A national level study of more than 5.4 million older adults reveals that heat waves significantly increase emergency room (ER) visits and hospitalizations among seniors who are dually eligible for Medicare and Medicaid.

Published in JAMA Health Forumthe study looked at data from 2016 to 2019 in all 50 states and Washington, DC. Heat waves were defined as three or more consecutive days with temperatures above 90°F and in the 97th percentile for daily maximum temperatures. During these times, emergency room visits increased by 10 percent and hospitalizations increased by 7 percent among dual eligibles age 65 and older.

The study also found a worrying 4% increase in death rates during heat waves compared to days without a heat wave. However, nursing home residents showed no significant increase in heat-related emergency visits, which the study authors note is likely due to federal regulations requiring facilities to maintain temperatures between 71°F and 81°F.

Geographical location played a crucial role in the impact of heat. Only three regions—the Northwest, the Ohio Valley and the West—showed statistically significant increases in emergency room visits. In particular, areas such as coastal California, where residents are used to milder temperatures and often lack air conditioning, have shown increased vulnerability.

“Without coping strategies to address the health impact of heat, dually eligible individuals are increasingly likely to experience negative outcomes,” the researchers concluded.

The findings are particularly relevant to the roughly 8 million Americans who qualify for both Medicare and Medicaid (also known as dual eligibles), a group with significant vulnerabilities: 90 percent have annual incomes below $20,000, half report normal or poor health and 40% live alone. The study highlights the need for targeted adaptation efforts to protect this high-risk population during extreme heat events.