Worsening heat waves pose unique risks to people living with neurodegenerative disease

As 2024 is set to end as Earth’s hottest year on record—breaking the previous record set in 2023– a UCLA Health researcher says people living with neurodegenerative diseases will be uniquely vulnerable to worsening heat waves because of a higher risk of heat-related complications.

In a commentary published in JAMA Neurology, Dr. Indu Subramanian said that doctors have a duty to strengthen the understanding of heat-related impacts on people living with diseases such as dementia or Parkinson’s disease and to develop updated solutions to protect these vulnerable patients in a warming world.

“This editorial makes clear that these deaths are preventable, and doctors can make a difference,” Subramanian said.

While more frequent and severe heat waves pose health risks to all people experiencing them, their impacts can be exacerbated among people with neurodegenerative disease due to symptoms or treatments associated with them, Subramanian said.

Heat has been shown to worsen neurodegenerative disease symptoms. In Parkinson’s disease, symptoms such as a malfunctioning autonomic nervous system can increase the risk of dehydration, heat stroke and fainting caused by reduced blood flow to the brain. Symptoms of Parkinson’s disease and other conditions can also compromise sweating, which would only worsen especially in areas with high humidity. Subramanian said worsening symptoms can impair a person’s ability to perform regular activities such as taking medication, turning on air conditioners, rehydrating or taking a cold shower to keep cool.

Some medications that treat these diseases, such as anticholinergics and tricyclics, can inhibit functions such as sweating and blood flow to the skin that help to passively cool the body.

One study in 2020 led by the University of Malta found statistically significant increases of more than 10% for both Parkinson’s disease-related mortality and hospital admissions at temperatures of only 1 degree Fahrenheit over a threshold of 93 degrees Fahrenheit. A separate study in 2019 from the Queensland University of Technology, cited by Subramanian, found similar trends for Alzheimer’s disease patients.

The Queensland University of Technology study also found an association between heat-related mortality and the amount of green space near a person’s residence. Green space works to prevent heat islands by providing shade, deflecting radiation and releasing moisture. The study found people living near low amounts of green space had three times the risk of heat-related mortality.

As the U.S. population of older residents increases, so has the number of people living with neurodegenerative diseases such as dementia. Thermoregularity, the ability to maintain body temperature, is often compromised among older people. Heat-related complications are also higher for men, though the reason for this increased risk is still unclear, Subramanian said. The increasing social isolation among older adults can also increase risk of heat-related issues because of lack of early detection.

“I was surprised how many patients view us docs or health care providers as their only touch point with the world outside their house,” Subramanian said.

To address these many issues, Subramanian states that medical providers and institutions must establish best-practice guidelines and tie these quality measures to reimbursement and certification. One example would be to have doctors regularly screen people with neurodegenerative diseases for social isolation and to connect them to resources. The increased utilization of telemedicine can also be used to have medical providers check in on high-risk patients and proactively contact them during high temperature periods, Subramanian said. Doctors can take early steps by providing early handouts to patients with information and resources.

“People with Parkinson’s disease and dementias are at risk of dying in heat waves and we can be proactive about preventing this,” Subramanian said.

The editorial was coauthored by Dr. Ali Saad of the University of Colorado, Aurora, who is one of the only neurologists to have completed a Climate Change Fellowship. Dr. Subramanian is also board-certified in integrative medicine.