Aging and extreme heat combine to raise risk of deadly infections

As we age, extreme heat causes many heat-related illnesses that can lead to serious health issues. A new study from the University of California, Irvine's Joe C. Wen School of Population & Public Health adds to that list.

The UC Irvine researchers have discovered that the combined effects of aging and heat waves are putting people's health at greater risk by weakening gut and immune system function, which heightens our risk of infection from a deadly, waterborne bacterium called Vibrio vulnificus that is increasingly found in warmer ocean waters.

With more frequent and intense heat waves and the population continuing to age, this research, published in the journal Science of the Total Environment, offers insight into how these two factors work together to weaken the immune system, damage the gut, and elevate the risk of severe infection. The work was supported by the National Institute of Environmental Health Sciences.

As many around the world experience record-breaking June heat waves, the study arrives at a crucial moment in the ongoing effort to understand how rising temperatures affect human health.

While Vibrio vulnificus infections are already a growing concern in warming coastal regions, our findings show that extreme heat, especially with older individuals, may further compromise the immune system and gut microbiome in ways that make people more susceptible. It's a double hit: Aging weakens immune defenses, and heat stress accelerates that decline."

Saurabh Chatterjee, corresponding author, professor of environmental & occupational health, and medicine

As V. vulnificus infections and extreme heat events increase, key scientific gaps have made it difficult to assess infection risk. Until now, researchers have lacked a clear understanding of how prolonged heat affects the gut microbiome, immune response and infection vulnerability in older people.

To address this, the UC Irvine team exposed both young and aged mice to climate-relevant heat and conducted microbiome sequencing along with tests for gut integrity and immune function. The aged mice showed significantly more damage to the intestinal barrier, systemic inflammation, immune dysfunction and antibiotic-resistant genes in the gut microbiome than their younger counterparts.

This work is the first to connect climate-driven heat stress with gut and immune disruption that raises susceptibility to V. vulnificus. It also identifies a potential avenue for treatment: Aged mice treated with a beneficial gut microbe (Roseburia intestinalis) demonstrated restored immune cell function and reduced signs of infection. Reintroducing key probiotics helped improve intestinal health and regulate the immune system. The results suggest that supporting gut health may be key to boosting immune resilience during heat exposure.

Additional contributors were UC Irvine doctoral students Subhajit Roy (lead author), Punnag Saha, Madhura More, Ayushi Trivedi and Dipro Bose – all members of Wen Public Health's Environmental Health and Disease Laboratory; and Susmita Das, Zahid Hayat Mahmud and S.M. Manzoor Ahmed Hanifi of Bangladesh's International Centre for Diarrhoeal Disease Research.