Medications for chronic diseases affect the body’s ability to regulate body temperature, keep cool

The group, led by Associate Professor Jason Lee from the Human Potential Translational Research Programme at the Yong Loo Lin School of Medicine, National University of Singapore (NUS Medicine), identified and reviewed relevant research papers using keyword searches on databases such as PubMed and Google Scholar. These papers studied the associations and effects of medications on thermoregulation. The review findings were presented in a topical manner, focusing on medication classes used to treat commonly diagnosed chronic conditions (e.g., diabetes, cardiovascular disease, neurodegenerative disease, and cancer). The findings were published in Pharmacological Reviews, titled Effects of Medications on Heat Loss Capacity in Chronic Disease Patients:

Health Implications Amidst Global Warming

The findings show that medications used to treat common chronic conditions, like blood thinners, blood pressure drugs, Parkinson’s disease/Alzheimer’s medications, and some chemotherapy drugs, can make it harder for the human body to handle hot weather by reducing its ability to sweat or increase blood flow to the skin.

Lead author and second-year PhD candidate from the Human Potential Translational Research Programme Mr Jericho Wee said, “Rising global temperatures caused by climate change pose a significant health concern for clinical patients reliant on long-term medications and healthcare. Increasingly, we will continue to see more elderly patients, many who have multiple health conditions and are taking different types of medication concurrently to manage their chronic diseases, compounding the risk of heat-related illness and dehydration. Understanding how each medication impacts thermoregulation, in the face of warmer environments, is the crucial first step to predicting the possible health outcomes when multiple medications are taken concurrently.” While previous reviews have highlighted the impacts of medications on heat, the scope of those reviews did not present the evidence in the context of the chronic diseases and ageing. The team’s narrative review presents the evidence in the context of high ambient temperatures and their impact on chronic disease sufferers who are on long-term and life-long medication.

Senior author Assoc Prof Jason Lee said, “This review emphasises the importance of studying the mechanisms of altered thermoregulation in individuals with diabetes and other cardiometabolic conditions to prevent heat-induced conditions. This is most relevant in Singapore and many other countries, where we have rapidly ageing populations and rising ambient temperatures. Pharmacological and thermal physiologists should focus transdisciplinary efforts on this area of research to refine and enhance safe medication prescription guidelines to preserve the health of people who need these medications, even in hot weather.”

Assoc Prof Melvin Leow, the review’s co-author and Senior Consultant Endocrinologist at Tan Tock Seng Hospital said, “Physicians are often unaware of the potential harms certain drugs may cause by compromising the body’s thermoregulatory control mechanisms. This is an especially important area to delve into as those with chronic diseases and older adults are susceptible to adverse health outcomes in the heat, due to their reduced thermoregulatory capacity. It is timely and prudent that scientists and doctors collaborate even closer in this important field that cuts across a wide range of medical disciplines.”

The study was supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) Programme.

The findings, in brief:

Cancer

Patients on certain cancer medications have reported symptoms of hot flushes, such as inappropriate sweat responses and an increase in core temperature which affects quality of life. Exercise and improved fitness levels have been shown to reduce the frequency of hot flushes and improve thermoregulatory responses in other chronic conditions such as diabetes, and it remains a crucial component in maintaining the nervous and cardiovascular functions of cancer patients. However, bodily impairments and limitations caused by chemotherapy and medications may limit their ability to exercise, which perpetuates a cycle of loss in exercise capacity that is crucial to their recovery.

Cardiovascular disease

Patients who have cardiovascular diseases, such as coronary heart disease, stroke and heart failure, are more vulnerable to high heat exposure because their hearts will be working harder to deliver blood to the skin and working muscles to maintain core temperature at an optimal level whilst maintaining work output. Anti-platelet medications, such as aspirin and clopidogrel, are usually taken to prevent blood clots from forming in the blood vessels, that could lead to stroke or heart disease. Yet, these anti-platelet medications may increase core temperature, whether at rest or during exercise. These medications also reduce skin blood flow and suppress sweat responses, which means thermoregulatory responses would be less sensitive to accumulated heat, and delay in cooling itself down, which could lead to heat stroke.

Used for multiple cardiovascular conditions, such as ischemic heart disease, high blood pressure, and heart failure, beta-blockers can reduce skin blood flow during heat stress by reducing blood pressure and facilitating additional constriction of skin blood vessels. However, the findings of the effects of beta-blockers on sweat responses remain mixed, with some studies showing no changes in sweating, while others demonstrate reduced sweating. As such, greater research efforts are needed to understand how different types of beta-blockers may impact sweating.