoglycemia (low blood sugar), diabetic ketoacidosis (overly acidic blood), and sudden cardiac arrest/ventricular arrhythmia (abrupt loss of heart function/too-fast heart rate). Their study, “Climate Change and Ambient Temperature Extremes: Association with Serious Hypoglycemia, Diabetic Ketoacidosis, and Sudden Cardiac Arrest/Ventricular Arrhythmia in People with Type 2 Diabetes,” appears in Diabetes Care.

Charles Leonard, PharmD, MSCE

“[Type 2 diabetes] is more challenging to control during extreme temperatures,” said Leonard, an assistant professor of epidemiology. The Penn-led team found that over the course of about two years, study subjects experienced higher rates of hypoglycemia and sudden cardiac arrest during both high (over 100 F) and low temperatures (under 10 F) than they did during more moderate weather. With diabetic ketoacidosis, the incidence rose when temperatures fell, but not when they got warmer.

The study carries implications for health equity considerations. Disadvantaged people such as the Medicaid recipients who were subjects of this research are more likely than other Americans to develop type 2 diabetes, which is predicted to become somewhat more prevalent in the U.S. as global warming increases. Because people in lower socioeconomic brackets more often experience temperature extremes—due to a lack of air conditioning, for instance—those with type 2 diabetes are particularly susceptible to adverse health outcomes. Study subjects came from a diverse group of states, including California, Florida, New York, Ohio, and Pennsylvania.

Why are Extreme Temperatures Dangerous?

Not a lot of work has been done on the relationship between extreme temperatures and diabetes. “But, it is pretty well accepted that because of damage to blood vessels and nerves, diabetes impairs the body’s capacity to dissipate excess heat through sweating. Overheating puts people at risk for arrhythmia. This is probably due to dehydration but could also be related to dilated blood vessels in the skin, reducing blood flow to the heart,” said Leonard.

“Heat stress may decrease liver blood flow and thereby slow the liver’s ability to convert certain drugs from their active to inactive forms,” he added. “Having a more active drug in the body could lead to stronger than intended pharmacological effects,” Leonard explained. In addition, both hot and cold weather make maintaining a steady amount of glucose in the blood difficult.

“Cold weather can be just as bad as heat for some diabetes outcomes,” said Leonard. “This is likely multifaceted. Prior work among persons with type 2 diabetes has shown poorer glucose control (that is, higher glucose levels) during winter months. Some factors in play might be wintertime changes in physical activity, eating habits, fluid consumption, the ability to seek medical care, and psychosocial stressors,” Leonard said.

The research findings suggest that doctors who treat diabetes should ask about their patients’ exposure to high or low temperatures in their homes and neighborhoods. “While a single epidemiologic study like ours should not in-and-of itself drive changes to clinical decision-making, I hope that clinicians become more attuned to the environments experienced by their patients with diabetes,” Leonard said. Such conversations might alter, for example, a patient’s decision to live in or travel to a very hot area.

Can Statin Drugs Moderate the Impact of Heat?

People with diabetes are routinely prescribed cholesterol-lowering statins to reduce their high risk of heart disease. In out-of-the-box research, Hennessy, Leonard, and others found that, in a general Medicaid population, statin use lowered death rates when temperatures soared over 95 F. Statins appear to increase blood flow, and hence heat dispersal, through mechanisms that are independent of their effect on cholesterol. Any drug that reduces the negative impact of heat on people with diabetes (and others) is welcome.

“If these results hold up in other studies, it would be reasonable for doctors to remind their type 2 diabetes patients to take their statins during hot periods. And there might be a group of patients who normally don’t take statins but would benefit from their use when temperatures are high,” said Hennessy, a professor of epidemiology at Penn.

The search for what the team calls “thermo-protective” drugs becomes more and more important as the earth grows warmer. “There’s a large potential for impacting population health,” noted Hennessy. He added that only a very small group of researchers is working in this area.

Leonard and his collaborators are part of this group. “Thanks to funding from Penn’s Population Aging Research Center and the Center for Real-world Effectiveness and Safety of Therapeutics, I’m currently examining how ambient temperature extremes may differently impact persons treated with distinct anti-diabetes drug regimens. Some interesting findings are forthcoming,” Leonard said.

The team is also looking into environmental factors beyond hot and cold temperatures. “We have some preliminary data on the role of ground-level ozone on rates of bad outcomes in persons with type 2 diabetes. We hope to publish these data soon,” Leonard added.

The study, “Climate Change and Ambient Temperature Extremes: Association with Serious Hypoglycemia, Diabetic Ketoacidosis, and Sudden Cardiac Arrest/Ventricular Arrhythmia in People with Type 2 Diabetes,” was published on October 7, 2022 in Diabetes Care. Authors include Kacie Bogar, Colleen Brensinger, Sean Hennessy, James H. Flory, Michelle L. Bell, Christopher Shi, Warren B. Bilker, and Charles E. Leonard.

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